Differential gene expression in Escherichia coli during aerosolization from liquid suspension. - Related Documents




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616701.0000Differential gene expression in Escherichia coli during aerosolization from liquid suspension. Comparative transcriptome analysis was used to determine the differentially expressed genes in Escherichia coli during aerosolization from liquid suspension. Isogenic mutant studies were then used to examine the potential part played by some of these genes in bacterial survival in the air. Bioaerosols were sampled after 3 min of nebulization, which aerosolized the bacteria from the liquid suspension to an aerosol chamber (A0), and after further 30 min of airborne suspension in the chamber (A30). Bacteria at A0 showed 65 differentially expressed genes (30 downregulated and 35 upregulated) as compared to the original bacteria in the nebulizer. Droplet evaporation models predicted a drop in temperature in the bioaerosols, which coincides with the change in the expression of cold shock protein genes-cspB and cspG in the bacteria. The most notable group of differentially expressed genes was sorbitol transport and metabolism genes (srlABDEMR). Other genes associated with osmotic stress, nutrient limitation, DNA damage, and other stresses were differentially expressed in the bacteria at A0. After further airborne suspension, one gene (ypfM, which encodes a hypothetical protein with unknown function) was downregulated in the bacteria at A30 as compared to those at A0. Finally, isogenic mutants with either the dps or srlA gene deleted (both genes were upregulated at A0) had lower survival than the parental strain, which is a sign of their potential ability to protect the bacteria in the air.201829808326
617210.9990Resistance and susceptibility of mice to bacterial infection. IV. Genetic and cellular basis of resistance to chronic infection with Brucella abortus. The number of Brucella abortus strain 19 organisms in the spleens of CBA/H mice peaked two weeks after intravenous injection of 5 X 10(6) organisms. With the onset of specific cell-mediated immunity, 90% of the bacteria were killed, but approximately 10(6) bacteria persisted up to seven weeks after infection. In contrast, in BALB/c, C57BL/10, and B10Br mice, bacterial numbers peaked at two weeks but decreased steadily with the onset of bactericidal activity. In all strains, clearance of bacteria from the liver was relatively efficient. The course of infection in (CBA/H X BALB/c) F1 mice was similar to that in CBA/H mice, indicating that the mechanism(s) leading to slower recovery from infection was dominant. The H-2 haplotype of the mice did not influence the rate of recovery from infection. The use of backcross mice showed that multiple genes were involved. In bone marrow-chimeric mice, resistance was determined by the genome of the bone marrow donor, not that of the host.19826809847
617020.9988Resistance and susceptibility of mice to bacterial infection. IV. Functional specificity in natural resistance to facultative intracellular bacteria. The effect of opsonic antibody on resistance of susceptibility of three strains of mice, C57Bl/10, BALB/c, and CBA to the intracellular bacteria Listeria monocytogenes, Salmonella typhimurium, and Brucella abortus was tested. Bacteria were opsonized by serum treatment before their injection into mice, or the mice were preimmunized by injection with alcohol killed bacteria which induces antibody without macrophage activation. Antibody did not increase the rate of clearance of Listeria from the bloodstream, nor did it affect the subsequent growth of that organism in the spleen and liver. Blood clearance of S. typhimurium and of B. abortus was increased by preopsonization with specific antibody, indicating that opsonins were a limiting factor in resistance to these two bacteria. However, neither opsonization before infection nor immunization with alcohol killed vaccines had any effect on the strain distribution of resistance/susceptibility, which differs for each of the three intracellular pathogens. Thus, even in the presence of adequate opsonization the three strains of mice showed different patterns of resistance/susceptibility to Listeria, S. typhimurium, and B. abortus. This implies that each has a unique cellular mechanism of early nonspecific resistance.19836413682
18730.9987Functional coexistence of twin arsenic resistance systems in Pseudomonas putida KT2440. The genome of the soil bacterium Pseudomonas putida KT2440 bears two virtually identical arsRBCH operons putatively encoding resistance to inorganic arsenic species. Single and double chromosomal deletions in each of these ars clusters of this bacterium were tested for arsenic sensitivity and found that the contribution of each operon to the resistance to the metalloid was not additive, as either cluster sufficed to endow cells with high-level resistance. However, otherwise identical traits linked to each of the ars sites diverged when temperature was decreased. Growth of the various mutants at 15°C (instead of the standard 30°C for P. putida) uncovered that ars2 affords a much higher resistance to As (III) than the ars1 counterpart. Reverse transcription polymerase chain reaction of arsB1 and arsB2 genes as well as lacZ fusions to the Pars1 and Pars2 promoters traced the difference to variations in transcription of the corresponding gene sets at each temperature. Functional redundancy may thus be selected as a stable condition - rather than just as transient state - if it affords one key activity to be expressed under a wider range of physicochemical settings. This seems to provide a straightforward solution to regulatory problems in environmental bacteria that thrive under changing scenarios.201524673935
