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cecafdb: a curated database for the documentation, visualization and comparative analysis of central carbon metabolic flux distributions explored by 13c-fluxomics.the central carbon metabolic flux database (cecafdb, available at http://www.cecafdb.org) is a manually curated, multipurpose and open-access database for the documentation, visualization and comparative analysis of the quantitative flux results of central carbon metabolism among microbes and animal cells. it encompasses records for more than 500 flux distributions among 36 organisms and includes information regarding the genotype, culture medium, growth conditions and other specific information ...201425392417
crystal structure of the full-length atpase gspe from the vibrio vulnificus type ii secretion system in complex with the cytoplasmic domain of gspl.the type ii secretion system (t2ss) is present in many gram-negative bacteria and is responsible for secreting a large number of folded proteins, including major virulence factors, across the outer membrane. the t2ss consists of 11-15 different proteins most of which are present in multiple copies in the assembled secretion machinery. the atpase gspe, essential for the functioning of the t2ss, contains three domains (n1e, n2e and cte) of which the n1e domain is associated with the cytoplasmic do ...201425092625
xanthomonas campestris rpfb is a fatty acyl-coa ligase required to counteract the thioesterase activity of the rpff diffusible signal factor (dsf) synthase.in xanthomonas campestris pv. campestris (xcc), the proteins encoded by the rpf (regulator of pathogenicity factor) gene cluster produce and sense a fatty acid signal molecule called diffusible signalling factor (dsf, 2(z)-11-methyldodecenoic acid). rpfb was reported to be involved in dsf processing and was predicted to encode an acyl-coa ligase. we report that rpfb activates a wide range of fatty acids to their coa esters in vitro. moreover, rpfb can functionally replace the paradigm bacterial ...201424866092
involvement of proline oxidase (puta) in programmed cell death of xanthomonas.xanthomonas campestris strains have been reported to undergo programmed cell death (pcd) in a protein rich medium. protein hydrolysates used in media such as nutrient broth comprise of casein digest with abundance of proline and glutamate. in the current study, x. campestris pv. campestris (xcc) cells displayed pcd when grown in pcd inducing medium (pim) containing casein tryptic digest. this pcd was also observed in pcd non-inducing carbohydrate rich medium (pnim) fortified with either proline ...201424788936
secondary structure preferences of mn (2+) binding sites in bacterial proteins.3d structures of proteins with coordinated mn(2+) ions from bacteria with low, average, and high genomic gc-content have been analyzed (149 pdb files were used). major mn(2+) binders are aspartic acid (6.82% of asp residues), histidine (14.76% of his residues), and glutamic acid (3.51% of glu residues). we found out that the motif of secondary structure "beta strand-major binder-random coil" is overrepresented around all the three major mn(2+) binders. that motif may be followed by either alpha ...201424778647
functional characterization of osmotically inducible protein c (mg_427) from mycoplasma genitalium.mycoplasma genitalium is the smallest self-replicating bacterium and an important human pathogen responsible for a range of urogenital infections and pathologies. due to its limited genome size, many genes conserved in other bacteria are missing in m. genitalium. genes encoding catalase and superoxide dismutase are absent, and how this pathogen overcomes oxidative stress remains poorly understood. in this study, we characterized mg_427, a homolog of the conserved osmc, which encodes hydroperoxid ...201424363346
disruption of gene pqqa or pqqb reduces plant growth promotion activity and biocontrol of crown gall disease by rahnella aquatilis hx2.rahnella aquatilis strain hx2 has the ability to promote maize growth and suppress sunflower crown gall disease caused by agrobacterium vitis, a. tumefaciens, and a. rhizogenes. pyrroloquinoline quinone (pqq), a cofactor of aldose and alcohol dehydrogenases, is required for the synthesis of an antibacterial substance, gluconic acid, by hx2. mutants of hx2 unable to produce pqq were obtained by in-frame deletion of either the pqqa or pqqb gene. in this study, we report the independent functions o ...201425502691
arabidopsis and maize rida proteins preempt reactive enamine/imine damage to branched-chain amino acid biosynthesis in plastids.rida (for reactive intermediate deaminase a) proteins are ubiquitous, yet their function in eukaryotes is unclear. it is known that deleting salmonella enterica rida causes ser sensitivity and that s. enterica rida and its homologs from other organisms hydrolyze the enamine/imine intermediates that thr dehydratase forms from ser or thr. in s. enterica, the ser-derived enamine/imine inactivates a branched-chain aminotransferase; rida prevents this damage. arabidopsis thaliana and maize (zea mays) ...201425070638
mechanism of escherichia coli resistance to pyrrhocoricin.due to their lack of toxicity to mammalian cells and good serum stability, proline-rich antimicrobial peptides (pr-amps) have been proposed as promising candidates for the treatment of infections caused by antimicrobial-resistant bacterial pathogens. it has been hypothesized that these peptides act on multiple targets within bacterial cells, and therefore the likelihood of the emergence of resistance was considered to be low. here, we show that spontaneous escherichia coli mutants resistant to p ...201424590485
rapid identification of stenotrophomonas maltophilia by peptide nucleic acid fluorescence in situ hybridization.the objective of this study was to develop a novel peptide nucleic acid (pna) probe for stenotrophomonas maltophilia identification by fluorescence in situ hybridization (fish). the probe was evaluated using 33 human and veterinary clinical s. maltophilia isolates and 45 reference strains representing common bacterial species in the respiratory tract. the probe displayed 100% sensitivity and 100% specificity on pure cultures and allowed detection in sputum from cystic fibrosis patients. the dete ...201425356348
proteinaceous determinants of surface colonization in bacteria: bacterial adhesion and biofilm formation from a protein secretion perspective.bacterial colonization of biotic or abiotic surfaces results from two quite distinct physiological processes, namely bacterial adhesion and biofilm formation. broadly speaking, a biofilm is defined as the sessile development of microbial cells. biofilm formation arises following bacterial adhesion but not all single bacterial cells adhering reversibly or irreversibly engage inexorably into a sessile mode of growth. among molecular determinants promoting bacterial colonization, surface proteins a ...201324133488
cis-2-dodecenoic acid quorum sensing system modulates n-acyl homoserine lactone production through rpfr and cyclic di-gmp turnover in burkholderia cenocepacia.burkholderia cenocepacia employs both n-acyl homoserine lactone (ahl) and cis-2-dodecenoic acid (bdsf) quorum sensing (qs) systems in regulation of bacterial virulence. it was shown recently that disruption of bdsf synthase rpffbc caused a reduction of ahl signal production in b. cenocepacia. however, how bdsf system influences ahl system is still not clear.201323815566
