- Volume 161, Issue 4, 2015
Volume 161, Issue 4, 2015
- Reviews
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Resistance to bacteriocins produced by Gram-positive bacteria
More LessBacteriocins are prokaryotic proteins or peptides with antimicrobial activity. Most of them exhibit a broad spectrum of activity, inhibiting micro-organisms belonging to different genera and species, including many bacterial pathogens which cause human, animal or plant infections. Therefore, these substances have potential biotechnological applications in either food preservation or prevention and control of bacterial infectious diseases. However, there is concern that continuous exposure of bacteria to bacteriocins may select cells resistant to them, as observed for conventional antimicrobials. Based on the models already investigated, bacteriocin resistance may be either innate or acquired and seems to be a complex phenomenon, arising at different frequencies (generally from 10−9 to 10−2) and by different mechanisms, even amongst strains of the same bacterial species. In the present review, we discuss the prevalence, development and molecular mechanisms involved in resistance to bacteriocins produced by Gram-positive bacteria. These mechanisms generally involve changes in the bacterial cell envelope, which result in (i) reduction or loss of bacteriocin binding or insertion, (ii) bacteriocin sequestering, (iii) bacteriocin efflux pumping (export) and (iv) bacteriocin degradation, amongst others. Strategies that can be used to overcome this resistance are also addressed.
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- Cell and Molecular Biology of Microbes
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A lactose fermentation product produced by Lactococcus lactis subsp. lactis, acetate, inhibits the motility of flagellated pathogenic bacteria
More LessMany strains of lactic acid bacteria have been used for the production of probiotics. Some metabolites produced by lactic acid bacteria impair the motilities of pathogenic bacteria. Because bacterial motility is strongly associated with virulence, the metabolic activities of lactic acid bacteria are effective for suppressing bacterial infections. Here we show that lactose fermentation by Lactococcus lactis subsp. lactis inhibits the motility of Salmonella enterica serovar Typhimurium. A single-cell tracking and rotation assay for a single flagellum showed that the swimming behaviour of Salmonella was severely but transiently impaired through disruption of flagellar rotation on exposure to media cultivated with Lac . lactis. Using a pH-sensitive fluorescent protein, we observed that the intracellular pH of Salmonella was decreased because of some fermentation products of Lac. lactis. We identified acetate as the lactose fermentation product of Lac. lactis triggering the paralysis of Salmonella flagella. The motilities of Pseudomonas, Vibrio and Leptospira strains were also severely disrupted by lactose utilization by Lac. lactis. These results highlight the potential use of Lac. lactis for preventing infections by multiple bacterial species.
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Effect of iron on the probiotic properties of the vaginal isolate Lactobacillus jensenii CECT 4306
The vaginal microbiota of healthy, fertile women is dominated by lactobacilli. As a defence mechanism, these bacteria produce H2O2 to discourage colonization of the vagina by undesirable micro-organisms. In particular, Lactobacillus jensenii CECT 4306 is a strong producer of H2O2 and has been found to protect itself from the bactericidal effects of this compound through the activity of extracellular peroxidases. However, this peroxidase activity is dependent on the presence of Fe3+, which is found in elevated concentrations in the vaginal mucosa as a consequence of the menstrual discharge. The aim of the present work was to evaluate whether Fe3+ is able to modulate other potential probiotic properties of strain 4306. We found that Fe3+ enhances the adhesion of L. jensenii CECT 4306 to mucin and to HT-29 and HT-29 MTX cells, and, in addition, improves the anti-inflammatory profile, as judged by an increase in the ratio of IL-10/IL-12p70 that were secreted by macrophages. A comparison of total, secreted and surface proteins produced in the presence and absence of Fe3+ revealed significant differences in the concentration of the moonlighting protein glyceraldehyde-3-phosphate dehydrogenase (GAPDH). In conclusion, Fe3+ seems to improve the probiotic characteristics of L. jensenii CECT 4306, and future research of the interactions of this strain with its vaginal environment may reveal further information about different aspects of its probiotic potential.
