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P Zuber

Publications and source records attributed to P Zuber.

At least 19 recordsLinked to original sources
PubMed2001

A peptide profile of the Bacillus subtilis genome.

Bacillus subtilis is known to produce an abundance of small polypeptides. Several of these have antimicrobial activity and others are pheromones or extracellular factors that affect internal signal transduction systems. The completion of the B. subtilis genomic nucleotide sequence has revealed 345 small polypeptide open-reading frames (of 85 codons or less), 81% of which are of unknown function. A significant number of these reside in prophage genomes or phage-like elements where they can be organized into large operons. It is likely that many more exist in the genome of B. subtilis but are "hidden" entirely or partially within other reading frames, or possess non-conventional translation start signals and have escaped detection. The discovery of so many small polypeptide orfs (SPORFs) and the likelihood of many more pose a challenging problem for those undertaking the complete functional analysis of genes that constitute prokaryotic genomes. A survey of known and potential peptide-encoding reading frames is presented herein as an attempt to classify those that are found in the B. subtilis genome according to function inferred from homology searches and to conservation among products of other microbial genomes.

Amino Acid Sequence↗
PubMed2001

Loss-of-function mutations in yjbD result in ClpX- and ClpP-independent competence development of Bacillus subtilis.

Mutations in clpP and clpX have pleiotropic effects on growth and developmentally regulated gene expression in Bacillus subtilis. ClpP and ClpX are needed for expression of comK, encoding the competence transcription factor required for the expression of genes within the competence regulon. ClpP, in combination with the ATPase ClpC, degrades the inhibitor of ComK, MecA. Proteolysis of MecA is stimulated by a small protein, ComS, which interacts with MecA. Suppressor mutations (cxs) were isolated that bypass the requirement for clpX for comK expression. These were found also to overcome the defect in comK expression conferred by a clpP mutation. These mutations were identified as missense mutations (cxs-5, -7 and -12) and a nonsense (UAG) codon substitution (cxs-10) in the yjbD coding sequence in a locus linked to mecA. That a yjbD disruption confers the cxs phenotype, together with its complementation by an ectopically expressed copy of yjbD, indicated that the suppressor alleles bear recessive, loss-of-function mutations of yjbD. ClpP- and ClpX-independent comK expression rendered by inactivation of yjbD was still medium-dependent and required ComS. MecA levels in a clpP-yjbD mutant were lower that those of clpP mutant cells and ComK protein concentration in the clpP mutant was restored to wild-type levels by the yjbD mutation. Consequently, the yjbD mutation bypasses the defect in competence development conferred by clpP and clpX. YjbD protein is barely detectable in wild-type cells, but is present in large amounts in the clpP mutant cells. The results suggest that the role of ClpP in competence development is to degrade YjbD protein so that ComS can productively interact with the MecA-ClpC-ComK complex. Alternatively, the result could suggest that YjbD has a negative effect on regulated proteolysis and that MecA is degraded independently of ClpP when YjbD is absent.

ATPases Associated with Diverse Cellular Activitie↗
PubMed2000

Mutations conferring amino acid residue substitutions in the carboxy-terminal domain of RNA polymerase alpha can suppress clpX and clpP with respect to developmentally regulated transcription in Bacillus subtilis.

The Bacillus subtilis clpX and clpP genes are the sites of pleiotropic mutations that adversely affect growth on a variety of media and impair developmental processes such as sporulation and competence development. ClpX is necessary for the post-exponential induction of genes that require the sigmaH form of RNA polymerase for transcription. Both ClpX and ClpP are required for the activation of sigmaA-dependent transcription of the srf operon that encodes surfactin synthetase and the regulatory peptide ComS, required for the development of genetic competence. Transcription of srf is activated by the two-component regulatory system ComPA in response to the peptide pheromone, ComX, which mediates cell density-dependent control. A clpX mutant, although able to produce ComX, is unable to respond to the pheromone. A mutant allele of comP, encoding a product whose activity is independent of ComX, is not able to suppress clpX with respect to srf expression, suggesting that ClpXP acts at the level of ComA-dependent activation of srf transcription initiation. Suppressor mutations of clpX (cxs-1 and cxs-2) were isolated in screens for pseudorevertants exhibiting high levels of srf expression and sigmaH-dependent transcription respectively. One mutation, cxs-1, suppressed a clpP null mutation with respect to srf transcription, but did not overcome the block conferred by clpP on competence development and sporulation. Both cxs-1 and cxs-2 mutations map to the region of the rpoA gene encoding the RNA polymerase alpha C-terminal domain (alphaCTD). The reconstruction of the cxs-1 and cxs-2 alleles of rpoA confirmed that these mutations confer the suppressor phenotype. These findings provide further support for the hypothesis that ClpX and ClpP might be intimately associated with transcription initiation in B. subtilis.