two quorum sensing systems control biofilm formation and virulence in members of the burkholderia cepacia complex.the burkholderia cepacia complex (bcc) consists of 17 closely related species that are problematic opportunistic bacterial pathogens for cystic fibrosis patients and immunocompromised individuals. these bacteria are capable of utilizing two different chemical languages: n-acyl homoserine lactones (ahls) and cis-2-unsaturated fatty acids. here we summarize the current knowledge of the underlying molecular architectures of these communication systems, showing how they are interlinked and discussin ...201323799665
mamp (microbe-associated molecular pattern) triggered immunity in plants.plants are sessile organisms that are under constant attack from microbes. they rely on both preformed defenses, and their innate immune system to ward of the microbial pathogens. preformed defences include for example the cell wall and cuticle, which act as physical barriers to microbial colonization. the plant immune system is composed of surveillance systems that perceive several general microbe elicitors, which allow plants to switch from growth and development into a defense mode, rejecting ...201323720666
interspecies interaction between pseudomonas aeruginosa and other microorganisms.microbes interact with each other in multicellular communities and this interaction enables certain microorganisms to survive in various environments. pseudomonas aeruginosa is a highly adaptable bacterium that ubiquitously inhabits diverse environments including soil, marine habitats, plants and animals. behind this adaptivity, p. aeruginosa has abilities not only to outcompete others but also to communicate with each other to develop a multispecies community. in this review, we focus on how p. ...201323363620
phenotypic and genotypic characterisation of burkholderia cenocepacia j2315 mutants affected in homoserine lactone and diffusible signal factor-based quorum sensing systems suggests interplay between both types of systems.many putative virulence factors of burkholderia cenocepacia are controlled by various quorum sensing (qs) circuits. these qs systems either use n-acyl homoserine lactones (ahl) or cis-2-dodecenoic acid ("burkholderia diffusible signal factor", bdsf) as signalling molecules. previous work suggested that there is little cross-talk between both types of systems. we constructed mutants in b. cenocepacia strain j2315, in which genes encoding cepi (bcam1870), ccii (bcam0239a) and the bdsf synthase (bc ...201323383071
champacyclin, a new cyclic octapeptide from streptomyces strain c42 isolated from the baltic sea.new isolates of streptomyces champavatii were isolated from marine sediments of the gotland deep (baltic sea), from the urania basin (eastern mediterranean), and from the kiel bight (baltic sea). the isolates produced several oligopeptidic secondary metabolites, including the new octapeptide champacyclin (1a) present in all three strains. herein, we report on the isolation, structure elucidation and determination of the absolute stereochemistry of this isoleucine/leucine (ile/leu = xle) rich cyc ...201324317473
hydrogen peroxide- and nitric oxide-mediated disease control of bacterial wilt in tomato plants.reactive oxygen species (ros) generation in tomato plants by ralstonia solanacearum infection and the role of hydrogen peroxide (h2o2) and nitric oxide in tomato bacterial wilt control were demonstrated. during disease development of tomato bacterial wilt, accumulation of superoxide anion (o2 (-)) and h2o2 was observed and lipid peroxidation also occurred in the tomato leaf tissues. high doses of h2o2and sodium nitroprusside (snp) nitric oxide donor showed phytotoxicity to detached tomato leaves ...201325288967
structural insights into a novel interkingdom signaling circuit by cartography of the ligand-binding sites of the homologous quorum sensing luxr-family.recent studies have identified a novel interkingdom signaling circuit, via plant signaling molecules, and a bacterial sub-family of luxr proteins, bridging eukaryotes and prokaryotes. indeed pivotal plant-bacteria interactions are regulated by the so called plant associated bacteria (pab) luxr solo regulators that, although closely related to the quorum sensing (qs) luxr family, do not bind or respond to canonical quorum sensing n-acyl homoserine lactones (ahls), but only to specific host plant ...201324132148
identification and molecular characterization of ysal (ye3555): a novel negative regulator of ysan atpase in type three secretion system of enteropathogenic bacteria yersinia enterocolitica.type three secretion (t3s) atpases are involved in delivery of virulent factors from bacteria to their hosts (through injectisome) in an energy (atp) dependent manner during pathogenesis. the activities of these atpases are tightly controlled by their specific regulators. in yersinia enterocolitica, ysan was predicted as a putative atpase of the ysa-ysp type three secretion system (t3ss) based on sequence similarity with other t3s atpases. however detailed study and characterization of ysan and ...201324124464
characterization of maltocin p28, a novel phage tail-like bacteriocin from stenotrophomonas maltophilia.stenotrophomonas maltophilia is an important global opportunistic pathogen for which limited therapeutics are available because of the emergence of multidrug-resistant strains. a novel bacteriocin, maltocin p28, which is produced by s. maltophilia strain p28, may be the first identified phage tail-like bacteriocin from s. maltophilia. maltocin p28 resembles a contractile but nonflexible phage tail structure based on electron microscopy, and it is sensitive to trypsin, proteinase k, and heat. sds ...201323835182
sequence-based discovery of bradyrhizobium enterica in cord colitis syndrome.immunosuppression is associated with a variety of idiopathic clinical syndromes that may have infectious causes. it has been hypothesized that the cord colitis syndrome, a complication of umbilical-cord hematopoietic stem-cell transplantation, is infectious in origin.201323924002
insights into xanthomonas axonopodis pv. citri biofilm through proteomics.xanthomonas axonopodis pv. citri (x. a. pv. citri) causes citrus canker that can result in defoliation and premature fruit drop with significant production losses worldwide. biofilm formation is an important process in bacterial pathogens and several lines of evidence suggest that in x. a. pv. citri this process is a requirement to achieve maximal virulence since it has a major role in host interactions. in this study, proteomics was used to gain further insights into the functions of biofilms.201323924281
complete sequence of poz176, a 500-kilobase incp-2 plasmid encoding imp-9-mediated carbapenem resistance, from outbreak isolate pseudomonas aeruginosa 96.pseudomonas aeruginosa 96 (pa96) was isolated during a multicenter surveillance study in guangzhou, china, in 2000. whole-genome sequencing of this outbreak strain facilitated analysis of its incp-2 carbapenem-resistant plasmid, poz176. the plasmid had a length of 500,839 bp and an average percent g+c content of 57%. of the 618 predicted open reading frames, 65% encode hypothetical proteins. the poz176 backbone is not closely related to any plasmids thus far sequenced, but some similarity to pqb ...201323716048
mycorrhiza-induced resistance: more than the sum of its parts?plants can develop an enhanced defensive capacity in response to infection by arbuscular mycorrhizal fungi (amf). this 'mycorrhiza-induced resistance' (mir) provides systemic protection against a wide range of attackers and shares characteristics with systemic acquired resistance (sar) after pathogen infection and induced systemic resistance (isr) following root colonisation by non-pathogenic rhizobacteria. it is commonly assumed that fungal stimulation of the plant immune system is solely respo ...201323871659