621940.9987Isolation and characterization of bacteriophage-resistant mutants of Vibrio cholerae O139. Vibrio cholerae O139 strains produce a capsule which is associated with complement resistance and is used as a receptor by bacteriophage JA1. Spontaneous JA1-resistant mutants were found to have several phenotypes, with loss of capsule and/or O-antigen from the cell surface. Determination of the residual complement resistance and infant mouse colonization potential of each mutant suggested that production of O-antigen is of much greater significance than the presence of capsular material for both of these properties. Two different in vitro assays of complement resistance were compared and the results of one shown to closely reflect the comparative recoveries of bacteria from the colonization experiments. Preliminary complementation studies implicated two rfb region genes, wzz and wbfP, as being essential for the biosynthesis of capsule but not O-antigen.200111312617
629250.9987Genome-Wide Screening and Characterization of Genes Involved in Response to High Dose of Ciprofloxacin in Escherichia coli. The global emergence of antibiotic resistance, especially in Gram-negative bacteria, is an urgent threat to public health. Inevitably, considering its extensive use and misuse, resistance toward ciprofloxacin has increased in almost all clinically relevant bacteria. This study aimed to investigate the transcriptome changes at a high concentration of ciprofloxacin in Escherichia coli. In brief, 1,418 differentially expressed genes (DEGs) were identified, from which 773 genes were upregulated by ciprofloxacin, whereas 651 genes were downregulated. Enriched biological pathways reflected the upregulation of biological processes such as DNA damage and repair system, toxin/antitoxin systems, formaldehyde detoxification system. With kyoto encyclopedia of genes and genomes pathway analysis, higher expressed DEGs were associated with "LPS biosynthesis," "streptomycin biosynthesis," and "polyketide sugar unit biosynthesis." Lower expressed DEGs were associated with "biosynthesis of amino acids" and "flagellar assembly" pathways. After treatment of ciprofloxacin, lipopolysaccharide (LPS) release was increased by two times, and the gene expression level of LPS synthesis was elevated (p < 0.05) in both reference and clinical strains. Our results demonstrated that transient exposure to high-dose ciprofloxacin is a double-edged sword. Cautions should be taken when administering high-dose antibiotic treatment for infectious diseases.202235512736
823060.9987Functional characterization and biological significance of Yersinia pestis lipopolysaccharide biosynthesis genes. In silico analysis of available bacterial genomes revealed the phylogenetic proximity levels of enzymes responsible for biosynthesis of lipopolysaccharide (LPS) of Yersinia pestis, the cause of plague, to homologous proteins of closely related Yersinia spp. and some other bacteria (Serratia proteamaculans, Erwinia carotovora, Burkholderia dolosa, Photorhabdus luminescens and others). Isogenic Y. pestis mutants with single or double mutations in 14 genes of LPS biosynthetic pathways were constructed by site-directed mutagenesis on the base of the virulent strain 231 and its attenuated derivative. Using high-resolution electrospray ionization mass spectrometry, the full LPS structures were elucidated in each mutant, and the sequence of monosaccharide transfers in the assembly of the LPS core was inferred. Truncation of the core decreased significantly the resistance of bacteria to normal human serum and polymyxin B, the latter probably as a result of a less efficient incorporation of 4-amino-4-deoxyarabinose into lipid A. Impairing of LPS biosynthesis resulted also in reduction of LPS-dependent enzymatic activities of plasminogen activator and elevation of LD(50) and average survival time in mice and guinea pigs infected with experimental plague. Unraveling correlations between biological properties of bacteria and particular LPS structures may help a better understanding of pathogenesis of plague and implication of appropriate genes as potential molecular targets for treatment of plague.201121999543
