Clostridioides difficile exploits toxin-mediated inflammation to alter the host nutritional landscape and exclude competitors from the gut microbiota.

Clostridioides difficile is a bacterial pathogen that causes a range of clinical disease from mild to moderate diarrhea, pseudomembranous colitis, and toxic megacolon. Typically, C. difficile infections (CDIs) occur after antibiotic treatment, which alters the gut microbiota, decreasing colonization resistance against C. difficile. Disease is mediated by two large toxins and the expression of their genes is induced upon nutrient depletion via the alternative sigma factor TcdR. Here, we use tcdR mutants in two strains of C. difficile and omics to investigate how toxin-induced inflammation alters C. difficile metabolism, tissue gene expression and the gut microbiota, and to determine how inflammation by the host may be beneficial to C. difficile. We show that C. difficile metabolism is significantly different in the face of inflammation, with changes in many carbohydrate and amino acid uptake and utilization pathways. Host gene expression signatures suggest that degradation of collagen and other components of the extracellular matrix by matrix metalloproteinases is a major source of peptides and amino acids that supports C. difficile growth in vivo. Lastly, the inflammation induced by C. difficile toxin activity alters the gut microbiota, excluding members from the genus Bacteroides that are able to utilize the same essential nutrients released from collagen degradation.

Immunogenicity and protective ability of RpoE against Streptococcus suis serotype 2.

AIMS: RpoE is quite immunogenic and can be used as a candidate vaccine for Streptococcus suis infection via immunoproteomics as reported in our previous studies. In this study, we aimed to verify the immunogenicity of recombinant RpoE and its protective effect against of S. suis. METHODS AND RESULTS: The RpoE protein was successfully expressed in Escherichia coli, and the purified recombinant protein was mixed with ISA206 to prepare an S. suis subunit vaccine. Mice were immunized with the RpoE subunit vaccine and then infected with the virulent S. suis strain ZY05719. Subunit vaccine-immunized mice achieved 50% protection, less pathological damage and less bacterial distribution in each organ compared with the control mice. Furthermore, in vitro culture, showed that mouse antisera significantly (P ï¼œ 0·001) inhibited the growth of S. suis, and qRT-PCR results showed that RpoE successfully induced the up-regulation of IL-6 and TNF-α cytokines. CONCLUSIONS: RpoE mice were vaccinated to obtain immune protection, which may be candidates for S. suis subunit vaccine. SIGNIFICANCE AND IMPACT OF THE STUDY: The results of this study will provide new ideas for the development of safe and effective recombinant subunits vaccines for S. suis.

Pleiotropic anti-anti-sigma factor BldG is phosphorylated by several anti-sigma factor kinases in the process of activating multiple sigma factors in Streptomyces coelicolor A3(2).

The anti-anti-sigma factor BldG has a pleiotropic function in Streptomyces coelicolor A3(2), regulating both morphological and physiological differentiation. Together with the anti-sigma factor UshX, it participates in a partner-switching activation of the sigma factor σH, which has a dual role in the osmotic stress response and morphological differentiation in S. coelicolor A3(2). In addition to UshX, BldG also interacts with the anti-sigma factor ApgA, although no target sigma factor has yet been identified. However, neither UshX nor ApgA phosphorylates BldG. This phosphorylation is provided by the anti-sigma factor RsfA, which is specific for the late developmental sigma factor σF. However, BldG is phosphorylated in the rsfA mutant, suggesting that some other anti-sigma factors containing HATPase_c kinase domain are capable to phosphorylate BldG in vivo. Bacterial two-hybrid system (BACTH) was therefore used to investigate the interactions of all suitable anti-sigma factors of S. coelicolor A3(2) with BldG. At least 15 anti-sigma factors were found to interact with BldG. These interactions were confirmed by native PAGE. In addition to RsfA, BldG is specifically phosphorylated on the conserved phosphorylation Ser57 residue by at least seven additional anti-sigma factors. However, only one of them, SCO7328, has been shown to interact with three sigma factors, σG, σK and σM. A mutant with deleted SCO7328 gene was prepared in S. coelicolor A3(2), however, no specific function of SCO7328 in growth, differentiation or stress response could be attributed to this anti-sigma factor. These results suggest that BldG is specifically phosphorylated by several anti-sigma factors and it plays a role in the regulation of several sigma factors in S. coelicolor A3(2). This suggests a complex regulation of the stress response and differentiation in S. coelicolor A3(2) through this pleiotropic anti-sigma factor.