a review on phytochemistry and ethnopharmacological aspects of genus calendula.this review includes 84 references on the genus calendula (asteraceae) and comprises ethnopharmacology, morphology and microscopy, phytoconstituents, pharmacological reports, clinical studies and toxicology of the prominent species of calendula. triterpene alcohols, triterpene saponins, flavonoids, carotenoids and polysaccharides constitute major classes of phytoconstituents of the genus. a few species of this genus have medicinal value, among these calendula officinalis linn., has been traditio ...201324347926
evolution of rep diversity: a comparative study.repetitive extragenic palindromic elements (reps) constitute a group of bacterial genomic repeats known for their high abundance and several roles in host cells´ physiology. we analyzed the phylogenetic distribution of particular rep classes in genomic sequences of sixty-three bacterial strains belonging to the pseudomonas fluorescens species complex and ten strains of stenotrophomonas sp., in order to assess intraspecific rep diversity and to gain insight into long-term rep evolution.201323758774
a novel two-component response regulator links rpf with biofilm formation and virulence of xanthomonas axonopodis pv. citri.citrus bacterial canker caused by xanthomonas axonopodis pv. citri is a serious disease that impacts citrus production worldwide, and x. axonopodis pv. citri is listed as a quarantine pest in certain countries. biofilm formation is important for the successful development of a pathogenic relationship between various bacteria and their host(s). to understand the mechanisms of biofilm formation by x. axonopodis pv. citri strain xw19, the strain was subjected to transposon mutagenesis. one mutant w ...201323626857
bean common bacterial blight: pathogen epiphytic life and effect of irrigation practices.in recent years, bean common bacterial blight (cbb) caused by xanthomonas axonopodis pv. phaseoli (xap) has caused serious yield losses in several countries. cbb is considered mainly a foliar disease in which symptoms initially appear as small water-soaked spots that then enlarge and become necrotic and usually bordered by a chlorotic zone. xap epiphytic population community has a critical role in the development of the disease and subsequent epidemics. the epiphytic population of xap in the fie ...201323539532
recruitment and rearrangement of three different genetic determinants into a conjugative plasmid increase copper resistance in pseudomonas syringae.we describe the genetic organization of a copper-resistant plasmid containing copg and cuscba genes in the plant pathogen pseudomonas syringae. chromosomal variants of czccba and a plasmid variant of cuscba were present in different p. syringae pathovar strains. transformation of the copper-sensitive pseudomonas syringae pv. syringae ff5 strain with copg or cuscba conferred copper resistance, and quantitative real-time pcr (qrt-pcr) experiments confirmed their induction by copper.201323183969
the antagonistic strain bacillus subtilis umaf6639 also confers protection to melon plants against cucurbit powdery mildew by activation of jasmonate- and salicylic acid-dependent defence responses.biological control of plant diseases has gained acceptance in recent years. bacillus subtilis umaf6639 is an antagonistic strain specifically selected for the efficient control of the cucurbit powdery mildew fungus podosphaera fusca, which is a major threat to cucurbits worldwide. the antagonistic activity relies on the production of the antifungal compounds iturin and fengycin. in a previous study, we found that umaf6639 was able to induce systemic resistance (isr) in melon and provide addition ...201323302493
identification of residues required for stalled-ribosome rescue in the codon-independent release factor yaej.the yaej protein is a codon-independent release factor with peptidyl-trna hydrolysis (pth) activity, and functions as a stalled-ribosome rescue factor in escherichia coli. to identify residues required for yaej function, we performed mutational analysis for in vitro pth activity towards rescue of ribosomes stalled on a non-stop mrna, and for ribosome-binding efficiency. we focused on residues conserved among bacterial yaej proteins. additionally, we determined the solution structure of the ggq d ...201324322300
identification of residues required for stalled-ribosome rescue in the codon-independent release factor yaej.the yaej protein is a codon-independent release factor with peptidyl-trna hydrolysis (pth) activity, and functions as a stalled-ribosome rescue factor in escherichia coli. to identify residues required for yaej function, we performed mutational analysis for in vitro pth activity towards rescue of ribosomes stalled on a non-stop mrna, and for ribosome-binding efficiency. we focused on residues conserved among bacterial yaej proteins. additionally, we determined the solution structure of the ggq d ...201324322300
hexamers of the type ii secretion atpase gspe from vibrio cholerae with increased atpase activity.the type ii secretion system (t2ss), a multiprotein machinery spanning two membranes in gram-negative bacteria, is responsible for the secretion of folded proteins from the periplasm across the outer membrane. the critical multidomain t2ss assembly atpase gspe(epse) had not been structurally characterized as a hexamer. here, four hexamers of vibrio cholerae gspe(epse) are obtained when fused to hcp1 as an assistant hexamer, as shown with native mass spectrometry. the enzymatic activity of the gs ...201323954505
argonaute protein as a linker to command center of physiological processes.micrornas (mirnas) post-transcriptionally regulate gene expression by binding to target mrnas with perfect or imperfect complementarity, recruiting an argonaute (ago) protein complex that usually results in degradation or translational repression of the target mrna. ago proteins function as the slicer enzyme in mirna and small interfering rna (sirna) pathways involved in human physiological and pathophysiological processes, such as antiviral responses and disease formation. although the past dec ...201323997530
metagenomics and novel gene discovery: promise and potential for novel therapeutics.metagenomics provides a means of assessing the total genetic pool of all the microbes in a particular environment, in a culture-independent manner. it has revealed unprecedented diversity in microbial community composition, which is further reflected in the encoded functional diversity of the genomes, a large proportion of which consists of novel genes. herein, we review both sequence-based and functional metagenomic methods to uncover novel genes and outline some of the associated problems of e ...201324317337
metagenomics and novel gene discovery: promise and potential for novel therapeutics.metagenomics provides a means of assessing the total genetic pool of all the microbes in a particular environment, in a culture-independent manner. it has revealed unprecedented diversity in microbial community composition, which is further reflected in the encoded functional diversity of the genomes, a large proportion of which consists of novel genes. herein, we review both sequence-based and functional metagenomic methods to uncover novel genes and outline some of the associated problems of e ...201324317337