ATPases Associated with Diverse Cellular Activitie↗
PubMed2000

The ClpX protein of Bacillus subtilis indirectly influences RNA polymerase holoenzyme composition and directly stimulates sigma-dependent transcription.

In Bacillus subtilis, several processes associated with the onset of stationary phase, including the initiation of sporulation, require the activity of the minor sigmaH form of RNA polymerase (RNAP). The induction of sigmaH-dependent gene transcription requires the regulatory ATPase, ClpX. The ClpX-dependent post-exponential increase in sigmaH activity is not dependent on the activator of sporulation gene expression, Spo0A. By determining the level of sigmaH and sigmaA in whole-cell extracts and RNAP preparations, evidence is presented that clpX does not influence the concentration of sigma subunits, but is required for the stationary phase reduction in sigmaA-RNAP holoenzyme. This is probably an indirect consequence of ClpX activity, because the ClpX-dependent decrease in sigmaA-RNAP concentration does not occur in a spo0A abrB mutant. The addition of ClpX to in vitro transcription reactions resulted in the stimulation of RNAP holoenzyme activity, but sigmaH-RNAP was observed to be more sensitive to ClpX-dependent stimulation than sigmaA-RNAP. No difference in transcriptional activity was observed in single-cycle in vitro transcription reactions, suggesting that ClpX acted at a step in transcription initiation after closed- and open-promoter complex formation. ClpX is proposed to function indirectly in the displacement of sigmaA from core RNAP and to act directly in the stimulation of sigmaH-dependent transcription in sporulating B. subtilis cells.

ATPases Associated with Diverse Cellular Activitie↗
PubMed2000

Mutational analysis of the sbo-alb locus of Bacillus subtilis: identification of genes required for subtilosin production and immunity.

The Bacillus subtilis 168 derivative JH642 produces a bacteriocin, subtilosin, which possesses activity against Listeria monocytogenes. Inspection of the amino acid sequence of the presubtilosin polypeptide encoded by the gene sboA and sequence data from analysis of mature subtilosin indicate that the precursor subtilosin peptide undergoes several unique and unusual chemical modifications during its maturation process. The genes of the sbo-alb operon are believed to function in the synthesis and maturation of subtilosin. Nonpolar mutations introduced into each of the alb genes resulted in loss or reduction of subtilosin production. sboA, albA, and albF mutants showed no antilisterial activity, indicating that the products of these genes are critical for the production of active subtilosin. Mutations in albB, -C, and -D resulted in reduction of antilisterial activity and decreased immunity to subtilosin, particularly under anaerobic conditions. A new gene, sboX, encoding another bacteriocin-like product was discovered residing in a sequence overlapping the coding region of sboA. Construction of an sboX-lacZ translational fusion and analysis of its expression indicate that sboX is induced in stationary phase of anaerobic cultures of JH642. An in-frame deletion of the sboX coding sequence did not affect the antilisterial activity or production of or immunity to subtilosin. The results of this investigation show that the sbo-alb genes are required for the mechanisms of subtilosin synthesis and immunity.

Amino Acid Sequence↗
PubMed2000

Dual control of sbo-alb operon expression by the Spo0 and ResDE systems of signal transduction under anaerobic conditions in Bacillus subtilis.

The Bacillus subtilis sbo-alb operon contains sboA, the structural gene for the bacteriocin subtilosin, and the alb genes required for subtilosin production. Transcription from the sbo-alb promoter is highly induced by oxygen limitation. The transcriptional regulation of the sbo-alb operon is under dual control involving the transition state regulator AbrB and the two-component regulatory proteins ResD and ResE.

Anaerobiosis↗
PubMed2000

Tuberculin skin testing to assess the occupational risk of Mycobacterium tuberculosis infection among health care workers in Abidjan, Côte d'Ivoire.