Different epithelial cell response to membrane vesicles produced by Listeria monocytogenes cultured with or without salt stress.

We have previously shown that Listeria monocytogenes, a causative agent of listeriosis, can produce membrane vesicles (MVs) during in vitro culture. The aim of this study was to investigate the ability of MVs from L. monocytogenes cultured with or without salt stress to induce cytotoxicity and pro-inflammatory responses in colon epithelial Caco-2 cells. MVs were purified from wild-type L. monocytogenes 10403S strain and an isogenic ΔsigB mutant strain. MVs from both wild-type and ΔsigB mutant strains increased viability of Caco-2 cells regardless of salt stress. Both MVs from wild-type and ΔsigB mutant strains stimulated expression of pro-inflammatory cytokine and chemokine genes in Caco-2 cells. Expression levels of pro-inflammatory cytokine genes in cells treated with MVs from bacteria cultured without salt stress were significantly higher than those in cells treated with MVs from bacteria cultured with salt stress. However, expression levels of chemokine genes in cells treated with MVs from bacteria cultured with salt stress were significantly higher than those in cells treated with MVs from bacteria cultured without salt stress. In addition, expression levels of interleukin (IL)-1ß and IL-8 genes were partially inhibited by either lysozyme-treated MVs or ethylenediaminetetraacetic acid-treated MVs compared to those after treatment with intact MVs. Our results suggest that salt stress can affect the production of L. monocytogenes MVs, thus causing different pro-inflammatory responses in host cells.

Mycobacterium tuberculosis sigE mutant ST28 used as a vaccine induces protective immunity in the guinea pig model.

With more than 9 million new infections and 1.5 million deaths claimed every year, tuberculosis remains one of the major scourges of humankind. The only vaccine available against this disease, the attenuated strain Mycobacterium bovis, BCG is effective against severe forms of the disease in infants, but scarcely effective in protecting adults from the pulmonary form of the disease, thus not stopping transmission. Consequently, the development of an effective anti-tuberculosis vaccine is a major goal for improving global health. The most common concept is that a more effective vaccine should include a first immunization with a live vaccine followed by the administration of an acellular boosting vaccine. In this approach, the live vaccine might be either BCG or a different, more efficient attenuated strain. Recently, we showed that a Mycobacterium tuberculosis mutant missing the gene encoding for the extracellular function sigma factor SigE, is strongly attenuated and is able to induce a more effective protection from M. tuberculosis infection compared to BCG in mice. We now further characterize the protective potential of this novel strain in the guinea pig model of tuberculosis. In the guinea pig, it had limited growth but induced a Th1 immune response and was able to significantly reduce the number of colony forming units as well as prolong survival. Taken together these data provide evidence for the use of the M. tuberculosis sigE mutant as the basis for further development as a vaccine against infection.

The Clostridium difficile Dlt Pathway Is Controlled by the Extracytoplasmic Function Sigma Factor σV in Response to Lysozyme.

Clostridium difficile (also known as Peptoclostridium difficile) is a major nosocomial pathogen and a leading cause of antibiotic-associated diarrhea throughout the world. Colonization of the intestinal tract is necessary for C. difficile to cause disease. Host-produced antimicrobial proteins (AMPs), such as lysozyme, are present in the intestinal tract and can deter colonization by many bacterial pathogens, and yet C. difficile is able to survive in the colon in the presence of these AMPs. Our prior studies established that the Dlt pathway, which increases the surface charge of the bacterium by addition of d-alanine to teichoic acids, is important for C. difficile resistance to a variety of AMPs. We sought to determine what genetic mechanisms regulate expression of the Dlt pathway. In this study, we show that a dlt null mutant is severely attenuated for growth in lysozyme and that expression of the dltDABC operon is induced in response to lysozyme. Moreover, we found that a mutant lacking the extracytoplasmic function (ECF) sigma factor σ(V) does not induce dlt expression in response to lysozyme, indicating that σ(V) is required for regulation of lysozyme-dependent d-alanylation of the cell wall. Using reporter gene fusions and 5' RACE (rapid amplification of cDNA ends) analysis, we identified promoter elements necessary for lysozyme-dependent and lysozyme-independent dlt expression. In addition, we observed that both a sigV mutant and a dlt mutant are more virulent in a hamster model of infection. These findings demonstrate that cell wall d-alanylation in C. difficile is induced by lysozyme in a σ(V)-dependent manner and that this pathway impacts virulence in vivo.