structure and mechanism of the pilf dna transformation atpase from thermus thermophilus.many gram-negative bacteria contain specific systems for uptake of foreign dna, which play a critical role in the acquisition of antibiotic resistance. the ttpilf (pilf atpase from thermus thermophilus) is required for high transformation efficiency, but its mechanism of action is unknown. in the present study, we show that ttpilf is able to bind to both dna and rna. the structure of ttpilf was determined by cryoelectron microscopy in the presence and absence of the atp analogue p[nh]ppa (adenos ...201323252471
the pathochip, a functional gene array for assessing pathogenic properties of diverse microbial communities.pathogens present in the environment pose a serious threat to human, plant and animal health as evidenced by recent outbreaks. as many pathogens can survive and proliferate in the environment, it is important to understand their population dynamics and pathogenic potential in the environment. to assess pathogenic potential in diverse habitats, we developed a functional gene array, the pathochip, constructed with key virulence genes related to major virulence factors, such as adherence, colonizat ...201323765101
intrigues and intricacies of the biosynthetic pathways for the enzymatic quinocofactors: pqq, ttq, ctq, tpq, and ltq. 201324350630
intrigues and intricacies of the biosynthetic pathways for the enzymatic quinocofactors: pqq, ttq, ctq, tpq, and ltq. 201324350630
the lov protein of xanthomonas citri subsp. citri plays a significant role in the counteraction of plant immune responses during citrus canker.pathogens interaction with a host plant starts a set of immune responses that result in complex changes in gene expression and plant physiology. light is an important modulator of plant defense response and recent studies have evidenced the novel influence of this environmental stimulus in the virulence of several bacterial pathogens. xanthomonas citri subsp. citri is the bacterium responsible for citrus canker disease, which affects most citrus cultivars. the ability of this bacterium to coloni ...201324260514
identification and characterization of ribn, a novel family of riboflavin transporters from rhizobium leguminosarum and other proteobacteria.rhizobia are symbiotic bacteria able to invade and colonize the roots of legume plants, inducing the formation of nodules, where bacteria reduce atmospheric nitrogen (n2) to ammonia (nh3). riboflavin availability influences the capacity of rhizobia to survive in the rhizosphere and to colonize roots. in this study, we identified the rl1692 gene of rhizobium leguminosarum downstream of a flavin mononucleotide (fmn) riboswitch. rl1692 encodes a putative transmembrane permease with two eama domains ...201323935051
small rna-mediated regulation of host-pathogen interactions.the rise in antimicrobial drug resistance, alongside the failure of conventional research to discover new antibiotics, will inevitably lead to a public health crisis that can drastically curtail our ability to combat infectious disease. thus, there is a great global health need for development of antimicrobial countermeasures that target novel cell molecules or processes. rna represents a largely unexploited category of potential targets for antimicrobial design. for decades, control of cellular ...201323958954
global small rna chaperone hfq and regulatory small rnas are important virulence regulators in erwinia amylovora.hfq is a global small rna (srna) chaperone that interacts with hfq-regulated srnas and functions in the posttranscriptional regulation of gene expression. in this work, we identified hfq to be a virulence regulator in the gram-negative fire blight pathogen erwinia amylovora. deletion of hfq in e. amylovora ea1189 significantly reduced bacterial virulence in both immature pear fruits and apple shoots. analysis of virulence determinants in strain ea1189δhfq showed that hfq exerts pleiotropic regul ...201323378513
lysobacter enzymogenes uses two distinct cell-cell signaling systems for differential regulation of secondary-metabolite biosynthesis and colony morphology.lysobacter enzymogenes is a ubiquitous environmental bacterium that is emerging as a potentially novel biological control agent and a new source of bioactive secondary metabolites, such as the heat-stable antifungal factor (hsaf) and photoprotective polyene pigments. thus far, the regulatory mechanism(s) for biosynthesis of these bioactive secondary metabolites remains largely unknown in l. enzymogenes. in the present study, the diffusible signal factor (dsf) and diffusible factor (df)-mediated ...201323974132
evolutionary diversification and characterization of the eubacterial gene family encoding dxr type ii, an alternative isoprenoid biosynthetic enzyme.isoprenoids constitute a vast family of natural compounds performing diverse and essential functions in all domains of life. in most eubacteria, isoprenoids are synthesized through the methylerythritol 4-phosphate (mep) pathway. the production of mep is usually catalyzed by deoxyxylulose 5-phosphate reductoisomerase (dxr-i) but a few organisms use an alternative dxr-like enzyme (dxr-ii).201324004839
a practical synthesis of long-chain iso-fatty acids (iso-c12-c19) and related natural products.a gram-scale synthesis of terminally-branched iso-fatty acids (iso-c12-c19) was developed commencing with methyl undec-10-enoate (methyl undecylenate) (for iso-c12-c14) or the c15 and c16 lactones pentadecanolide (for iso-c15-c17) and hexadecanolide (for iso-c18-c19). central to the approaches outlined is the two-step construction of the terminal isopropyl group through addition of methylmagnesium bromide to the ester/lactones and selective reduction of the resulting tertiary alcohols. thus, the ...201324062846
set-domain bacterial effectors target heterochromatin protein 1 to activate host rdna transcription.transcription of rrna genes (rdnas) in the nucleolus is regulated by epigenetic chromatin modifications including histone h3 lysine (de)methylation. here we show that legas4, a legionella pneumophila type iv secretion system (tfss) effector, is targeted to specific rdna chromatin regions in the host nucleolus. legas4 promotes rdna transcription, through its set-domain (named after drosophila su(var)3-9, enhancer of zeste [e(z)], and trithorax [trx]) histone lysine methyltransferase (hkmtase) act ...201323797873
episodes of horizontal gene-transfer and gene-fusion led to co-existence of different metal-ion specific glyoxalase i.glyoxalase pathway plays an important role in stress adaptation and many clinical disorders. the first enzyme of this pathway, glyoxalase i (glxi), uses methylglyoxal as a substrate and requires either ni(ii)/co(ii) or zn(ii) for activity. here we have investigated the origin of different metal ion specificities of glxi and subsequent pattern of inheritance during evolution. our results suggest a primitive origin of single-domain ni dependent glxi [ni-glxi]. this subsequently evolved into zn act ...201324220130
antimicrobial strategies centered around reactive oxygen species--bactericidal antibiotics, photodynamic therapy, and beyond.reactive oxygen species (ros) can attack a diverse range of targets to exert antimicrobial activity, which accounts for their versatility in mediating host defense against a broad range of pathogens. most ros are formed by the partial reduction in molecular oxygen. four major ros are recognized comprising superoxide (o2•-), hydrogen peroxide (h2o2), hydroxyl radical (•oh), and singlet oxygen ((1)o2), but they display very different kinetics and levels of activity. the effects of o2•- and h2o2 ar ...201323802986