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Transcription and translation of the rpsJ, rplN and rRNA operons of the tubercle bacillus
Several species of the genus Mycobacterium are human pathogens, notably the tubercle bacillus (Mycobacterium tuberculosis). The rate of proliferation of a bacterium is reflected in the rate of ribosome synthesis. This report describes a quantitative analysis of the early stages of the synthesis of ribosomes of M. tuberculosis. Specifically, the roles of three large operons, namely: the rrn operon (1.7 microns) encoding rrs (16S rRNA), rrl (23S rRNA) and rrf (5S rRNA); the rpsJ operon (1.93 microns), which encodes 11 ribosomal proteins; and the rplN operon (1.45 microns), which encodes 10 ribosomal proteins. A mathematical framework based on properties of population-average cells was developed to identify the number of transcripts of the rpsJ and rplN operons needed to maintain exponential growth. The values obtained were supported by RNaseq data. The motif 5′-gcagac-3′ was found close to 5′ end of transcripts of mycobacterial rplN operons, suggesting it may form part of the RpsH feedback binding site because the same motif is present in the ribosome within the region of rrs that forms the binding site for RpsH.
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Cooperative regulation of the common target genes between H2O2-sensing YedVW and Cu2+-sensing CusSR in Escherichia coli
More LessYedVW is one of the uncharacterized two-component systems (TCSs) of Escherichia coli. In order to identify the regulation targets of YedVW, we performed genomic SELEX (systematic evolution of ligands by exponential enrichment) screening using phosphorylated YedW and an E. coli DNA library, and identified YedW-binding sites within three intergenic spacers, yedW–hiuH, cyoA–ampG and cusR–cusC, along the E. coli genome. Using a reporter assay system, we found that transcription of hiuH, encoding 5-hydroxyisourate hydrolase, was induced at high concentrations of either Cu2+ or H2O2. Cu2+-dependent expression of hiuH was observed in the yedWV knockout mutant, but was reduced markedly in the cusRS-null mutant. However, H2O2-induced hiuH expression was observed in the cusRS-null mutant, but not in the yedWV-null mutant. Gel mobility shift and DNase I footprinting analyses showed binding of both YedW and CusR to essentially the same sequence within the hiuH promoter region. Taken together, we concluded that YedVW and CusSR formed a unique cooperative TCS pair by recognizing and regulating the same targets, but under different environmental conditions – YedVW played a role in H2O2 response regulation, whilst CusSR played a role in Cu2+ response regulation.
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The pleiotropic transcriptional response of Mycobacterium tuberculosis to vitamin C is robust and overlaps with the bacterial response to multiple intracellular stresses
Mycobacterium tuberculosis (Mtb) owes its success as a pathogen in large measure to its ability to exist in a persistent state of ‘dormancy’ resulting in a lifelong latent tuberculosis (TB) infection. An understanding of bacterial adaptation during dormancy will help in devising approaches to counter latent TB infection. In vitro models have provided valuable insights into bacterial adaptation; however, they have limitations because they do not disclose the bacterial response to the intracellular environment wherein the bacteria are simultaneously exposed to multiple stresses. We describe the pleiotropic response of Mtb in the vitamin C (vit C) model of dormancy developed in our laboratory. Vit C mediates a rapid regulation of genes representing ~14 % of the genome in Mtb cultures. The upregulated genes were better represented in lipid, intermediary metabolism and regulatory protein categories. The downregulated genes mainly related to virulence, detoxification, information pathways and cell wall processes. A comparison of this response to that in other models indicates that vit C generates a multiple-stress environment for axenic Mtb cultures that resembles a macrophage-like environment. The bacterial response to vit C resembles responses to gaseous stresses such as hypoxia and nitric oxide, oxidative and nitrosative stresses, nutrient starvation and, notably, the activated macrophage environment itself. These responses demonstrate that the influence of vit C on Mtb gene expression extends well beyond the DevR dormancy regulon. A detailed characterization of the response to vit C is expected to disclose useful strategies to counter the adaptive mechanisms essential to Mtb dormancy.