Mucosal vaccination with attenuated Mycobacterium tuberculosis induces strong central memory responses and protects against tuberculosis.

Tuberculosis (TB) is a global pandaemic, partially due to the failure of vaccination approaches. Novel anti-TB vaccines are therefore urgently required. Here we show that aerosol immunization of macaques with the Mtb mutant in SigH (MtbΔsigH) results in significant recruitment of inducible bronchus-associated lymphoid tissue (iBALT) as well as CD4(+) and CD8(+) T cells expressing activation and proliferation markers to the lungs. Further, the findings indicate that pulmonary vaccination with MtbΔsigH elicited strong central memory CD4(+) and CD8(+) T-cell responses in the lung. Vaccination with MtbΔsigH results in significant protection against a lethal TB challenge, as evidenced by an approximately three log reduction in bacterial burdens, significantly diminished clinical manifestations and granulomatous pathology and characterized by the presence of profound iBALT. This highly protective response is virtually absent in unvaccinated and BCG-vaccinated animals after challenge. These results suggest that future TB vaccine candidates can be developed on the basis of MtbΔsigH.

Role for σ38 in prolonged survival of Escherichia coli in Drosophila melanogaster.

Bacteria adapt themselves to host environments by altering the pattern of gene expression. The promoter-recognizing subunit σ of bacterial RNA polymerase plays a major role in the selection of genes to be transcribed. Among seven σ factors of Escherichia coli, σ(38) is responsible for the transcription of genes in the stationary phase and under stressful conditions. We found a transient increase of σ(38) when E. coli was injected into the hemocoel of Drosophila melanogaster. The loss of σ(38) made E. coli rapidly eliminated in flies, and flies infected with σ(38)-lacking E. coli stayed alive longer than those infected with the parental strain. This was also observed in fly lines defective in humoral immune responses, but not in flies in which phagocytosis was impaired. The lack of σ(38) did not influence the susceptibility of E. coli to phagocytosis, but made them vulnerable to killing after engulfment. The changes caused by the loss of σ(38) were recovered by the forced expression of σ(38)-encoding rpoS as well as σ(38)-regulated katE and katG coding for enzymes that detoxify reactive oxygen species. These results collectively suggested that σ(38) contributes to the prolonged survival of E. coli in Drosophila by inducing the production of enzymes that protect bacteria from killing in phagocytes. Considering the similarity in the mechanism of innate immunity against invading bacteria between fruit flies and humans, the products of these genes could be new targets for the development of more effective antibacterial remedies.

[Mucosal immune response to Helicobacter pylori in children with gastroduodenal diseases and allergy].

In children with chronic gastritis/gastroduodenitis, erosions and ulcer of stomach and duodenum and associated allergic diseases (asthma, allergic rhinitis, atopic dermatitis) CagA, sIgA and IgE antibodies to the H. pylori were determined by ELISA in the supernatants of feces. H. pylori infection was determined according to "Maastricht IV". The frequency and contents of CagA did not differ among the groups we studied. However, in children with positive urease test the contents of CagA was significantly higher (p = 0.03) compared with other children. The highest levels of sIgA were found in the feces supernatants from non-allergic children with CG/CGD and were associated with H. pylori infection. The immune response in children with erosions and ulcer of stomach and duodenum and in children with allergy was presented the sIgE to H. pylori. Also, the negative correlation between the level sIgE to H. pylori and content sIgA was found in children with allergy. Thus, increased IgE indicates not only allergy, but also acts as a protective role in the development of anti-infective immunity.

Live recombinant Salmonella Typhi vaccines constructed to investigate the role of rpoS in eliciting immunity to a heterologous antigen.