biosynthetic mechanism for sunscreens of the biocontrol agent lysobacter enzymogenes.lysobacter are ubiquitous environmental bacteria emerging as novel biocontrol agents and new sources of anti-infectives. so far, very little effort has been invested in the study of the biology of these gram-negative gliding bacteria. many lysobacter species are characterized by their yellow-orange appearance. using transposon mutagenesis, we identified a stand-alone polyketide synthase (pks) gene cluster required for the pigment production in l. enzymogenes oh11. the yellow pigments were abolis ...201323826105
function-related positioning of the type ii secretion atpase of xanthomonas campestris pv. campestris.gram-negative bacteria use the type ii secretion (t2s) system to secrete exoproteins for attacking animal or plant cells or to obtain nutrients from the environment. the system is unique in helping folded proteins traverse the outer membrane. the secretion machine comprises multiple proteins spanning the cell envelope and a cytoplasmic atpase. activity of the atpase, when copurified with the cytoplasmic domain of an interactive atpase partner, is stimulated by an acidic phospholipid, suggesting ...201323536861
roles of alkyl hydroperoxide reductase subunit c (ahpc) in viable but nonculturable vibrio parahaemolyticus.alkyl hydroperoxide reductase subunit c (ahpc) is the catalytic subunit responsible for the detoxification of reactive oxygen species that form in bacterial cells or are derived from the host; thus, ahpc facilitates the survival of pathogenic bacteria under environmental stresses or during infection. this study investigates the role of ahpc in the induction and maintenance of a viable but nonculturable (vbnc) state in vibrio parahaemolyticus. in this investigation, ahpc1 (vpa1683) and ahpc2 (vp0 ...201323563952
epidemiology of bacteremia caused by uncommon non-fermentative gram-negative bacteria.prevalence of bacteremia caused by non-fermentative gram-negative bacteria (nfgnb) has been increasing over the past decade. although many studies have already investigated epidemiology of nfgnb bacteremia, most focused only on common nfgnb including pseudomonas aeruginosa (pa) and acinetobacter baumannii (ab). knowledge of uncommon nfgnb bacteremia is very limited. our study aimed to investigate epidemiology and identify factors associated with uncommon nfgnb bacteremia.201323566113
structure-function relationships of membrane-associated gt-b glycosyltransferases.membrane-associated gt-b glycosyltransferases (gts) comprise a large family of enzymes that catalyze the transfer of a sugar moiety from nucleotide-sugar donors to a wide range of membrane-associated acceptor substrates, mostly in the form of lipids and proteins. as a consequence, they generate a significant and diverse amount of glycoconjugates in biological membranes, which are particularly important in cell-cell, cell-matrix and host-pathogen recognition events. membrane-associated gt-b enzym ...201324253765
structure-function relationships of membrane-associated gt-b glycosyltransferases.membrane-associated gt-b glycosyltransferases (gts) comprise a large family of enzymes that catalyze the transfer of a sugar moiety from nucleotide-sugar donors to a wide range of membrane-associated acceptor substrates, mostly in the form of lipids and proteins. as a consequence, they generate a significant and diverse amount of glycoconjugates in biological membranes, which are particularly important in cell-cell, cell-matrix and host-pathogen recognition events. membrane-associated gt-b enzym ...201324253765
biochemical activities of streptococcus pneumoniae serotype 2 capsular glycosyltransferases and significance of suppressor mutations affecting the initiating glycosyltransferase cps2e.the capsular polysaccharide (cps) is essential for streptococcus pneumoniae virulence. its synthesis requires multiple enzymes, and defects that block completion of the pathway can be lethal in the absence of secondary suppressor mutations. in this study, we examined the functions of three capsular glycosyltransferases (cps2f, cps2g, and cps2i) involved in serotype 2 cps synthesis, whose deletions select for secondary mutations. we demonstrate that cps2f is a rhamnosyltransferase that catalyzes ...201324097952
unique structural modifications are present in the lipopolysaccharide from colistin-resistant strains of acinetobacter baumannii.acinetobacter baumannii is a nosocomial opportunistic pathogen that can cause severe infections, including hospital-acquired pneumonia, wound infections, and sepsis. multidrug-resistant (mdr) strains are prevalent, further complicating patient treatment. due to the increase in mdr strains, the cationic antimicrobial peptide colistin has been used to treat a. baumannii infections. colistin-resistant strains of a. baumannii with alterations to the lipid a component of lipopolysaccharide (lps) have ...201323877686
a multicopper oxidase is required for copper resistance in mycobacterium tuberculosis.mycobacterium tuberculosis, the causative agent of tuberculosis, is one of the most important bacterial pathogens. recent work has revealed that the natural bactericidal properties of copper are utilized by the host immune system to combat infections with bacteria, including m. tuberculosis. however, m. tuberculosis employs multiple mechanisms to reduce the internal copper amount by efflux and sequestration, which are required for virulence of m. tuberculosis. here, we describe an alternative me ...201323772064
allelic variation in two distinct pseudomonas syringae flagellin epitopes modulates the strength of plant immune responses but not bacterial motility.the bacterial flagellin (flic) epitopes flg22 and flgii-28 are microbe-associated molecular patterns (mamps). although flg22 is recognized by many plant species via the pattern recognition receptor fls2, neither the flgii-28 receptor nor the extent of flgii-28 recognition by different plant families is known. here, we tested the significance of flgii-28 as a mamp and the importance of allelic diversity in flg22 and flgii-28 in plant-pathogen interactions using purified peptides and a pseudomonas ...201323865782
short and long-term genome stability analysis of prokaryotic genomes.gene organization dynamics is actively studied because it provides useful evolutionary information, makes functional annotation easier and often enables to characterize pathogens. there is therefore a strong interest in understanding the variability of this trait and the possible correlations with life-style. two kinds of events affect genome organization: on one hand translocations and recombinations change the relative position of genes shared by two genomes (i.e. the backbone gene order); on ...201323651581
intracellularly induced cyclophilins play an important role in stress adaptation and virulence of brucella abortus.brucella is an intracellular bacterial pathogen that causes the worldwide zoonotic disease brucellosis. brucella virulence relies on its ability to transition to an intracellular lifestyle within host cells. thus, this pathogen must sense its intracellular localization and then reprogram gene expression for survival within the host cell. a comparative proteomic investigation was performed to identify differentially expressed proteins potentially relevant for brucella intracellular adaptation. tw ...201323230297
