Purification, subunit structure and properties of two repressible phosphohydrolases of Bacillus subtilis

Potential Impact of Targeted HIV Pre-Exposure Prophylaxis Uptake Among Male Sex Workers

Little is known about the potential population-level impact of HIV pre-exposure prophylaxis (PrEP) use among cisgender male sex workers (MSWs), a high-risk subset of cisgender men who have sex with men (MSM). Using an agent-based model, we simulated HIV transmission among cisgender MSM in Rhode Island to determine the impacts of PrEP implementation where cisgender MSWs were equally ("standard expansion") or five times as likely ("focused expansion") to initiate PrEP compared to other cisgender MSM. Without PrEP, the model predicted 920 new HIV infections over a decade, or an average incidence of 0.39 per 100 person-years. In a focused expansion scenario where 15% of at-risk cisgender MSM used PrEP, the total number of new HIV infections was reduced by 58.1% at a cost of $57,180 per quality-adjusted life-year (QALY) gained. Focused expansion of PrEP use among cisgender MSWs may be an efficient and cost-effective strategy for reducing HIV incidence in the broader population of cisgender MSM.

PhoR/PhoP two component regulatory system affects biocontrol capability of Bacillus subtilis NCD-2

The Bacillus subtilis strain NCD-2 is an important biocontrol agent against cotton verticillium wilt and cotton sore shin in the field, which are caused by Verticillium dahliae Kleb and Rhizoctonia solani Kuhn, respectively. A mutant of strain NCD-2, designated M216, with decreased antagonism to V. dahliae and R. solani, was selected by mini-Tn10 mutagenesis and in vitro virulence screening. The inserted gene in the mutant was cloned and identified as the phoR gene, which encodes a sensor kinase in the PhoP/PhoR two-component system. Compared to the wild-type strain, the APase activities of the mutant was decreased significantly when cultured in low phosphate medium, but no obvious difference was observed when cultured in high phosphate medium. The mutant also grew more slowly on organic phosphate agar and lost its phosphatidylcholine-solubilizing ability. The suppression of cotton seedling damping-off in vivo and colonization of the rhizosphere of cotton also decreased in the mutant strain when compared with the wild type strain. All of these characteristics could be partially restored by complementation of the phoR gene in the M216 mutant.

Primary structure of cold-adapted alkaline phosphatase from a Vibrio sp. as deduced from the nucleotide gene sequence

Alkaline phosphatases (AP) are widely distributed in nature, and generally have a dimeric structure. However, there are indications that either monomeric or multimeric bacterial forms may exist. This paper describes the gene sequence of a psychrophilic marine Vibrio AP, previously shown to be particularly heat labile. The kinetic properties were also indicative of cold adaptation. The amino acid sequence of the Vibrio G15-21 AP reveals that the residues involved in the catalytic mechanism, including those ligating the metal ions, have precedence in other characterized APs. Compared with Escherichia coli AP, the two zinc binding sites are identical, whereas the metal binding site, normally occupied by magnesium, is not. Asp-153 and Lys-328 of E. coli AP are His-153 and Trp-328 in Vibrio AP. Two additional stretches of amino acids not present in E. coli AP are found inserted close to the active site of the Vibrio AP. The smaller insert could be accommodated within a dimeric structure, assuming a tertiary structure similar to E. coli AP. In contrast the longer insert would most likely protrude into the interface area, thus preventing dimer formation. This is the first primary structure of a putative monomeric AP, with indications as to the basis for a monomeric existence. Proximity of the large insert loop to the active site may indicate a surrogate role for the second monomer, and may also shape the catalytic as well as stability characteristics of this enzyme.