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EF0176 and EF0177 from Enterococcus faecalis V583 are substrate-binding lipoproteins involved in ABC transporter mediated ribonucleoside uptake
More LessOne of the ABC transporter systems in Enterococcus faecalis V583 is encoded by the ef0176–ef0180 gene cluster, which differs from orthologous operons in related bacteria in that it contains two genes putatively encoding substrate-binding proteins (SBPs). These SBPs, EF0176 and EF0177, have previously been identified on the surface of E. faecalis. By phenotypic studies of single and double knockout mutants, we show here that EF0176 and EF0177 are specific for ribonucleosides and, by inference, that the EF0176–EF0180 ABC transporter plays a role in nucleoside uptake. The specificity of the SBPs was mapped using growth experiments on a medium, RPMI 1640, that only supports growth of E. faecalis when supplemented with purine nucleosides or their corresponding bases. This analysis was complemented by studies with toxic fluorinated pyrimidine ribonucleoside analogues and competition experiments. The data show that EF0176 and EF0177 have broad and overlapping, but not identical, substrate specificities and that they, together, are likely to bind and facilitate the transport of all common ribonucleosides. Comparative sequence analysis and inspection of an available crystal structure of an orthologue, PnrA from Treponema pallidum, showed that the strongest binding interactions between the protein and the ligand involve the ribose moiety and that sequence variation in the binding site primarily affects interactions with the base. This explains both the broad substrate specificity of these binding proteins and the observed variations therein. The presence of two SBPs in this nucleoside ABC transporter system in E. faecalis may improve the bacterium’s ability to scavenge nucleosides.
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Mycobacterium tuberculosis H37Rv has a single nucleotide polymorphism in PhoR which affects cell wall hydrophobicity and gene expression
More LessMycobacterium tuberculosis is a successful pathogen that can adapt to multiple environmental niches. As part of its repertoire of adaptive responses, two-component regulatory systems play a major role in co-ordinating gene expression at the global level. The PhoPR system controls major cellular functions, including respiration, lipid metabolism, the immediate and enduring hypoxic responses, stress responses and persistence. We identified a single nucleotide polymorphism (SNP) found in the sensor kinase (PhoR) of this system between two commonly used strains of M. tuberculosis, H37Rv (PhoRP152) and CDC1551 (PhoRL152). We constructed an isogenic strain of H37Rv carrying PhoRL152, as well as strains containing two different copies of the PhoPR locus, to determine the functional consequences of the SNP on phenotypic traits. The previously identified Apr locus was not acid-inducible in H37Rv, although it was in the CDC1551 strain. Surprisingly, the acid-responsive expression was not completely dependent on the PhoR SNP, and the locus remained constitutively expressed even in the isogenic strain H37Rv:PhoRL152. The pattern of expression in PhoPR merodiploid strains was more complex, with neither allele showing dominance. This suggests that Apr regulation is more complex than previously thought and that additional factors must be responsible for Apr upregulation in response to acid conditions. In contrast, differences we identified in cell hydrophobicity between the two strains were wholly dependent on PhoR, confirming its role as major regulator of cell wall composition. Thus the SNP in the sensor kinase has functional consequences which account for some of the differences between widely used laboratory strains.
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- [Cell and Molecular Biology of Microbes, Editor's Choice]
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Mutational analysis of the major periplasmic loops of Shigella flexneri Wzy: identification of the residues affecting O antigen modal chain length control, and Wzz-dependent polymerization activity
The O antigen (Oag) component of LPS is a major Shigella flexneri virulence determinant. Oag is polymerized by WzySf, and its modal chain length is determined by WzzSf and WzzpHS2. Site-directed mutagenesis was performed on wzySf in pWaldo-wzySf -TEV-GFP to alter Arg residues in WzySf’s two large periplasmic loops (PLs) (PL3 and PL5). Analysis of the LPS profiles conferred by mutated WzySf proteins in the wzySf deficient (Δwzy) strain identified residues that affect WzySf activity. The importance of the guanidium group of the Arg residues was investigated by altering the Arg residues to Lys and Glu, which generated WzySf mutants conferring altered LPS Oag modal chain lengths. The dependence of these WzySf mutants on WzzSf was investigated by expressing them in a wzySf and wzzSf deficient (Δwzy Δ wzz) strain. Comparison of the LPS profiles identified a role for the Arg residues in the association of WzySf and WzzSf during Oag polymerization. Colicin E2 and bacteriophage Sf6c susceptibility supported this conclusion. Comparison of the expression levels of different mutant WzySf-GFPs with the wild-type WzySf-GFP showed that certain Arg residues affected production levels of WzySf in a WzzSf-dependent manner. To our knowledge, this is the first report of S. flexneri WzySf mutants having an effect on LPS Oag modal chain length, and identified functionally significant Arg residues in WzySf.