We hypothesized that the immunogenicity of live Salmonella enterica serovar Typhi vaccines expressing heterologous antigens depends, at least in part, on its rpoS status. As part of our project to develop a recombinant attenuated S. Typhi vaccine (RASTyV) to prevent pneumococcal diseases in infants and children, we constructed three RASTyV strains synthesizing the Streptococcus pneumoniae surface protein PspA to test this hypothesis. Each vector strain carried ten engineered mutations designed to optimize safety and immunogenicity. Two S. Typhi vector strains (chi9639 and chi9640) were derived from the rpoS mutant strain Ty2 and one (chi9633) from the RpoS(+) strain ISP1820. In chi9640, the nonfunctional rpoS gene was replaced with the functional rpoS gene from ISP1820. Plasmid pYA4088, encoding a secreted form of PspA, was moved into the three vector strains. The resulting RASTyV strains were evaluated for safety in vitro and for immunogenicity in mice. All three RASTyV strains were similar to the live attenuated typhoid vaccine Ty21a in their ability to survive in human blood and human monocytes. They were more sensitive to complement and were less able to survive and persist in sewage and surface water than their wild-type counterparts. Adult mice intranasally immunized with any of the RASTyV strains developed immune responses against PspA and Salmonella antigens. The RpoS(+) vaccines induced a balanced Th1/Th2 immune response while the RpoS(-) strain chi9639(pYA4088) induced a strong Th2 immune response. Immunization with any RASTyV provided protection against S. pneumoniae challenge; the RpoS(+) strain chi9640(pYA4088) provided significantly greater protection than the ISP1820 derivative, chi9633(pYA4088). In the pre-clinical setting, these strains exhibited a desirable balance between safety and immunogenicity and are currently being evaluated in a Phase 1 clinical trial to determine which of the three RASTyVs has the optimal safety and immunogenicity profile in human hosts.

Altered cellular infiltration and cytokine levels during early Mycobacterium tuberculosis sigC mutant infection are associated with late-stage disease attenuation and milder immunopathology in mice.

BACKGROUND: Mouse virulence assessments of certain Mycobacterium tuberculosis mutants have revealed an immunopathology defect in which high tissue CFU counts are observed but the tissue pathology and lethality are reduced. M. tuberculosis mutants which grow and persist in the mouse lungs, but have attenuated disease progression, have the immunopathology (imp) phenotype. The antigenic properties of these strains may alter the progression of disease due to a reduction in host immune cell recruitment to the lungs resulting in disease attenuation and prolonged host survival. RESULTS: In this study we focused on the mouse immune response to one such mutant; the M. tuberculosis Delta sigC mutant. Aerosol infection of DBA/2 and SCID mice with the M. tuberculosis Delta sigC mutant, complemented mutant and wild type strain showed proliferation of mutant bacilli in mouse lungs, but with decreased inflammation and mortality in DBA/2 mice. SCID mice shared the same phenotype as the DBA/2 mice in response to the Delta sigC mutant, however, they succumbed to the infection faster. Bronchoalveolar lavage (BAL) fluid analysis revealed elevated numbers of infiltrating neutrophils in the lungs of mice infected with wild type and complemented Delta sigC mutant strains but not in mice infected with the Delta sigC mutant. In addition, DBA/2 mice infected with the Delta sigC mutant had reduced levels of TNF-alpha, IL-1beta, IL-6 and IFN-gamma in the lungs. Similarly, there was a reduction in proinflammatory cytokines in the lungs of SCID mice. In contrast to the mouse model, the Delta sigC mutant had reduced initial growth in guinea pig lungs. A possible mechanism of attenuation in the Delta sigC mutant may be a reduction in neutrophilic-influx in the alveolar spaces of the lungs, and decreased proinflammatory cytokine secretion. In contrast to mouse data, the M. tuberculosis Delta sigC mutant proliferates slowly in guinea pig lungs, a setting characterized by caseating necrosis. CONCLUSION: Our observations suggest that the immunopathology phenotype is associated with the inability to trigger a strong early immune response, resulting in disease attenuation. While macrophages and T cells have been shown to be important in containing M. tuberculosis disease our study has shown that neutrophils may also play an important role in the containment of this organism.