830470.9986A Shift to Human Body Temperature (37°C) Rapidly Reprograms Multiple Adaptive Responses in Escherichia coli That Would Facilitate Niche Survival and Colonization. One of the first environmental cues sensed by a microbe as it enters a human host is an upshift in temperature to 37°C. In this dynamic time point analysis, we demonstrate that this environmental transition rapidly signals a multitude of gene expression changes in Escherichia coli. Bacteria grown at 23°C under aerobic conditions were shifted to 37°C, and mRNA expression was measured at time points after the shift to 37°C (t = 0.5, 1, and 4 h). The first hour is characterized by a transient shift to anaerobic respiration strategies and stress responses, particularly acid resistance, indicating that temperature serves as a sentinel cue to predict and prepare for various niches within the host. The temperature effects on a subset of stress response genes were shown to be mediated by RpoS and directly correlated with RpoS, DsrA, and RprA levels, and increased acid resistance was observed that was dependent on 23°C growth and RpoS. By 4 h, gene expression shifted to aerobic respiration pathways and decreased stress responses, coupled with increases in genes associated with biosynthesis (amino acid and nucleotides), iron uptake, and host defense. ompT, a gene that confers resistance to antimicrobial peptides, was highly thermoregulated, with a pattern conserved in enteropathogenic and uropathogenic E. coli strains. An immediate decrease in curli gene expression concomitant with an increase in flagellar gene expression implicates temperature in this developmental decision. Together, our studies demonstrate that temperature signals a reprogramming of gene expression immediately upon an upshift that may predict, prepare, and benefit the survival of the bacterium within the host. IMPORTANCE As one of the first cues sensed by the microbe upon entry into a human host, understanding how bacteria like E. coli modulate gene expression in response to temperature improves our understanding of how bacteria immediately initiate responses beneficial for survival and colonization. For pathogens, understanding the various pathways of thermal regulation could yield valuable targets for anti-infective chemotherapeutic drugs or disinfection measures. In addition, our data provide a dynamic examination of the RpoS stress response, providing genome-wide support for how temperature impacts RpoS through changes in RpoS stability and modulation by small regulatory RNAs.202134516284
617180.9986Host response to infection with a temperature-sensitive mutant of Salmonella typhimurium in a susceptible and a resistant strain of mice. The inoculation of a temperature-sensitive mutant of Salmonella typhimurium induced a long-lasting infection in susceptible (C57BL/6) and resistant (A/J) mice. During week 1 of infection, the number of bacteria in the spleens was similar in both mouse strains. Then, the decrease of bacteria was more rapid in the resistant strain. Splenomegaly and granulomatous hepatitis were more severe in the susceptible strain. The immune response induced by this infection was studied. In both mouse strains delayed-type hypersensitivity to Salmonella antigens was present, and resistance to reinfection with a virulent strain of S. typhimurium or with Listeria monocytogenes appeared with the same kinetics. Thus, it does not seem that the gene(s) controlling natural resistance to S. typhimurium act(s) on acquired immunity.19853897053
69390.9986Effect of acid adaptation on the fate of Listeria monocytogenes in THP-1 human macrophages activated by gamma interferon. In Listeria monocytogenes the acid tolerance response (ATR) takes place through a programmed molecular response which ensures cell survival under unfavorable conditions. Much evidence links ATR with virulence, but the molecular determinants involved in the reactivity to low pHs and the behavior of acid-exposed bacteria within host cells are still poorly understood. We have investigated the effect of acid adaptation on the fate of L. monocytogenes in human macrophages. Expression of genes encoding determinants for cell invasion and intracellular survival was tested for acid-exposed bacteria, and invasive behavior in the human myelomonocytic cell line THP-1 activated with gamma interferon was assessed. Functional approaches demonstrated that preexposure to an acidic pH enhances the survival of L. monocytogenes in activated human macrophages and that this effect is associated with an altered pattern of expression of genes involved in acid resistance and cell invasion. Significantly decreased transcription of the plcA gene, encoding a phospholipase C involved in vacuolar escape and cell-to-cell spread, was observed in acid-adapted bacteria. This effect was due to a reduction in the quantity of the bicistronic plcA-prfA transcript, concomitant with an increase in the level(s) of the monocistronic prfA mRNA(s). The transcriptional shift from distal to proximal prfA promoters resulted in equal levels of the prfA transcript (and, as a consequence, of the inlA, hly, and actA transcripts) under neutral and acidic conditions. In contrast, the sodC and gad genes, encoding a cytoplasmic superoxide dismutase and the glutamate-based acid resistance system, respectively, were positively regulated at a low pH. Morphological approaches confirmed the increased intracellular survival and growth of acid-adapted L. monocytogenes cells both in vacuoles and in the cytoplasm of interferon gamma-activated THP-1 macrophages. Our data indicate that preexposure to a low pH has a positive impact on subsequent challenge of L. monocytogenes with macrophagic cells.200212117947