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Mutational analysis of the major periplasmic loops of Shigella flexneri Wzy: identification of the residues affecting O antigen modal chain length control, and Wzz-dependent polymerization activity
The O antigen (Oag) component of LPS is a major Shigella flexneri virulence determinant. Oag is polymerized by WzySf, and its modal chain length is determined by WzzSf and WzzpHS2. Site-directed mutagenesis was performed on wzySf in pWaldo-wzySf -TEV-GFP to alter Arg residues in WzySf’s two large periplasmic loops (PLs) (PL3 and PL5). Analysis of the LPS profiles conferred by mutated WzySf proteins in the wzySf deficient (Δwzy) strain identified residues that affect WzySf activity. The importance of the guanidium group of the Arg residues was investigated by altering the Arg residues to Lys and Glu, which generated WzySf mutants conferring altered LPS Oag modal chain lengths. The dependence of these WzySf mutants on WzzSf was investigated by expressing them in a wzySf and wzzSf deficient (Δwzy Δ wzz) strain. Comparison of the LPS profiles identified a role for the Arg residues in the association of WzySf and WzzSf during Oag polymerization. Colicin E2 and bacteriophage Sf6c susceptibility supported this conclusion. Comparison of the expression levels of different mutant WzySf-GFPs with the wild-type WzySf-GFP showed that certain Arg residues affected production levels of WzySf in a WzzSf-dependent manner. To our knowledge, this is the first report of S. flexneri WzySf mutants having an effect on LPS Oag modal chain length, and identified functionally significant Arg residues in WzySf.
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- Cell and Molecular Biology of Microbes
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Lack of intracellular trehalose affects formation of Escherichia coli persister cells
Persisters are dormant antibiotic-tolerant cells that usually compose a small fraction of bacterial populations. In this work, we focused on the role of trehalose in persister formation. We found that the ΔotsA mutant, which is unable to synthesize trehalose, produced increased levels of persisters in the early stationary phase and under heat stress conditions. The lack of trehalose in the ΔotsA mutant resulted in oxidative stress, manifested by increased membrane lipid peroxidation after heat shock. Stationary ΔotsA cells additionally exhibited increased levels of oxidized proteins and apurinic/apyrimidinic sites in DNA as compared to WT cells. Oxidative stress caused by the lack of trehalose was accompanied by the overproduction of extracellular indole, a signal molecule that has been shown to stimulate persister formation. Our major conclusion is that intracellular trehalose protects E. coli cells against oxidative stress and limits indole synthesis, which in turn inhibits the formation of persisters.
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RNases J1 and J2 are critical pleiotropic regulators in Streptococcus mutans
More LessIn recent years, it has become increasingly evident that post-transcriptional control mechanisms are the principal source of gene regulation for a large number of prokaryotic genetic pathways, particularly those involved in virulence and environmental adaptation. Post-transcriptional regulation is largely governed by RNA stability, which itself is determined by target accessibility to RNase degradation. In most Firmicutes species, mRNA stability is strongly impacted by the activity of two recently discovered RNases referred to as RNase J1 and RNase J2. Little is known about RNase J1 function in bacteria and even less is known about RNase J2. In the current study, we mutated both RNase J orthologues in Streptococcus mutans to determine their functional roles in the cell. Single and double RNase J mutants were viable, but grew very slowly on agar plates. All of the mutants shared substantial defects in growth, morphology, acid tolerance, natural competence and biofilm formation. However, most of these defects were more severe in the RNase J2 mutant. Phenotypic suppression results also implicate a role for RNase J2 as a regulator of RNase J1 function. Unlike Bacillus subtilis, RNase J2 is a major pleiotropic regulator in S. mutans, which indicates some fundamental differences from B. subtilis in global gene regulation. Key conserved residues among the RNase J2 orthologues of lactic acid bacteria may hint at a greater role for RNase J2 in these species.