SETTING: Tuberculin skin test (TST) survey of health care workers (HCWs) in selected clinical services in Abidjan, Côte d'Ivoire. OBJECTIVE: To assess whether HCWs in Abidjan are at increased risk for occupationally acquired Mycobacterium tuberculosis infection. DESIGN: From October 1996 to January 1997, consenting HCWs from four services where tuberculosis (TB) prevalence among patients was high and two services where it was low were evaluated with a questionnaire, TST (including evaluation of anergy) and chest radiograph. RESULTS: Of the 512 participants, 405 (79%) had a TST reaction of > or =10 mm, eight (2%) were anergic, five (1%) had a radiograph compatible with TB, and two had confirmed TB. Using a cut-off of 10 mm, we found a higher prevalence of TST positivity in services with high TB prevalence than in those with low TB prevalence (92% vs 72%; odds ratio [OR] 4.3; 95% confidence interval [CI] 2.3-8.0]) and among HCWs with direct (87%; OR 2.9; 95%CI 1.6-5.1) and indirect patient contact (80%, OR 1.7; 95%CI 1.0-2.3) than among those with minimal patient contact (69%). CONCLUSION: These findings indicate that TST positivity among HCWs is related to level of exposure to TB patients, and suggest that HCWs in Abidjan are at risk for the nosocomial transmission of TB.

Adult↗
PubMed1999

Mutational analysis of ComS: evidence for the interaction of ComS and MecA in the regulation of competence development in Bacillus subtilis.

The development of Bacillus subtilis genetic competence is a highly regulated adaptive response to stationary-phase stress. A key step in competence development is the activation of the transcriptional regulator ComK, which is required for the expression of genes encoding the products that function in DNA uptake. In log-phase cultures, ComK is trapped in a complex composed of MecA and ClpC, in which it is rendered inactive. The comS gene, contained within the srf operon, is induced in response to high culture cell density and nutritional stress. Its product functions to release active ComK from the complex, allowing ComK to stimulate the transcription initiation of its own gene as well as that of the late competence operons. Western analysis showed that ComS accumulates to maximal levels between T3 and T4, mirroring the pattern of competence cell development and late competence gene expression. Experiments to examine the target of ComS activity in vitro showed that ComS binds to MecA. This is further supported by coimmunoprecipitation using anti-MecA antiserum. To clarify the role of ComS in competence regulation, a system for evaluating the effect of comS and mutant derivatives on the expression of comG, one of the late competence operons, was constructed. comS mutations, created by alanine-scanning mutagenesis, that significantly reduced comG-lacZ expression were clustered within two regions, one at the N-terminus and the other at the C-terminus of ComS. ComSI13 --> A and ComSW43 --> A were selected for further analysis as representative mutants for both regions required for ComS activity. We observed that ComSI13 --> A showed significantly reduced affinity for MecA, whereas ComSW43 --> A showed near normal binding affinity for MecA. The results show that binding to MecA is critical for ComS function, but do not rule out the possibility that ComS possesses other activities.

Alleles↗
PubMed1999

Role of lon and ClpX in the post-translational regulation of a sigma subunit of RNA polymerase required for cellular differentiation in Bacillus subtilis.

The RNA polymerase sigma subunit, sigmaH (Spo0H) of Bacillus subtilis, is essential for the transcription of genes that function in sporulation and genetic competence. Although spo0H is transcriptionally regulated by the key regulatory device that controls sporulation initiation, the Spo0 phosphorelay, there is considerable evidence implicating a mechanism of post-translational control that governs the activity and concentration of sigmaH. Post-translational control of spo0H is responsible for the reduced expression of genes requiring sigmaH under conditions of low environmental pH. It is also responsible for heightened sigmaH activity upon relief of acid stress and during nutritional depletion. In this study, the ATP-dependent proteases LonA and B and the regulatory ATPase ClpX were found to function in the post-translational control of sigmaH. Mutations in lonA and lonB result in elevated sigmaH protein concentrations in low-pH cultures. However, this is not sufficient to increase sigmaH-dependent transcription. Activation of sigmaH-dependent transcription upon raising medium pH and in cells undergoing sporulation requires clpX, as shown by measuring the expression of lacZ fusions that require sigmaH for transcription and by complementation of a clpX null mutation. A hypothesis is presented that low environmental pH results in the Lon-dependent degradation of sigmaH, but the activity of sigmaH in sporulating cells and in cultures at neutral pH is stimulated by a ClpX-dependent mechanism in response to nutritional stress.