8882100.9986Transcriptome Profiling of Wild-Type and pga-Knockout Mutant Strains Reveal the Role of Exopolysaccharide in Aggregatibacter actinomycetemcomitans. Exopolysaccharides have a diverse set of functions in most bacteria including a mechanistic role in protecting bacteria against environmental stresses. Among the many functions attributed to the exopolysaccharides, biofilm formation, antibiotic resistance, immune evasion and colonization have been studied most extensively. The exopolysaccharide produced by many Gram positive as well as Gram negative bacteria including the oral pathogen Aggregatibacter actinomycetemcomitans is the homopolymer of β(1,6)-linked N-acetylglucosamine. Recently, we reported that the PGA-deficient mutant of A. actinomycetemcomitans failed to colonize or induce bone resorption in a rat model of periodontal disease, and the colonization genes, apiA and aae, were significantly down regulated in the mutant strain. To understand the role of exopolysaccharide and the pga locus in the global expression of A. actinomycetemcomitans, we have used comparative transcriptome profiling to identify differentially expressed genes in the wild-type strain in relation to the PGA-deficient strain. Transcriptome analysis revealed that about 50% of the genes are differently expressed (P < 0.05 and fold change >1.5). Our study demonstrated that the absence of the pga locus affects the genes involved in peptidoglycan recycling, glycogen storage, and virulence. Further, using confocal microscopy and plating assays, we show that the viability of pga mutant strain is significantly reduced during biofilm growth. Thus, this study highlights the importance of pga genes and the exopolysaccharide in the virulence of A. actinomycetemcomitans.201526221956
6169110.9986The effect of mating on immunity can be masked by experimental piercing in female Drosophila melanogaster. Mating and immunity are two major components of fitness and links between them have been demonstrated in a number of recent investigations. In Drosophila melanogaster, a seminal fluid protein, sex-peptide (SP), up-regulates a number of antimicrobial peptide (AMP) genes in females after mating but the resulting effect on pathogen resistance is unclear. In this study, we tested (1) whether SP-induced changes in gene expression affect the ability of females to kill injected non-pathogenic bacteria and (2) how the injection process per se affects the expression of AMP genes relative to SP. The ability of virgin females and females mated to SP lacking or control males to clear bacteria was assayed using an established technique in which Escherichia coli are injected directly into the fly body and the rate of clearance of the injected bacteria is determined. We found no repeatable differences in clearance rates between virgin females and females mated to SP producing or SP lacking males. However, we found that the piercing of the integument, as occurs during injection, up-regulates AMP gene expression much more strongly than SP. Thus, assays that involve piercing, which are commonly used in immunity studies, can mask more subtle and biologically relevant changes in immunity, such as those induced by mating.200818068720
8228120.9986Brucella abortus genes identified following constitutive growth and macrophage infection. The chronicity of Brucella abortus infection in humans and animals depends on the organism's ability to escape host defenses by gaining entry and surviving inside the macrophage. Although no human vaccine exists for Brucella, vaccine development in other bacteria has been based on deletions of selective nutritional as well as regulatory systems. Our goal is to develop a vaccine for Brucella. To further this aim, we have used a green fluorescent protein (GFP) reporter system to identify constitutively and intracellularly induced B. abortus genes. Constitutively producing gfp clones exhibited sequence homology with genes associated with protein synthesis and metabolism (initiation factor-1 and tRNA ribotransferase) and detoxification (organic hydroperoxidase resistance). Of greater interest, clones negative for constitutively produced gfp in agar were examined by fluorescence microscopy to detect promoter activity induced within macrophages 4 and 24 h following infection. Bacterial genes activated in macrophages 4 h postinfection appear to be involved in adapting to intracellular environmental conditions. Included in this group were genes for detoxification (lactoglyglutathione lyase gene), repair (formamidopyrimidine-DNA glycosylase gene), osmotic protection (K(+) transport gene), and site-specific recombination (xerD gene). A gene involved in metabolism and biosynthesis (deoxyxylulose 5' phosphate synthase gene) was also identified. Genes activated 24 h following infection were biosynthesis- and metabolism-associated genes (iron binding protein and rhizopine catabolism). Identification of B. abortus genes that are activated following macrophage invasion provides insight into Brucella pathogenesis and thus is valuable in vaccine design utilizing selective targeted deletions of newly identified Brucella genes.200111705955