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- Environmental Biology
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Ecology and genomic features of infection with Mycobacterium avium subspecies paratuberculosis in Egypt
Mycobacterium avium subspecies paratuberculosis (M. paratuberculosis) is the causative agent of paratuberculosis, or Johne’s disease, in cattle, with potential involvement in cases of Crohn’s disease in humans. Johne’s disease is found worldwide and is economically important for both beef and dairy industries. In an effort to characterize this important infection in Egypt, we analysed the ecological and genomic features of recent isolates of M. paratuberculosis. In this report, we examined 26 Holstein dairy herds distributed throughout Egypt, from 2010 to 2013. Using PCR analysis of faecal samples, we estimated a mean herd-level prevalence of 65.4 %, with animal-level infection that reached a mean of 13.6 % among animals suffering from diarrhoea. Whole genome sequencing of field isolates identified numerous single nucleotide polymorphisms among field isolates relative to the standard M. paratuberculosis K10 genome. Interestingly, the virulence of M. paratuberculosis isolates from Egypt revealed diverse virulence phenotypes in the murine model of paratuberculosis, with significant differences in tissue colonization, particularly during the chronic stage of infection. Overall, our analysis confirmed that Johne’s disease is a newly identified problem in Egypt and indicated that M. paratuberculosis has potentially diverse genotypes that impact its virulence. Further ecological mapping and genomic analysis of M. paratuberculosis will enhance our understanding of the transmission and evolutionary dynamics of this pathogen under natural field conditions.
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- Environmental and Evolutionary Microbiology
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Microcystin-LR-induced cytotoxicity and apoptosis in human embryonic kidney and human kidney adenocarcinoma cell lines
Microcystin-LR (MC-LR) is a potent hepatotoxin, and increasing evidence suggests that it might also induce kidney injury. The aim of the present work was to evaluate the cytotoxicity and possible apoptotic effects of MC-LR on a human embryonic kidney cell line (HEK-293) and human kidney adenocarcinoma cell line (ACHN). Cells were exposed for 24 h to pure MC-LR (1.0–200 µM) and the cytotoxic effects were evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and sulphorhodamine B (SRB) cell viability assays. Cell viability in both cell lines was significantly decreased after treatment with MC-LR at 50 µM for 24 h (P<0.001). Moreover, MC-LR-treated ACHN and HEK-293 cells exhibited a marked dose-dependent loss of confluence as judged by phase-contrast microscopy. Similarly, fluorescence microscopic observations following acridine orange–ethidium bromide (AO/EB) staining confirmed that both cell types were undergoing apoptosis after treatment with MC-LR for 24 h. Expression of three apoptosis-related genes, Bax, Survivin and p53, was analysed by quantitative reverse transcriptase PCR analysis. Both Bax and p53 functioned as promoters of MC-LR-mediated apoptosis in ACHN and HEK-293 cells. The Survivin gene acted as a suppressor of apoptosis at lower MC-LR concentration (1 µM) and the gene was upregulated at higher MC-LR concentration (10 µM) (P<0.001). Significant increases of caspase 3 (P<0.0001) and caspase 9 (P<0.0001) activity were detected in both cell lines after exposure to MC-LR for 24 h, indicating the MC-LR induces cytotoxicity and a marked apoptosis in both ACHN and HEK-293 kidney cell lines.
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Heterotrophic nitrification and aerobic denitrification at low nutrient conditions by a newly isolated bacterium, Acinetobacter sp. SYF26
More LessA new strain, named SYF26, was isolated from the Hei He oligotrophic drinking-water reservoir in China. Based on its phenotypic and phylogenetic characteristics, the isolate was identified as a species of genus Acinetobacter. Strain SYF26 was able to grow at low NH4 +-N concentrations (5.46 mg l−1), and the nitrification rate was 0.064 mg NH4 +-N l−1 h−1. Low accumulation of nitrate and nitrite was observed throughout the ammonium removal experiment. Strain SYF26 reduced NO3 −-N or NO2 −-N. Nitrite reductase and periplasmic nitrate reductase were detectable. The putative nitrogen removal process carried out by the strain SYF26 is as follows: NH4 +→NH2OH→NO2 −→NO3 −, then NO3 −→NO2 −→N2. Response surface methodology analysis demonstrated that the maximum removal of ammonium occurred under the following conditions: NH4 +-N concentration of 22.05 mg l−1, C/N ratio of 4.31, initial pH of 7.78 and temperature of 29.73 °C, where initial pH and temperature had the largest influence on ammonium removal.
