Detection of sialoglycomolecules in five plant trypanosomatids and in an insect phytophagous isolate

A mutation in the cell division gene ftsK causes super-induction of sigma(70)-dependent stress defense genes, such as uspA, during entry of cells into stationary phase. In contrast, we report here that stationary phase induction of sigma(S)-dependent genes, uspB and cfa, is attenuated and that sigma(S) accumulates at a lower rate in ftsK1 cells. Ectopic overexpression of rpoS restored induction of the rpoS regulon in the ftsK mutant, as did a deletion in the recA gene. Thus, a mutation in the cell division gene, ftsK, uncouples the otherwise coordinated induction of sigma(S)-dependent genes and the universal stress response gene, uspA, during entry into stationary phase.     

MiR-34a inhibits lymphatic metastasis potential of mouse hepatoma cells

Genetic adaptation is one of the key features of Escherichia coli (E. coli) that ensure its survival in different hostile environments. E. coli seems to initiate biofilm development in response to specific environmental cues. A number of properties inherent within bacterial biofilms indicate that their gene expression is different from that of planktonic bacteria. Two of the possible important genes are rpoS and bolA. The rpoS gene has been known as the alternative sigma (σ) factor, which controls the expression of a large number of genes, which are involved in responses to a varied number of stresses, as well as transition to stationary phase from exponential form of growth. Morphogene bolA response to stress environment leads to round morphology of E. coli cells, but little is known about its involvement in biofilms and its development or maintenance. The purpose of this study was to understand and analyse the responses of rpoS and bolA gene to sudden change in the environment. In this study, E. coli K-12 MG1655, rpoS, and bolA mutant strains were used and gene expression was studied. Results show that both genes contribute to the ability to respond and adapt in response to various types of stresses. RpoS response to various stress environments was somehow constant in both the planktonic and biofilm phases, whereas bolA responded well under various stress conditions, in both planktonic and biofilm mode, up to 5-6-fold change in the expression was noticed in the case of pH variation and hydrogen peroxide stress (H(2)O(2)) as compared with rpoS.     

Effect of rpoS gene knockout on the metabolism of Escherichia coli during exponential growth phase and early stationary phase based on gene expressions, enzyme activities and intracellular metabolite concentrations

The RNA polymerase sigma factor, encoded by rpoS gene, controls the expression of a large number of genes in Escherichia coli under stress conditions. The present study investigated the growth characteristics and metabolic pathways of rpoS gene knockout mutant of E. coli growing in LB media under aerobic condition. The analyses were made based on gene expressions obtained by DNA microarray and RT-PCR, enzyme activities and intracellular metabolite concentrations at the exponential and early stationary phases of growth. Although the glucose utilization pattern of the mutant was similar to the parent strain, the mutant failed to utilize acetate throughout the cultivation period. Microarray data indicated that the expression levels of several important genes of acetate metabolism such as acs, aceAB, cysDEK, fadR, etc. were significantly altered in the absence of rpoS gene. Interestingly, there was an increased activity of TCA cycle during the exponential growth phase, which was gradually diminished at the onset of stationary phase. Moreover, rpoS mutation had profound effect on the expression of several other genes of E. coli metabolic pathways that were not described earlier. The changes in the gene expressions, enzyme activities and intracellular metabolite concentrations of the rpoS mutant are discussed in details with reference to the major metabolic pathways of E. coli.     

rpoS Mutations and Loss of General Stress Resistance in Escherichia coli Populations as a Consequence of Conflict between Competing Stress Responses

The general stress resistance of Escherichia coli is controlled by the RpoS sigma factor (phi(S)), but mutations in rpoS are surprisingly common in natural and laboratory populations. Evidence for the selective advantage of losing rpoS was obtained from experiments with nutrient-limited bacteria at different growth rates. Wild-type bacteria were rapidly displaced by rpoS mutants in both glucose- and nitrogen-limited chemostat populations. Nutrient limitation led to selection and sweeps of rpoS null mutations and loss of general stress resistance. The rate of takeover by rpoS mutants was most rapid (within 10 generations of culture) in slower-growing populations that initially express higher phi(S) levels. Competition for core RNA polymerase is the likeliest explanation for reduced expression from distinct promoters dependent on phi(70) and involved in the hunger response to nutrient limitation. Indeed, the mutation of rpoS led to significantly higher expression of genes contributing to the high-affinity glucose scavenging system required for the hunger response. Hence, rpoS polymorphism in E. coli populations may be viewed as the result of competition between the hunger response, which requires sigma factors other than phi(S) for expression, and the maintenance of the ability to withstand external stresses. The extent of external stress significantly influences the spread of rpoS mutations. When acid stress was simultaneously applied to glucose-limited cultures, both the phenotype and frequency of rpoS mutations were attenuated in line with the level of stress. The conflict between the hunger response and maintenance of stress resistance is a potential weakness in bacterial regulation.     

The Legionella pneumophila rpoS Gene Is Required for Growth within Acanthamoeba castellanii

To investigate regulatory networks in Legionella pneumophila, the gene encoding the homolog of the Escherichia coli stress and stationary-phase sigma factor RpoS was identified by complementation of an E. coli rpoS mutation. An open reading frame that is approximately 60% identical to the E. coli rpoS gene was identified. Western blot analysis showed that the level of L. pneumophila RpoS increased in stationary phase. An insertion mutation was constructed in the rpoS gene on the chromosome of L. pneumophila, and the ability of this mutant strain to survive various stress conditions was assayed and compared with results for the wild-type strain. Both the mutant and wild-type strains were more resistant to stress when in stationary phase than when in the logarithmic phase of growth. This finding indicates that L. pneumophila RpoS is not required for a stationary-phase-dependent resistance to stress. Although the mutant strain was able to kill HL-60- and THP-1-derived macrophages, it could not replicate within a protozoan host, Acanthamoeba castellanii. These data suggest that L. pneumophila possesses a growth phase-dependent resistance to stress that is independent of RpoS control and that RpoS likely regulates genes that enable it to survive in the environment within protozoa. Our data indicate that the role of rpoS in L. pneumophila is very different from what has previously been reported for E. coli rpoS.     