ATP-Dependent Proteases↗
PubMed1999

A mutation in the 3-phosphoglycerate kinase gene allows anaerobic growth of Bacillus subtilis in the absence of ResE kinase.

The Bacillus subtilis ResD-ResE two-component signal transduction system is essential for aerobic and anaerobic respiration. A spontaneous suppressor mutant that expresses ResD-controlled genes and grows anaerobically in the absence of the ResE histidine kinase was isolated. In addition, aerobic expression of ResD-controlled genes in the suppressed strain was constitutive and occurred at a much higher level than that observed in the wild-type strain. The suppressing mutation, which mapped to pgk, the gene encoding 3-phosphoglycerate kinase, failed to suppress a resD mutation, suggesting that the suppressing mutation creates a pathway for phosphorylation of the response regulator, ResD, which is independent of the cognate sensor kinase, ResE. The pgk-1 mutant exhibited very low but measurable 3-phosphoglycerate kinase activity compared to the wild-type strain. The results suggest that accumulation of a glycolytic intermediate, probably 1, 3-diphosphoglycerate, is responsible for the observed effect of the pgk-1 mutation on anaerobiosis of resE mutant cells.

Aerobiosis↗
PubMed1999

Genes of the sbo-alb locus of Bacillus subtilis are required for production of the antilisterial bacteriocin subtilosin.

Bacillus subtilis JH642 and a wild strain of B. subtilis called 22a both produce an antilisterial peptide that can be purified by anion-exchange and gel filtration chromatography. Amino acid analysis confirmed that the substance was the cyclic bacteriocin subtilosin. A mutant defective in production of the substance was isolated from a plasmid gene disruption library. The plasmid insertion conferring the antilisterial-peptide-negative phenotype was located in a seven-gene operon (alb, for antilisterial bacteriocin) residing immediately downstream from the sbo gene, which encodes the precursor of subtilosin. An insertion mutation in the sbo gene also conferred loss of antilisterial activity. Comparison of the presubtilosin and mature subtilosin sequences suggested that certain residues undergo unusual posttranslational modifications unlike those occurring during the synthesis of class I (lantibiotic) or some class II bacteriocins. The putative products of the genes of the operon identified show similarities to peptidases and transport proteins that may function in processing and export. Two alb gene products resemble proteins that function in pyrroloquinoline quinone biosynthesis. The use of lacZ-alb and lacZ-sbo gene fusions, along with primer extension analysis, revealed that the sbo-alb genes are transcribed from a major promoter, residing upstream of sbo, that is very likely utilized by the sigma(A) form of RNA polymerase. The sbo and alb genes are negatively regulated by the global transition state regulator AbrB and are also under positive autoregulation that is not mediated by the subtilosin peptide but instead requires one or more of the alb gene products.

Amino Acid Sequence↗
PubMed1999

Epidemiology of persistent tuberculosis in DeKalb County, Georgia, 1990-1996.

BACKGROUND: In DeKalb County, Georgia, during 1990 to 1996, tuberculosis incidence rates fluctuated between 15.3 cases/100,000 person-years (PY) and 19.2 cases/100,000 PY. These rates are approximately 1.5 to 2 times higher than those measured for the United States as a whole, and do not reflect the decline observed nationally since 1993. We reviewed DeKalb tuberculosis registry to investigate risk factors for tuberculosis and describe trends of tuberculosis incidence over time. METHODS: We compared average annual tuberculosis case counts and incidence rates in DeKalb before and after 1993. We calculated rates of tuberculosis incidence using race, age and sex stratified population estimates from the U.S. Bureau of the Census. We compared these rates for the periods 1990-1992 and 1993-1996 using Poisson regressions. RESULTS: Between both time periods, tuberculosis case counts decreased by 6% among whites, by 2% among blacks, and increased by 34% among Asians. Despite this large increase in case numbers, tuberculosis incidence rates among Asians only increased by 4%. For all three race groups, tuberculosis incidence almost doubled for those younger than 15 years of age. CONCLUSIONS: Trends of tuberculosis incidence in DeKalb County varied between different population groups. Migration from countries with a high prevalence of tuberculosis accounted for a larger number of foreign-born cases in recent years. However, increasing tuberculosis incidence rates found among the youngest age groups suggest that active transmission of Mycobacterium tuberculosis also took place.