genomic analysis of melioribacter roseus, facultatively anaerobic organotrophic bacterium representing a novel deep lineage within bacteriodetes/chlorobi group.melioribacter roseus is a moderately thermophilic facultatively anaerobic organotrophic bacterium representing a novel deep branch within bacteriodetes/chlorobi group. to better understand the metabolic capabilities and possible ecological functions of m. roseus and get insights into the evolutionary history of this bacterial lineage, we sequenced the genome of the type strain p3m-2(t). a total of 2838 open reading frames was predicted from its 3.30 mb genome. the whole proteome analysis support ...201323301019
the role of bacterial biofilms and surface components in plant-bacterial associations.the role of bacterial surface components in combination with bacterial functional signals in the process of biofilm formation has been increasingly studied in recent years. plants support a diverse array of bacteria on or in their roots, transport vessels, stems, and leaves. these plant-associated bacteria have important effects on plant health and productivity. biofilm formation on plants is associated with symbiotic and pathogenic responses, but how plants regulate such associations is unclear ...201323903045
a genomic survey of reb homologs suggests widespread occurrence of r-bodies in proteobacteria.bacteria and eukaryotes are involved in many types of interaction in nature, with important ecological consequences. however, the diversity, occurrence, and mechanisms of these interactions often are not fully known. the obligate bacterial endosymbionts of paramecium provide their hosts with the ability to kill sensitive paramecium strains through the production of r-bodies, highly insoluble coiled protein ribbons. r-bodies have been observed in a number of free-living bacteria, where their func ...201323450193
exploiting quorum sensing to confuse bacterial pathogens.cell-cell communication, or quorum sensing, is a widespread phenomenon in bacteria that is used to coordinate gene expression among local populations. its use by bacterial pathogens to regulate genes that promote invasion, defense, and spread has been particularly well documented. with the ongoing emergence of antibiotic-resistant pathogens, there is a current need for development of alternative therapeutic strategies. an antivirulence approach by which quorum sensing is impeded has caught on as ...201323471618
heterologous expression of mycobacterial esx complexes in escherichia coli for structural studies is facilitated by the use of maltose binding protein fusions.the expression of heteroligomeric protein complexes for structural studies often requires a special coexpression strategy. the reason is that the solubility and proper folding of each subunit of the complex requires physical association with other subunits of the complex. the genomes of pathogenic mycobacteria encode many small protein complexes, implicated in bacterial fitness and pathogenicity, whose characterization may be further complicated by insolubility upon expression in escherichia col ...201324312350
crystal structure of an hd-gyp domain cyclic-di-gmp phosphodiesterase reveals an enzyme with a novel trinuclear catalytic iron centre.bis-(3',5') cyclic di-guanylate (c-di-gmp) is a key bacterial second messenger that is implicated in the regulation of many crucial processes that include biofilm formation, motility and virulence. cellular levels of c-di-gmp are controlled through synthesis by ggdef domain diguanylate cyclases and degradation by two classes of phosphodiesterase with eal or hd-gyp domains. here, we have determined the structure of an enzymatically active hd-gyp domain protein from persephonella marina (pmgh) alo ...201324176013
crystal structure of an hd-gyp domain cyclic-di-gmp phosphodiesterase reveals an enzyme with a novel trinuclear catalytic iron centre.bis-(3',5') cyclic di-guanylate (c-di-gmp) is a key bacterial second messenger that is implicated in the regulation of many crucial processes that include biofilm formation, motility and virulence. cellular levels of c-di-gmp are controlled through synthesis by ggdef domain diguanylate cyclases and degradation by two classes of phosphodiesterase with eal or hd-gyp domains. here, we have determined the structure of an enzymatically active hd-gyp domain protein from persephonella marina (pmgh) alo ...201324176013
c-di-gmp hydrolysis by pseudomonas aeruginosa hd-gyp phosphodiesterases: analysis of the reaction mechanism and novel roles for pgpg.in biofilms, the bacterial community optimizes the strategies to sense the environment and to communicate from cell to cell. a key player in the development of a bacterial biofilm is the second messenger c-di-gmp, whose intracellular levels are modulated by the opposite activity of diguanylate cyclases and phosphodiesterases. given the huge impact of bacterial biofilms on human health, understanding the molecular details of c-di-gmp metabolism represents a critical step in the development of nov ...201324066157
cyclic di-gmp signalling and the regulation of bacterial virulence.signal transduction pathways involving the second messenger cyclic di-gmp [bis-(3'-5')-cyclic di-guanosine monophosphate] occur widely in bacteria where they act to link perception of environmental or intracellular cues and signals to specific alterations in cellular function. such alterations can contribute to bacterial lifestyle transitions including biofilm formation and virulence. the cellular levels of the nucleotide are controlled through the opposing activities of diguanylate cyclases (dg ...201323704785
cyclic di-gmp: the first 25 years of a universal bacterial second messenger.twenty-five years have passed since the discovery of cyclic dimeric (3'→5') gmp (cyclic di-gmp or c-di-gmp). from the relative obscurity of an allosteric activator of a bacterial cellulose synthase, c-di-gmp has emerged as one of the most common and important bacterial second messengers. cyclic di-gmp has been shown to regulate biofilm formation, motility, virulence, the cell cycle, differentiation, and other processes. most c-di-gmp-dependent signaling pathways control the ability of bacteria t ...201323471616
functional screening of metagenome and genome libraries for detection of novel flavonoid-modifying enzymes.the functional detection of novel enzymes other than hydrolases from metagenomes is limited since only a very few reliable screening procedures are available that allow the rapid screening of large clone libraries. for the discovery of flavonoid-modifying enzymes in genome and metagenome clone libraries, we have developed a new screening system based on high-performance thin-layer chromatography (hptlc). this metagenome extract thin-layer chromatography analysis (meta) allows the rapid detection ...201323686272
isolation of rhizospheric and roots endophytic actinomycetes from leguminosae plant and their activities to inhibit soybean pathogen, xanthomonas campestris pv. glycine.in this study, actinomycetes from roots and rhizospheric soils of leguminous plants were isolated using starch casein agar supplemented with antifungal and antibacterial antibiotics. three hundred and seventeen actinomycetes were isolated with 77 isolates obtained from plant roots and 240 isolates from rhizospheric soils. analysis of whole-organism hydrolysates showed that 289 strains were rich in the ll-isomer of diaminopimelic acid, a result consistent with their assignment to the streptomycet ...201323913026