Growth phase-regulated expression of bolA and morphology of stationary-phase Escherichia coli cells are controlled by the novel sigma factor sigma S.

The novel sigma factor (sigma S) encoded by rpoS (katF) is required for induction of many growth phase-regulated genes and expression of a variety of stationary-phase phenotypes in Escherichia coli. Here we demonstrate that wild-type cells exhibit spherical morphology in stationary phase, whereas rpoS mutant cells remain rod shaped and are generally larger. Size reduction of E. coli cells along the growth curve is a continuous and at least biphasic process, the second phase of which is absent in rpoS-deficient cells and correlates with induction of the morphogene bolA in wild-type cells. Stationary-phase induction of bolA is dependent on sigma S. The "gearbox" a characteristic sequence motif present in the sigma S-dependent growth phase- and growth rate-regulated bolAp1 promoter, is not recognized by sigma S, since stationary-phase induction of the mcbA promoter, which also contains a gearbox, does not require sigma S, and other sigma S-controlled promoters do not contain gearboxes. However, good homology to the potential -35 and -10 consensus sequences for sigma S regulation is found in the bolAp1 promoter.     

RpoS-regulated genes of Escherichia coli identified by random lacZ fusion mutagenesis

RpoS is a conserved alternative sigma factor that regulates the expression of many stress response genes in Escherichia coli. The RpoS regulon is large but has not yet been completely characterized. In this study, we report the identification of over 100 RpoS-dependent fusions in a genetic screen based on the differential expression of an operon-lacZ fusion bank in rpoS mutant and wild-type backgrounds. Forty-eight independent gene fusions were identified, including several in well-characterized RpoS-regulated genes, such as osmY, katE, and otsA. Many of the other fusions mapped to genes of unknown function or to genes that were not previously known to be under RpoS control. Based on the homology to other known bacterial genes, some of the RpoS-regulated genes of unknown functions are likely important in nutrient scavenging.     

Regulation of rpoS gene expression in Pseudomonas: involvement of a TetR family regulator

The rpoS gene encodes the sigma factor which was identified in several gram-negative bacteria as a central regulator during stationary phase. rpoS gene regulation is known to respond to cell density, showing higher expression in stationary phase. For Pseudomonas aeruginosa, it has been demonstrated that the cell-density-dependent regulation response known as quorum sensing interacts with this regulatory response. Using the rpoS promoter of P. putida, we identified a genomic Tn5 insertion mutant of P. putida which showed a 90% decrease in rpoS promoter activity, resulting in less RpoS being present in a cell at stationary phase. Molecular analysis revealed that this mutant carried a Tn5 insertion in a gene, designated psrA (Pseudomonas sigma regulator), which codes for a protein (PsrA) of 26.3 kDa. PsrA contains a helix-turn-helix motif typical of DNA binding proteins and belongs to the TetR family of bacterial regulators. The homolog of the psrA gene was identified in P. aeruginosa; the protein showed 90% identity to PsrA of P. putida. A psrA::Tn5 insertion mutant of P. aeruginosa was constructed. In both Pseudomonas species, psrA was genetically linked to the SOS lexA repressor gene. Similar to what was observed for P. putida, a psrA null mutant of P. aeruginosa also showed a 90% reduction in rpoS promoter activity; both mutants could be complemented for rpoS promoter activity when the psrA gene was provided in trans. psrA mutants of both Pseudomonas species lost the ability to induce rpoS expression at stationary phase, but they retained the ability to produce quorum-sensing autoinducer molecules. PsrA was demonstrated to negatively regulate psrA gene expression in Pseudomonas and in Escherichia coli as well as to be capable of activating the rpoS promoter in E. coli. Our data suggest that PsrA is an important regulatory protein of Pseudomonas spp. involved in the regulatory cascade controlling rpoS gene regulation in response to cell density.     

Induction of the Escherichia coli aidB gene under oxygen-limiting conditions requires a functional rpoS (katF) gene.

The Escherichia coli aidB gene is regulated by two different mechanisms, an ada-dependent pathway triggered by methyl damage to DNA and an ada-independent pathway triggered when cells are grown without aeration. In this report we describe our search for mutations affecting the ada-independent aidB induction pathway. The mutant strain identified carries two mutations affecting aidB expression. These mutations are named abrB (aidB regulator) and abrD. The abrB mutation is presently poorly characterized because of instability of the phenotype it imparts. The second mutation, abrD1, reduces the expression of aidB observed when aeration is ceased and oxygen becomes limiting. Genetic and phenotypic analysis of the abrD1 mutation demonstrates that it is an allele of rpoS. Thus, aidB is a member of the family of genes that are transcribed by a sigma S-directed RNA polymerase holoenzyme. Examination of aidB expression in an rpoS insertion mutant strain indicates that both rpoS13::Tn10 and abrD1 mutations reduce aidB expression under oxygen-limiting conditions that prevail in unaerated cultures, reduce aidB induction by acetate at a low pH, but have little or no effect on the ada-dependent alkylation induction of aidB.