Adolescent↗
PubMed1998

Stoichiometry and specificity of in vitro phosphopantetheinylation and aminoacylation of the valine-activating module of surfactin synthetase.

Surfactin synthetase is the enzyme responsible for biosynthesis of the lipoheptapeptide antibiotic surfactin by Bacillus subtilis. Fragments of SrfB1, the L-valine-activating module of the second subunit of surfactin synthetase, were overproduced in Escherichia coli. In addition to a 143-kDa SrfB1 fragment that contains four domains putatively involved in activation (adenylation domain), autoaminoacylation (peptidyl carrier protein (PCP) domain), and peptide bond formation (two condensation domains), subfragments comprising two domains (104-kDa condensation-adenylation and 73-kDa adenylation-PCP), and one domain (18-kDa PCP) were also overproduced in and purified from E. coli as N-terminal hexahistidine fusion proteins. Incubation of these domains with pure Sfp, a phosphopantetheinyl transferase (PPTase) from B. subtilis, and CoA allowed quantitation of posttranslational phosphopantetheinylation of Ser999 by mass spectrometry for the 18-kDa PCP fragment and by radioassay using cosubstrate [3H] pantetheinyl-coenzyme A for all PCP-containing constructs. The phosphopantetheine stoichiometry correlated with the subsequent mole fractions of [14C] valyl groups that could be covalently transferred to these holo-PCP domains. In turn, the catalytic efficiency of intramolecular aminoacylation of the 143-kDa fragment could be compared with the reaction "in trans" between adenylation and PCP fragments of SrfB1. The corresponding holo-PCP domain of the next module, SrfB2, was not detectably aminoacylated by SrfB1, indicative of protein-protein recognition between adenylation and cognate PCP domains. These results should permit future exploration of the timing and specificity of peptide bond formation by this class of biosynthetic enzymes.

Acylation↗
PubMed1998

Characterization of Sfp, a Bacillus subtilis phosphopantetheinyl transferase for peptidyl carrier protein domains in peptide synthetases.

The Bacillus subtilis enzyme Sfp, required for production of the lipoheptapeptide antibiotic surfactin, posttranslationally phosphopantetheinylates a serine residue in each of the seven peptidyl carrier protein domains of the first three subunits (SrfABC) of surfactin synthetase to yield docking sites for amino acid loading and peptide bond formation. With recombinant Sfp and 16-17-kDa peptidyl carrier protein (PCP) domains excised from the SrfB1 and SrfB2 modules as apo substrates, kcat values of 56-104 min-1 and K(m) values of 1.3-1.8 microM were determined, indicating equivalent recognition of the adjacent PCP domains by Sfp. In contrast to other phosphopantetheinyl transferases (PPTases) previously examined, Sfp will modify the apo forms of heterologous recombinant proteins, including the PCP domain of Saccharomyces cerevisiae Lys2 (involved in lysine biosynthesis), the aryl carrier protein (ArCP) domain of Escherichia coli EntB (involved in enterobactin biosynthesis), and the E. coli acyl carrier protein (ACP) subunit, suggesting Sfp as a good candidate for heterologous coexpression with peptide and polyketide synthase genes to overproduce holo-synthase enzymes. Cosubstrate coenzyme A (CoA), the phosphopantetheinyl group donor, has a K(m) of 0.7 microM. Desulfo-CoA and homocysteamine-CoA are also substrates of Sfp, and benzoyl-CoA and phenylacetyl-CoA are also utilized by Sfp, resulting in direct transfer of acyl phosphopantetheinyl moieties into the carrier protein substrate. Mutagenesis in Sfp of five residues conserved across the PPTase family was assessed for in vivo effects on surfactin production and in vitro effects on PPTase activity.

Amino Acid Sequence↗
PubMed1998

Anaerobic regulation of Bacillus subtilis Krebs cycle genes.