identification of a histidine metal ligand in the arge-encoded n-acetyl-l-ornithine deacetylase from escherichia coli.the h355a, h355k, h80a, and h80k mutant enzymes of the arge-encoded n-acetyl-l-ornithine deacetylase (arge) from escherichia coli were prepared, however, only the h355a enzyme was found to be soluble. kinetic analysis of the co(ii)-loaded h355a exhibited activity levels that were 380-fold less than co(ii)-loaded wt arge. electronic absorption spectra of co(ii)-loaded h355a-arge indicate that the bound co(ii) ion resides in a distorted, five-coordinate environment and isothermal titration calorim ...201325674394
agrobacterium infection and plant defense-transformation success hangs by a thread.the value of agrobacterium tumefaciens for plant molecular biologists cannot be appreciated enough. this soil-borne pathogen has the unique capability to transfer dna (t-dna) into plant systems. gene transfer involves both bacterial and host factors, and it is the orchestration of these factors that determines the success of transformation. some plant species readily accept integration of foreign dna, while others are recalcitrant. the timing and intensity of the microbially activated host defen ...201324391655
prophage-mediated dynamics of 'candidatus liberibacter asiaticus' populations, the destructive bacterial pathogens of citrus huanglongbing.prophages are highly dynamic components in the bacterial genome and play an important role in intraspecies variations. there are at least two prophages in the chromosomes of candidatus liberibacter asiaticus' (las) floridian isolates. las is both unculturable and the most prevalent species of liberibacter pathogens that cause huanglongbing (hlb), a worldwide destructive disease of citrus. in this study, seven new prophage variants resulting from two hyper-variable regions were identified by scre ...201324349235
a high-throughput virus-induced gene silencing protocol identifies genes involved in multi-stress tolerance.understanding the function of a particular gene under various stresses is important for engineering plants for broad-spectrum stress tolerance. although virus-induced gene silencing (vigs) has been used to characterize genes involved in abiotic stress tolerance, currently available gene silencing and stress imposition methodology at the whole plant level is not suitable for high-throughput functional analyses of genes. this demands a robust and reliable methodology for characterizing genes invol ...201324289810
genomic survey of pathogenicity determinants and vntr markers in the cassava bacterial pathogen xanthomonas axonopodis pv. manihotis strain cio151.xanthomonas axonopodis pv. manihotis (xam) is the causal agent of bacterial blight of cassava, which is among the main components of human diet in africa and south america. current information about the molecular pathogenicity factors involved in the infection process of this organism is limited. previous studies in other bacteria in this genus suggest that advanced draft genome sequences are valuable resources for molecular studies on their interaction with plants and could provide valuable too ...201324278159
a comparative hidden markov model analysis pipeline identifies proteins characteristic of cereal-infecting fungi.fungal pathogens cause devastating losses in economically important cereal crops by utilising pathogen proteins to infect host plants. secreted pathogen proteins are referred to as effectors and have thus far been identified by selecting small, cysteine-rich peptides from the secretome despite increasing evidence that not all effectors share these attributes.201324252298
tomato fruit and seed colonization by clavibacter michiganensis subsp. michiganensis through external and internal routes.the gram-positive bacterium clavibacter michiganensis subsp. michiganensis, causal agent of bacterial wilt and canker of tomato, is an economically devastating pathogen that inflicts considerable damage throughout all major tomato-producing regions. annual outbreaks continue to occur in new york, where c. michiganensis subsp. michiganensis spreads via infected transplants, trellising stakes, tools, and/or soil. globally, new outbreaks can be accompanied by the introduction of contaminated seed s ...201324014525
antimicrobial nodule-specific cysteine-rich peptides induce membrane depolarization-associated changes in the transcriptome of sinorhizobium meliloti.leguminous plants establish symbiosis with nitrogen-fixing alpha- and betaproteobacteria, collectively called rhizobia, which provide combined nitrogen to support plant growth. members of the inverted repeat-lacking clade of legumes impose terminal differentiation on their endosymbiotic bacterium partners with the help of the nodule-specific cysteine-rich (ncr) peptide family composed of close to 600 members. among the few tested ncr peptides, cationic ones had antirhizobial activity measured by ...201323995935
bacterial effector activates jasmonate signaling by directly targeting jaz transcriptional repressors.gram-negative bacterial pathogens deliver a variety of virulence proteins through the type iii secretion system (t3ss) directly into the host cytoplasm. these type iii secreted effectors (t3ses) play an essential role in bacterial infection, mainly by targeting host immunity. however, the molecular basis of their functionalities remains largely enigmatic. here, we show that the pseudomonas syringae t3se hopz1a, a member of the widely distributed yopj effector family, directly interacts with jasm ...201324204266
the current status of the elemental defense hypothesis in relation to pathogens.metal hyperaccumulating plants are able to accumulate exceptionally high concentrations of metals, such as zinc, nickel, or cadmium, in their aerial tissues. these metals reach concentrations that would be toxic to most other plant species. this trait has evolved multiple times independently in the plant kingdom. recent studies have provided new insight into the ecological and evolutionary significance of this trait, by showing that some metal hyperaccumulating plants can use high concentrations ...201324137169
small rna sx13: a multifaceted regulator of virulence in the plant pathogen xanthomonas.small noncoding rnas (srnas) are ubiquitous posttranscriptional regulators of gene expression. using the model plant-pathogenic bacterium xanthomonas campestris pv. vesicatoria (xcv), we investigated the highly expressed and conserved srna sx13 in detail. deletion of sx13 impinged on xcv virulence and the expression of genes encoding components and substrates of the hrp type iii secretion (t3s) system. qrt-pcr analyses revealed that sx13 promotes mrna accumulation of hrpx, a key regulator of the ...201324068933
vigs-mediated forward genetics screening for identification of genes involved in nonhost resistance.nonhost disease resistance of plants against bacterial pathogens is controlled by complex defense pathways. understanding this mechanism is important for developing durable disease-resistant plants against wide range of pathogens. virus-induced gene silencing (vigs)-based forward genetics screening is a useful approach for identification of plant defense genes imparting nonhost resistance. tobacco rattle virus (trv)-based vigs vector is the most efficient vigs vector to date and has been efficie ...201323995956
loss of function in mlo orthologs reduces susceptibility of pepper and tomato to powdery mildew disease caused by leveillula taurica.powdery mildew disease caused by leveillula taurica is a serious fungal threat to greenhouse tomato and pepper production. in contrast to most powdery mildew species which are epiphytic, l. taurica is an endophytic fungus colonizing the mesophyll tissues of the leaf. in barley, arabidopsis, tomato and pea, the correct functioning of specific homologues of the plant mlo gene family has been found to be required for pathogenesis of epiphytic powdery mildew fungi. the aim of this study was to inves ...201323923019