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- Microbial Pathogenicity
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Identification of a novel DNase of Streptococcus suis (EndAsuis) important for neutrophil extracellular trap degradation during exponential growth
The porcine and human pathogen Streptococcus suis induces and degrades neutrophil extracellular traps (NETs) in vitro. In this study, we investigated the working hypothesis that NET degradation is mediated not only by the known secreted S. suis nuclease A (SsnA) but also by a so-far undescribed putative endonuclease A of S. suis (designated EndAsuis) homologous to the pneumococcal endonuclease A (EndA). Comparative analysis was conducted to identify differences in localization, expression and function of EndAsuis and SsnA. In contrast to ssnA, endAsuis RNA expression was not substantially different during exponential and stationary growth. Modelling of the 3D structure confirmed a putative DRGH-motif-containing ββα-metal finger catalytic core in EndAsuis. Accordingly, nuclease activity of recombinant EndAsuis with a point-mutated H165 was rescued through imidazol treatment. In accordance with a putative membrane anchor, nuclease activity caused by endAsuis was not detectable in the supernatant. Importantly, endAsuis determined nuclease activity of S. suis prominently during exponential growth. This activity depended on the presence of Mg2+ but, in contrast to SsnA activity, not on Ca2+. A pH of 5.4 did not inhibit endAsuis-encoded nuclease activity during exponential growth. NET degradation of S. suis harvested during exponential growth was significantly attenuated in the endAsuis mutant. In contrast to SsnA, mutagenesis of endAsuis did not result in a significantly higher susceptibility against the antimicrobial effect mediated by NETs. As degradation of bacterial DNA caused by S. suis depended on ssnA and endAsuis, further functions of both factors in the host–pathogen interaction might be envisioned.
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Novel Leptospira interrogans protein Lsa32 is expressed during infection and binds laminin and plasminogen
Pathogenic Leptospira is the aetiological agent of leptospirosis, a life-threatening disease of human and veterinary concern. The quest for novel antigens that could mediate host–pathogen interactions is being pursued. Owing to their location, these antigens have the potential to elicit numerous activities, including immune response and adhesion. This study focuses on a hypothetical protein of Leptospira, encoded by the gene LIC11089, and its three derived fragments: the N-terminal, intermediate and C terminus regions. The gene coding for the full-length protein and fragments was cloned and expressed in Escherichia coli BL21(SI) strain by using the expression vector pAE. The recombinant protein and fragments tagged with hexahistidine at the N terminus were purified by metal affinity chromatography. The leptospiral full-length protein, named Lsa32 (leptospiral surface adhesin, 32 kDa), adheres to laminin, with the C terminus region being responsible for this interaction. Lsa32 binds to plasminogen in a dose-dependent fashion, generating plasmin when an activator is provided. Moreover, antibodies present in leptospirosis serum samples were able to recognize Lsa32. Lsa32 is most likely a new surface protein of Leptospira, as revealed by proteinase K susceptibility. Altogether, our data suggest that this multifaceted protein is expressed during infection and may play a role in host–L. interrogans interactions.
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Two specific amino acid variations in colonization factor CS6 subtypes of enterotoxigenic Escherichia coli results in differential binding and pathogenicity
CS6 is the predominant colonization factor of enterotoxigenic Escherichia coli (ETEC). We report the existence of multiple CS6 subtypes caused by natural point mutations in cssA and cssB, the structural genes for CS6. The subtype AIBI was mostly associated with ETEC isolated from diarrhoeal cases, whereas AIIBII was mostly found in asymptomatic controls. Here we explore the rationale behind this association. ETEC isolates expressing AIIBII showed weaker adherence to intestinal epithelial cells compared with ETEC expressing AIBI. AIIBII expression on the ETEC cell surface was threefold less than AIBI. We found that alanine at position 37 in CssAII, in conjunction with asparagine at position 97 in CssBII, was responsible for the decreased levels of AIIBII on the bacterial surface. In addition, purified AIIBII showed fourfold less mucin binding compared with AIBI. The asparagine at position 97 in CssBII was also accountable for the decreased mucin binding by AIIBII. Reduced fluid accumulation and colonization occurred during infection with ETEC expressing AIIBII in animal models. Together these results indicate that the differential adherence between AIBI and AIIBII was a cumulative effect of decreased surface-level expression and mucin binding of AIIBII due to two specific amino acid variations. As a consequence, ETEC expressing these two subtypes displayed differential pathogenicity. We speculate that this might explain the subjective association of AIBI with ETEC from diarrhoeal cases and AIIBII with asymptomatic controls.