6339130.9986Novel acid resistance genes from the metagenome of the Tinto River, an extremely acidic environment. Microorganisms that thrive in acidic environments are endowed with specialized molecular mechanisms to survive under this extremely harsh condition. In this work, we performed functional screening of six metagenomic libraries from planktonic and rhizosphere microbial communities of the Tinto River, an extremely acidic environment, to identify genes involved in acid resistance. This approach has revealed 15 different genes conferring acid resistance to Escherichia coli, most of which encoding putative proteins of unknown function or previously described proteins not known to be related to acid resistance. Moreover, we were able to assign function to one unknown and three hypothetical proteins. Among the recovered genes were the ClpXP protease, the transcriptional repressor LexA and nucleic acid-binding proteins such as an RNA-binding protein, HU and Dps. Furthermore, nine of the retrieved genes were cloned and expressed in Pseudomonas putida and Bacillus subtilis and, remarkably, most of them were able to expand the capability of these bacteria to survive under severe acid stress. From this set of genes, four presented a broad-host range as they enhance the acid resistance of the three different organisms tested. These results expand our knowledge about the different strategies used by microorganisms to survive under extremely acid conditions.201323145860
682140.9986Comparative transcriptome analysis of Brucella melitensis in an acidic environment: Identification of the two-component response regulator involved in the acid resistance and virulence of Brucella. Brucella melitensis, encounters a very stressful environment in phagosomes, especially low pH levels. So identifying the genes that contribute to the replication and survival within an acidic environment is critical in understanding the pathogenesis of the Brucella bacteria. In our research, comparative transcriptome with RNA-seq were used to analyze the changes of genes in normal-medium culture and in pH4.4-medium culture. The results reveal that 113 genes expressed with significant differences (|log2Ratio| ≥ 3); about 44% genes expressed as up-regulated. With GO term analysis, structural constituent of the ribosome, rRNA binding, structural molecule activity, and cation-transporting ATPase activity were significantly enriched (p-value ≤ 0.05). These genes distributed in 51 pathways, in which ribosome and photosynthesis pathways were significantly enriched. Six pathways (oxidative phosphorylation, iron-transporting, bacterial secretion system, transcriptional regulation, two-component system, and ABC transporters pathways) tightly related to the intracellular survival and virulence of Brucella were analyzed. A two-component response regulator gene in the transcriptional regulation pathway, identified through gene deletion and complementary technologies, played an important role in the resistance to the acid-resistance and virulence of Brucella.201626691825
6294150.9986Comparison of Gene Expression Profiles of Uropathogenic Escherichia Coli CFT073 after Prolonged Exposure to Subinhibitory Concentrations of Different Biocides. Biocides are chemical compounds widely used for sterilization and disinfection. The aim of this study was to examine whether exposure to subinhibitory biocide concentrations influenced transcriptional expression of genes that could improve a pathogen's drug resistance or fitness. We used DNA microarrays to investigate the transcriptome of the uropathogenic Escherichia coli strain CFT073 in response to prolonged exposure to subinhibitory concentrations of four biocides: benzalkonium chloride, chlorhexidine, hydrogen peroxide and triclosan. Transcription of a gene involved in polymyxin resistance, arnT, was increased after treatment with benzalkonium chloride. However, pretreatment of the bacteria with this biocide did not result in cross-resistance to polymyxin in vitro. Genes encoding products related to transport formed the functional group that was most affected by biocides, as 110 out of 884 genes in this category displayed altered transcription. Transcripts of genes involved in cysteine uptake, sulfate assimilation, dipeptide transport, as well as cryptic phage genes were also more abundant in response to several biocides. Additionally, we identified groups of genes with transcription changes unique to single biocides that might include potential targets for the biocides. The biocides did not increase the resistance potential of the pathogen to other antimicrobials.201931569631