overexpression of atshn1/win1 provokes unique defense responses.the plant cell cuticle serves as the first barrier protecting plants from mechanical injury and invading pathogens. the cuticle can be breached by cutinase-producing pathogens and the degradation products may activate pathogenesis signals in the invading pathogens. cuticle degradation products may also trigger the plant's defense responses. botrytis cinerea is an important plant pathogen, capable of attacking and causing disease in a wide range of plant species. arabidopsis thaliana shn1-1d is a ...201323922943
the salmonella type iii effector ssph2 specifically exploits the nlr co-chaperone activity of sgt1 to subvert immunity.to further its pathogenesis, s. typhimurium delivers effector proteins into host cells, including the novel e3 ubiquitin ligase (nel) effector ssph2. using model systems in a cross-kingdom approach we gained further insight into the molecular function of this effector. here, we show that ssph2 modulates innate immunity in both mammalian and plant cells. in mammalian cell culture, ssph2 significantly enhanced nod1-mediated il-8 secretion when transiently expressed or bacterially delivered. in add ...201323935490
receptor-like cytoplasmic kinases are pivotal components in pattern recognition receptor-mediated signaling in plant immunity.innate immunity is generally initiated with recognition of conserved pathogen-associated molecular patterns (pamps). pamps are perceived by pattern recognition receptors (prrs), leading to activation of a series of immune responses, including the expression of defense genes, ros production and activation of map kinase. recent progress has indicated that receptor-like cytoplasmic kinases (rlcks) are directly activated by ligand-activated prrs and initiate pattern-triggered immunity (pti) in both ...201323857358
modulation of phytoalexin biosynthesis in engineered plants for disease resistance.phytoalexins are antimicrobial substances of low molecular weight produced by plants in response to infection or stress, which form part of their active defense mechanisms. starting in the 1950's, research on phytoalexins has begun with biochemistry and bio-organic chemistry, resulting in the determination of their structure, their biological activity as well as mechanisms of their synthesis and their catabolism by microorganisms. elucidation of the biosynthesis of numerous phytoalexins has perm ...201323880860
the receptor-like protein remax of arabidopsis detects the microbe-associated molecular pattern emax from xanthomonas.as part of their immune system, plants have pattern recognition receptors (prrs) that can detect a broad range of microbe-associated molecular patterns (mamps). here, we identified a prr of arabidopsis thaliana with specificity for the bacterial mamp emax from xanthomonads. response to emax seems to be restricted to the brassicaceae family and also varied among different accessions of arabidopsis. in crosses between sensitive accessions and the insensitive accession shakhdara, emax perception ma ...201323898033
pepper arginine decarboxylase is required for polyamine and γ-aminobutyric acid signaling in cell death and defense response.the xanthomonas campestris pv vesicatoria (xcv) effector avrbst induces a hypersensitive cell death in pepper (capsicum annuum). however, the molecular mechanisms underlying avrbst-triggered cell death are not fully understood. here, we identified pepper arginine decarboxylase (caadc1) as an avrbst-interacting protein, which is early and strongly induced in incompatible pepper-xcv interactions. bimolecular fluorescence complementation and coimmunoprecipitation assays showed that the caadc1-avrbs ...201323784462
oxylipin biosynthesis genes positively regulate programmed cell death during compatible infections with the synergistic pair potato virus x-potato virus y and tomato spotted wilt virus.one of the most severe symptoms caused by compatible plant-virus interactions is systemic necrosis, which shares common attributes with the hypersensitive response to incompatible pathogens. although several studies have identified viral symptom determinants responsible for systemic necrosis, mechanistic models of how they contribute to necrosis in infected plants remain scarce. here, we examined the involvement of different branches of the oxylipin biosynthesis pathway in the systemic necrosis ...201323487466
the pseudomonas syringae type iii effector avrrpt2 promotes pathogen virulence via stimulating arabidopsis auxin/indole acetic acid protein turnover.to accomplish successful infection, pathogens deploy complex strategies to interfere with host defense systems and subvert host physiology to favor pathogen survival and multiplication. modulation of plant auxin physiology and signaling is emerging as a common virulence strategy for phytobacteria to cause diseases. however, the underlying mechanisms remain largely elusive. we have previously shown that the pseudomonas syringae type iii effector avrrpt2 alters arabidopsis (arabidopsis thaliana) a ...201323632856
suppression of plant defense responses by extracellular metabolites from pseudomonas syringae pv. tabaci in nicotiana benthamiana.pseudomonas syringae pv. tabaci (pstab) is the causal agent of wildfire disease in tobacco plants. several pathovars of pseudomonas syringae produce a phytotoxic extracellular metabolite called coronatine (cor). cor has been shown to suppress plant defense responses. interestingly, pstab does not produce cor but still actively suppresses early plant defense responses. it is not clear if pstab produces any extracellular metabolites that actively suppress early defense during bacterial pathogenesi ...201323597256
modifying lignin to improve bioenergy feedstocks: strengthening the barrier against pathogens?lignin is a ubiquitous polymer present in cell walls of all vascular plants, where it rigidifies and strengthens the cell wall structure through covalent cross-linkages to cell wall polysaccharides. the presence of lignin makes the cell wall recalcitrant to conversion into fermentable sugars for bioenergy uses. therefore, reducing lignin content and modifying its linkages have become major targets for bioenergy feedstock development through either biotechnology or traditional plant breeding. in ...201323577013
diatom assemblages promote ice formation in large lakes.we present evidence for the directed formation of ice by planktonic communities dominated by filamentous diatoms sampled from the ice-covered laurentian great lakes. we hypothesize that ice formation promotes attachment of these non-motile phytoplankton to overlying ice, thereby maintaining a favorable position for the diatoms in the photic zone. however, it is unclear whether the diatoms themselves are responsible for ice nucleation. scanning electron microscopy revealed associations of bacteri ...201323552624
escherichia coli o157:h7 induces stronger plant immunity than salmonella enterica typhimurium sl1344.consumption of fresh produce contaminated with bacterial human pathogens has resulted in various, sometimes deadly, disease outbreaks. in this study, we assessed plant defense responses induced by the fully pathogenic bacteria escherichia coli o157:h7 and salmonella enterica serovar typhimurium sl1344 in both arabidopsis thaliana and lettuce (lactuca sativa). unlike sl1344, o157:h7 induced strong plant immunity at both pre-invasion and post-invasion steps of infection. for instance, o157:h7 trig ...201323301812
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