Krebs cycle enzyme activity in Bacillus subtilis was examined under aerobic and anaerobic conditions. Citrate synthase and aconitase activities in cells grown anaerobically in the presence of nitrate were reduced by as much as 10- and 30-fold, respectively, from levels observed under aerobic culture conditions. The maximum level of isocitrate dehydrogenase activity during anaerobic growth was only twofold lower than that in aerobic cultures. These reductions in activity under conditions of anaerobiosis were found to be primarily the result of reduced Krebs cycle gene transcription. This repression was not dependent on either the fnr or resDE gene products, which have been shown to regulate expression of other B. subtilis genes in response to anaerobic conditions. Additionally, catabolite control proteins CcpA and CcpB were not responsible for the repression. A dyad symmetry element located between positions -73 and -59 relative to the transcription start site of the aconitase gene (citB) promoter was previously shown to be a target of catabolite repression and the binding site for a putative negative regulator during aerobic growth. The deletion of the upstream arm of the dyad symmetry region abolished the citB repression observed during anaerobic growth. Furthermore, neither citZ or citB was repressed in an anaerobically grown citB mutant, an effect that was very likely the result of citrate accumulation. These results suggest that catabolite repression and anaerobic repression of citZ and citB are regulated by a common mechanism that does not involve CcpA, CcpB, Fnr, or ResDE.

Aconitate Hydratase↗
PubMed1998

A molecular switch controlling competence and motility: competence regulatory factors ComS, MecA, and ComK control sigmaD-dependent gene expression in Bacillus subtilis.

Bacillus subtilis, like many bacteria, will choose among several response pathways when encountering a stressful environment. Among the processes activated under growth-restricting conditions are sporulation, establishment of motility, and competence development. Recent reports implicate ComK and MecA-ClpC as part of a system that regulates both motility and competence development. MecA, while negatively controlling competence by inhibiting ComK, stimulates sigmaD-dependent transcription of genes that function in motility and autolysin production. Both ComK-dependent and -independent pathways have been proposed for MecA's role in the regulation of motility. Mutations in mecA reduce the transcription of hag. encoding flagellin, and are partially suppressed by comK in both medium promoting motility and medium promoting competence. Reduced sigmaD levels are observed in mecA mutants grown in competence medium, but no change in sigmaD concentration is detected in a comK mutant. The comF operon, transcription of which requires ComK, is located immediately upstream of the operon that contains the flgM gene, encoding the sigmaD-specific antisigma factor. An insertion mutation that disrupts the putative comF-flgM transcription unit confers a phenotype identical to that of the comK mutant with respect to hag-lacZ expression. Expression of a flgM-lacZ operon fusion is reduced in both sigD and comK mutant cells but is abolished in the sigD comK double mutant. Reverse transcription-PCR examination of the comF-flgM transcript indicates that readthrough from comF into the flgM operon is dependent on ComK. ComK negatively controls the transcription of hag by stimulating the transcription of comF-flgM, thereby increasing the production of the FlgM antisigma factor that inhibits sigmaD activity. There likely exists another comK-independent mechanism of hag transcription that requires mecA and possibly affects the sigmaD concentration in cells undergoing competence development.

Bacillus subtilis↗
PubMed1998

Altered srf expression in Bacillus subtilis resulting from changes in culture pH is dependent on the Spo0K oligopeptide permease and the ComQX system of extracellular control.

The expression of the srf operon of Bacillus subtilis, encoding surfactin synthetase and the competence regulatory protein ComS, was observed to be reduced when cells were grown in a rich glucose- and glutamine-containing medium in which late-growth culture pH was 5.0 or lower. The production of the surfactin synthetase subunits and of surfactin itself was also reduced. Raising the pH to near neutrality resulted in dramatic increases in srf expression and surfactin production. This apparent pH-dependent induction of srf expression required spo0K, which encodes the oligopeptide permease that functions in cell-density-dependent control of sporulation and competence, but not CSF, the competence-inducing pheromone that regulates srf expression in a Spo0K-dependent manner. Both ComP and ComA, the two-component regulatory pair that stimulates cell-density-dependent srf transcription, were required for optimal expression of srf at low and high pHs, but ComP was not required for pH-dependent srf induction. The known negative regulators of srf, RapC and CodY, were found not to function significantly in pH-dependent srf expression. Late-growth culture supernatants at low pH were not active in inducing srf expression in cells of low-density cultures but were rendered active when their pH was raised to near neutrality. ComQ (and very likely the srf-inducing pheromone ComX) and Spo0K were found to be required for the extracellular induction of srf-lacZ at neutral pH. The results suggest that srf expression, in response to changes in culture pH, requires Spo0K and another, as yet unidentified, extracellular factor. The study also provides evidence consistent with the hypothesis that ComP acts both positively and negatively in the regulation of ComA and that both activities are controlled by the ComX pheromone.

Bacillus subtilis↗