Characterization of the Mycobacterium tuberculosis sigma factor SigM by assessment of virulence and identification of SigM-dependent genes.

Alternate sigma factors have been implicated in the survival of mycobacteria in response to specific stresses. To characterize the role of SigM in Mycobacterium tuberculosis, a sigM deletion mutant was generated by allelic exchange in the virulent CDC1551 strain. Comparing the wild-type and Delta sigM strains by complete genomic microarray, we observed a low level of baseline expression of sigM in wild-type M. tuberculosis and no significant differences in the gene expression patterns between these two strains. Alternatively, a SigM-overexpressing M. tuberculosis strain was constructed and microarray profiling revealed SigM-dependent expression of a relatively small group of genes, which included four esat-6 homologues: esxE, esxF, esxT, and esxU. An assessment of SigM-dependent promoters from the microarray analysis revealed a putative consensus sequence for M. tuberculosis SigM of -35 GGAAC and -10 CGTCR. In vitro expression studies showed that M. tuberculosis sigM transcripts accumulate slightly in stationary phase and following heat shock. To understand the role of SigM in pathogenesis, the M. tuberculosis sigM deletion strain was compared with the isogenic wild-type strain and the complemented mutant strain for survival in murine macrophages and in the mouse model. The mutant was found to have similar abilities to survive in both the resting and activated J774A.1 macrophages. Mouse organ bacterial burdens indicated that the mutant proliferated and persisted at the same level as that of the wild-type and complemented strains in lung and spleen tissues. In time-to-death experiments in the mouse model, the Delta sigM mutant exhibited lethality times comparable to those observed for the wild-type and complemented strains. These data indicate that M. tuberculosis SigM governs the expression of a small set of genes, including four esat-6 homologues, and that the loss of sigM does not confer a detectable virulence defect in the macrophages and mouse models of infection.

The alternative sigma factor sigmaB of Bacillus cereus: response to stress and role in heat adaptation.

A gene cluster encoding the alternative sigma factor sigma(B), three predicted regulators of sigma(B) (RsbV, RsbW, and RsbY), and one protein whose function is not known (Orf4) was identified in the genome sequence of the food pathogen Bacillus cereus ATCC 14579. Western blotting with polyclonal antibodies raised against sigma(B) revealed that there was 20.1-fold activation of sigma(B) after a heat shock from 30 to 42 degrees C. Osmotic upshock and ethanol exposure also upregulated sigma(B), albeit less than a heat shock. When the intracellular ATP concentration was decreased by exposure to carbonyl cyanide m-chlorophenylhydrazone (CCCP), only limited increases in sigma(B) levels were observed, revealing that stress due to ATP depletion is not an important factor in sigma(B) activation in B. cereus. Analysis of transcription of the sigB operon by Northern blotting and primer extension revealed the presence of a sigma(B)-dependent promoter upstream of the first open reading frame (rsbV) of the sigB operon, indicating that transcription of sigB is autoregulated. A second sigma(B)-dependent promoter was identified upstream of the last open reading frame (orf4) of the sigB operon. Production of virulence factors and the nonhemolytic enterotoxin Nhe in a sigB null mutant was the same as in the parent strain. However, sigma(B) was found to play a role in the protective heat shock response of B. cereus. The sigB null mutant was less protected against the lethal temperature of 50 degrees C by a preadaptation to 42 degrees C than the parent strain was, resulting in a more-than-100-fold-reduced survival of the mutant after 40 min at 50 degrees C.

Intestinal colonisation-inhibition and virulence of Salmonella phoP, rpoS and ompC deletion mutants in chickens.