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- Physiology and Biochemistry
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FUBT, a putative MFS transporter, promotes secretion of fusaric acid in the cotton pathogen Fusarium oxysporum f. sp. vasinfectum
Fusaric acid (FA) is a key component in virulence and symptom development in cotton during infection by Fusarium oxysporum. A putative major facilitator superfamily (MFS) transporter gene was identified downstream of the polyketide synthase gene responsible for the biosynthesis of FA in a region previously believed to be unrelated to the known FA gene cluster. Disruption of the transporter gene, designated FUBT, resulted in loss of FA secretion, decrease in FA production and a decrease in resistance to high concentrations of FA. Uptake of exogenous FA was unaffected in the disruption transformants, suggesting that FA enters the cell in Fusarium by an independent mechanism. Thus, FUBT is involved both in the extracellular transport of FA and in resistance of F. oxysporum to this non-specific toxin. A potential secondary resistance mechanism, the production of FA derivatives, was observed in FUBT deletion mutants. Molecular analysis of key biochemical processes in the production of FA could lead to future host plant resistance to Fusarium pathogens.
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Degradation of SsrA-tagged proteins in streptococci
More LessIn prokaryotes, a conserved small RNA molecule, called tmRNA, rescues ribosomes from proteins that are abnormally truncated due to the presence of rare codons or degraded mRNA. During the rescue process, a peptide tag (SsrA) encoded by tmRNA is cotranslationally added to the truncated polypeptides, thereby targeting these proteins for proteolytic degradation. In Escherichia coli, ClpXP and ClpAP proteases primarily degrade SsrA-tagged proteins. Other proteases such as Lon and FtsH also participate in the degradation in E. coli. However, in Bacillus subtilis, ClpXP is the major protease that degrades the SsrA-tagged proteins. Degradation of SsrA-tagged protein in streptococci is not well understood except that ClpXP is responsible for the majority of the degradation. Here we show that in Streptococcus mutans, in addition to ClpXP, two other Clp complexes, ClpCP and ClpEP, are also involved in the degradation. We also found that ClpCP- and ClpEP-mediated proteolysis of SsrA-tagged substrates is induced by heat stress. As ClpCP and ClpEP proteins are highly conserved in streptococci, we predicted that ClpEP- and ClpCP-mediated degradation of SsrA-tagged proteins might be operational in other streptococci.
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Volume 50 (1968)
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Volume 49 (1967)
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Volume 48 (1967)
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Volume 47 (1967)
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Volume 46 (1967)
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Volume 45 (1966)
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Volume 44 (1966)
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Volume 43 (1966)
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Volume 42 (1966)
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Volume 41 (1965)
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Volume 40 (1965)
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Volume 39 (1965)
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Volume 38 (1965)
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Volume 37 (1964)
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Volume 36 (1964)
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Volume 35 (1964)
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Volume 34 (1964)
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Volume 33 (1963)
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Volume 32 (1963)
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Volume 31 (1963)
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Volume 30 (1963)
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Volume 29 (1962)
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Volume 28 (1962)
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Volume 27 (1962)
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Volume 26 (1961)
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Volume 25 (1961)
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Volume 24 (1961)
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Volume 23 (1960)
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Volume 22 (1960)
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Volume 21 (1959)
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Volume 20 (1959)
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Volume 19 (1958)
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Volume 18 (1958)
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Volume 17 (1957)
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Volume 16 (1957)
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Volume 15 (1956)
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Volume 14 (1956)
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Volume 13 (1955)
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Volume 12 (1955)
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Volume 11 (1954)
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Volume 10 (1954)
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Volume 9 (1953)
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Volume 8 (1953)
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Volume 7 (1952)
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Volume 6 (1952)
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Volume 5 (1951)
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Volume 4 (1950)
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Volume 3 (1949)
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Volume 2 (1948)
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Volume 1 (1947)