6168160.9986SdiA aids enterohemorrhagic Escherichia coli carriage by cattle fed a forage or grain diet. Enterohemorrhagic Escherichia coli (EHEC) causes hemorrhagic colitis and life-threatening complications. The main reservoirs for EHEC are healthy ruminants. We reported that SdiA senses acyl homoserine lactones (AHLs) in the bovine rumen to activate expression of the glutamate acid resistance (gad) genes priming EHEC's acid resistance before they pass into the acidic abomasum. Conversely, SdiA represses expression of the locus of enterocyte effacement (LEE) genes, whose expression is not required for bacterial survival in the rumen but is necessary for efficient colonization at the rectoanal junction (RAJ) mucosa. Our previous studies show that SdiA-dependent regulation was necessary for efficient EHEC colonization of cattle fed a grain diet. Here, we compared the SdiA role in EHEC colonization of cattle fed a forage hay diet. We detected AHLs in the rumen of cattle fed a hay diet, and these AHLs activated gad gene expression in an SdiA-dependent manner. The rumen fluid and fecal samples from hay-fed cattle were near neutrality, while the same digesta samples from grain-fed animals were acidic. Cattle fed either grain or hay and challenged with EHEC orally carried the bacteria similarly. EHEC was cleared from the rumen within days and from the RAJ mucosa after approximately one month. In competition trials, where animals were challenged with both wild-type and SdiA deletion mutant bacteria, diet did not affect the outcome that the wild-type strain was better able to persist and colonize. However, the wild-type strain had a greater advantage over the SdiA deletion mutant at the RAJ mucosa among cattle fed the grain diet.201323836826
158170.9986Homology- and cross-resistance of Lactobacillus plantarum to acid and osmotic stress and the influence of induction conditions on its proliferation by RNA-Seq. In this study, homology- and cross-resistance of Lactobacillus plantarum L1 and Lactobacillus plantarum L2 to acid and osmotic stress were investigated. Meanwhile, its proliferation mechanism was demonstrated by transcriptomic analysis using RNA sequencing. We found that the homologous-resistance and cross-resistance of L. plantarum L1 and L. plantarum L2 increased after acid and osmotic induction treatment by lactic acid and sodium lactate solution in advance, and the survival rate of live bacteria was improved. In addition, the count of viable bacteria of L. plantarum L2 significantly increased cultivated at a pH 5.0 with a 15% sodium lactate sublethal treatment, compared with the control group. Further study revealed that genes related to membrane transport, amino acid metabolism, nucleotide metabolism, and cell growth were significantly upregulated. These findings will contribute to promote high-density cell culture of starter cultures production in the fermented food industry.202133945164
6338180.9986Transcriptome Analysis of the Intracellular Facultative Pathogen Piscirickettsia salmonis: Expression of Putative Groups of Genes Associated with Virulence and Iron Metabolism. The intracellular facultative bacteria Piscirickettsia salmonis is one of the most important pathogens of the Chilean aquaculture. However, there is a lack of information regarding the whole genomic transcriptional response according to different extracellular environments. We used next generation sequencing (NGS) of RNA (RNA-seq) to study the whole transcriptome of an isolate of P. salmonis (FAVET-INBIOGEN) using a cell line culture and a modified cell-free liquid medium, with or without iron supplementation. This was done in order to obtain information about the factors there are involved in virulence and iron acquisition. First, the isolate was grown in the Sf21 cell line; then, the bacteria were cultured into a cell-free liquid medium supplemented or not with iron. We identified in the transcriptome, genes associated with type IV secretion systems, genes related to flagellar structure assembly, several proteases and sigma factors, and genes related to the development of drug resistance. Additionally, we identified for the first time several iron-metabolism associated genes including at least two iron uptake pathways (ferrous iron and ferric iron uptake) that are actually expressed in the different conditions analyzed. We further describe putative genes that are related with the use and storage of iron in the bacteria, which have not been previously described. Several sets of genes related to virulence were expressed in both the cell line and cell-free culture media (for example those related to flagellar structure; such as basal body, MS-ring, C-ring, proximal and distal rod, and filament), which may play roles in other basic processes rather than been restricted to virulence.201628033422
690190.9986Characterization of oxidative stress-resistant mutants of Streptococcus thermophilus CNRZ368. During industrial processes, the dairy organism Streptococcus thermophilus is exposed to stress conditions. Its ability to survive and grow in an aerobic environment indicates that it must possess defensive mechanisms against reactive oxygen species. To identify the genes involved in oxidative stress defence, a collection of mutants was generated by random insertional mutagenesis and screened for menadione sensitivity and resistance. Results obtained for resistant clones allowed the identification of eight loci. The insertions affected genes whose homologues in other bacteria were previously identified as being involved in stress response(deoB, gst) or transcription regulation (rggC) and five ORFs of unknown function. The tolerance of the eight mutants to air-exposure, methyl viologen and H2O2 was studied. Real-time quantitative PCR was used to analyse the transcript level of mutated genes and revealed that most were down-regulated during oxidative stress.200415378231