Administration of live Salmonella strains to day-old chicks provides profound protection against superinfection with a related strain within a matter of hours by a colonisation-inhibition mechanism, which is primarily a bacterial physiological process. Although currently available, commercial, live attenuated Salmonella vaccines induce protection by adaptive immunity, none of them is able to induce protection against Salmonella organisms by colonisation-inhibition and, therefore, they are unable to protect newly-hatched birds immediately after oral vaccination. In this study, mutants of Salmonella Typhimurium and Enteritidis with deletions in phoP and rpoS, either alone or in combination with ompC, were characterised and tested for their level of attenuation and their ability to inhibit the intestinal colonisation of the isogenic parent strains in chickens. Mutants with deletions only in rpoS demonstrated an unaffected potential to inhibit the intestinal colonisation of the challenge strain but were still fully virulent for the chickens. Mutants with deletions in phoP, either alone or in combination with rpoS, resulted in a high level of attenuation, unimpaired ability to colonise the gut and a nearly unaffected potential to inhibit the challenge strain from caecal colonisation. Mutants with an additional deletion in ompC revealed a reduced capacity of intestinal colonisation-inhibition when compared to the control strains and both the single rpoS and the phoP deletion mutants. Mutations in phoP- or phoP-regulated genes may therefore be used for the development of live attenuated Salmonella vaccines possessing these novel characteristics.

A nucleus-encoded maize protein with sigma factor activity accumulates in mitochondria and chloroplasts.

Plants contain nuclear gene families that encode proteins related to the principal sigma factors of eubacteria. As sigma factors function in transcription, the plant proteins have been presumed or demonstrated to associate with the eubacteria-like RNA polymerase of chloroplasts. In maize, five sig cDNA sequences have been reported, and four of the products are present in plastids as predicted. However, in vitro chloroplast import assays and computer algorithms gave ambiguous results with the fifth protein, ZmSig2B. Unlike the other maize sigma factors, ZmSig2B is expressed throughout developing seedling leaves, as well as in roots and etiolated tissues. To determine the subcellular location of ZmSig2B, we have now used immunoblot assays to show that it co-purifies with both mitochondria and plastids. Its NH2-terminal 153 amino acids, translationally fused to green fluorescent protein (GFP), targeted GFP to chloroplasts and mitochondria in bombarded maize leaves. A putative role for ZmSig2B in mitochondrial transcription is supported by its presence in a maize mitochondrial transcription extract. ZmSig2B also exhibits the expected properties of a chloroplast sigma factor: recombinant ZmSig2B binds to a chloroplast promoter and initiates transcription in vitro when combined with Escherichia coli core RNA polymerase. Therefore ZmSig2B is an unusual nucleus-encoded sigma factor that appears to function in both chloroplasts and mitochondria.

Comparison of the abilities of Salmonella typhimurium rpoS, aroA and rpoS aroA strains to elicit humoral immune responses in BALB/c mice and to cause lethal infection in athymic BALB/c mice.

Salmonella typhimurium rpoS and rpoS aroA mutants are effective live vaccines in the murine model of salmonellosis (Coynault et al., Mol. Microbiol. 1996; 22: 149-60). Here, we further investigate the characteristics of these vaccines. The systemic humoral response induced by S. typhimurium rpoS, aroA and rpoS aroA vaccine candidates against S. typhimurium LPS was studied by ELISA. In BALB/c mice, the rpoS aroA strain induced a systemic anti-LPS humoral response similar to that induced by the rpoS and aroA strains. The virulence of aroA and rpoS aroA vaccines in nude (nu/nu) BALB/c mice was also compared. Salmonella typhimurium aroA and rpoS aroA vaccines both produced slowly progressing lethal infections in athymic mice inoculated i.p. but the rpoS aroA strain was more attenuated than the aroA strain, as determined by time to death and bacterial counts in spleens. Finally, a rpoS mutant of Salmonella dublin conferred protection in mice against an oral challenge with a wild-type strain of S. dublin whereas a rpoS mutant of S. typhimurium did not. This suggests that the protection provided by the S. typhimurium rpoS vaccine is serotype-dependent.

Correlation between chlamydial infection and autoimmune response: molecular mimicry between RNA polymerase major sigma subunit from Chlamydia trachomatis and human L7.

L7 is one of the ribosomal proteins frequently targeted by autoantibodies in rheumatic autoimmune diseases. A computer search revealed a region within the immunodominant epitope of L7 (peptide II) that is highly homologous to amino acid sequence 264-286 of the RNA polymerase major sigma factor of the eubacterium Chlamydia trachomatis. Anti-L7 autoantibodies affinity purified from the immunodominant epitope were able to recognize this sequence as they reacted with purified recombinant sigma factor. Immunofluorescence labeling experiments on C. trachomatis lysates revealed a punctate staining pattern of numerous spots when incubated with the affinity-purified anti-peptide II autoantibodies. Binding of autoantibodies to peptide II was inhibited by the homologous sigma peptide. This is the first demonstration of epitope mimicry between a human and a chlamydial protein on the level of B cells. Antibody screening revealed a significant correlation between the presence of anti-L7 autoantibodies and C. trachomatis infection in patients with systemic lupus erythematosus and mixed connective tissue disease. Our results suggest that molecular mimicry is involved in the initiation of anti-L7 autoantibody response and may represent a first glance into the immunopathology of Chlamydia with respect to systemic rheumatic diseases.

Bacillus licheniformis sigB operon encoding the general stress transcription factor sigma B.

The general stress response of the Gram-positive soil bacterium Bacillus subtilis is controlled by the sigma B transcription factor. sigma B activity is regulated by the newly discovered partner switching mechanism of signal transduction, which integrates the two different classes of challenges which posttranslationally activate sigma B: environmental stress and energy stress. Our investigation of a possible sigma B homologue in the related soil bacterium B. licheniformis had two goals. First, this study would contribute to understanding the distribution of the sigma B general stress system among Gram-positive bacteria. Second, a phylogenetic comparison of regulatory systems can supplement genetic and biochemical analysis by revealing conserved features that are critical for function. We report here that (1) B. licheniformis cells contain a protein that closely resembles B. subtilis sigma B in size and antigenic properties; (2) the level of this potential sigma B homologue rapidly increases following environmental or energy stress; and (3) the B. licheniformis genome encodes a homologue of the sigB general stress operon, including the sigma B structural gene and seven rsb regulatory genes. Based on these results, B. licheniformis possesses a general stress system likely regulated by two coupled partner switching modules that sense and integrate the two broad classes of activating stress signals.

The pathogenic neisseriae contain an inactive rpoN gene and do not utilize the pilE sigma54 promoter.

The sigma54 promoter (P3) upstream of the pilE gene in Neisseria gonorrhoeae was shown to be non-functional by transcriptional analysis of a PpilE::lacZ fusion containing only P3. A region on the chromosome of N. gonorrhoeae strain MS11-A was identified that potentially encodes a protein with a significant similarity to the Escherichia coli RpoN protein. However, this region (designated RLS for rpoN-like sequence) does not contain a single open reading frame (ORF) capable of encoding a functional RpoN protein. It appears that RLS may have arisen from an ancestral rpoN homologue that underwent a deletion removing the sequence encoding the essential helix-turn-helix (HTH) motif, and changing the subsequent reading frame. An RLS has been identified in several strains of N. gonorrhoeae and N. meningitidis. A 90-kDa gonococcal protein has previously been shown to react with a monoclonal antibody raised against the RpoN from Salmonella typhimurium. However, mutagenesis and Western blot analysis confirmed that the gene encoding this protein is not contained within RLS.

In vitro transcription of Myxococcus xanthus genes with RNA polymerase containing sigmaA, the major sigma factor in growing cells.

Myxococcus xanthus is a Gram-negative bacterium that undergoes multicellular development upon starvation. We have developed a simple and rapid procedure for partial purification of RNA polymerase from growing M. xanthus cells, using heparin-agarose and DNA-cellulose chromatographies. In addition to core subunits, the enzyme contains one fairly abundant polypeptide of approximately 105 kDa. We have shown by Western blot analysis and protein sequencing that the 105-kDa polypeptide is sigmaA, the product of the M. xanthus sigA gene. Partially purified sigmaA RNA polymerase, or holoenzyme reconstituted from sigmaA and core RNA polymerase, transcribed in vitro the vegA and aphII genes that are known to be expressed in growing M. xanthus cells. Reconstituted sigmaA RNA polymerase produced vegA mRNA in vitro with the same 5' end as vegA mRNA produced in vivo, demonstrating that initiation of transcription was accurate in vitro. These results provide biochemical evidence that sigmaA is the major vegetative sigma factor of M. xanthus. To our knowledge, this is the first report of in vitro transcription of M. xanthus chromosomal genes, providing a foundation for further biochemical analysis of transcriptional regulatory mechanisms in a microbe that relies extensively on cell-cell interactions.