Sites internal to the coding regions of phoA and pstS bind PhoP and are required for full promoter activity

Bacillus subtilis PhoP and PhoR, a pair of two-component regulatory proteins, regulate the phosphate starvation response. Here, we used two other pho regulon promoters, the phoA and pstS promoters, to examine the mechanism of PhoP-specific activation of its target promoters. Both gel shift and DNase I footprinting assays indicate that PhoP bound to the two promoters. Unphosphorylated PhoP bound only to the multiple TTAACA-like sequences upstream of these two promoters, while phosphorylated PhoP extended the binding region in both the 5' and the 3' direction and, additionally, protected sequences internal to the coding region of these two genes. The PhoP binding sites in the coding region were necessary for full induction from either promoter during phosphate starvation. Deletion of these sites eliminated approximately 75% and 45% of the induced promoter activity of the phoA and pstS promoters respectively. In vitro transcription assays using the phoA promoters with various 3' ends confirmed the requirement of the PhoP-P binding to the coding region for full promoter activity. The multiple TTAACA-like sequences in the phoA and pstS promoters were essential for promoter activity, and deletion of one or more of these sequences in either promoter eliminated the promoter activity. Two pairs of TTAACA-like sequences were required for efficient PhoP binding and were suggested to be one B. subtilis Pho box. Based on our data, we have proposed a model for activation of the phoA and the pstS promoter by PhoP.

Influence of Bacillus subtilis phoR on cell wall anionic polymers

In Bacillus subtilis the Pho regulon is controlled by a sensor and regulator protein pair, PhoR and PhoP, that respond to phosphate concentrations. To facilitate studies of the Pho regulon, a strain with an altered PhoR protein was isolated by in vitro mutagenesis. The mutation in this strain (phoR12) leads to the production of a PhoR sensor kinase that, unlike the wild-type, is functionally active in phosphate-replete conditions. The lesion in PhoR12 was shown to be a single base change that results in an Arg to Ser substitution in a region of PhoR that is highly conserved in histidine sensor kinases. While a phoR-negative mutant was unable to induce the synthesis of cell wall teichuronic acid under phosphate-limited conditions, the phoR12 mutant showed a relative increase in teichuronic acid and a decrease in teichoic acid, even under phosphate-replete conditions. The latter suggests that some or all of the genes required for teichuronic acid synthesis are members of the Pho regulon.

Separate promoters direct expression of phoAIII, a member of the Bacillus subtilis alkaline phosphatase multigene family, during phosphate starvation and sporulation

Alkaline phosphatase (APase) expression can be induced in Bacillus subtilis by phosphate starvation or by sporulation. We have recently shown that there are multiple APase structural genes contributing to the total alkaline phosphatase expression in B. subtilis. The expression of the alkaline phosphatase III gene (phoAIII) was analysed under both phosphate-starvation induction and sporulation induction conditions. phoAII is transcribed from two promoter regions, PV and PS. The PV promoter initiated transcription 37 bp before the translation initiation codon and was used to transcribe phoAIII during phosphate-starvation induction in vegetative cells. The PS promoter initiated transcription 119 bp before the translation initiation codon and was used during sporulation induction. Genes which have previously been shown to affect total vegatative APase, pho regulon genes phoP, phoR and phoS, affected expression of phoAIII during phosphate starvation. Genes known to affect expression of total sporulation APase, i.e. spoIIA, spoIIG and spoIIE, affected phoAIII expression during sporulation induction. Our data show that one member of the APase multigene family, phoAIII, contributes to the total APase expression both during phosphate-starvation induction and sporulation induction, and that the mechanism of regulation includes two promoters, each requiring different regulatory genes.

Purification and properties of two membrane alkaline phosphatases from Bacillus subtilis 168

Two alkaline phosphatases were extracted from the membranes of Bacillus subtilis 168 stationary-phase cells and purified as homogeneous proteins by hydroxyapatite column chromatography. Alkaline phosphatases I and II differed in several properties such as subunit molecular weight, substrate specificity, thermostability, Km, pH stability, and peptide maps.

The Bacillus subtilis phoAIV gene: effects of in vitro inactivation on total alkaline phosphatase production

A degenerative oligodeoxyribonucleotide probe deduced from the first 19 amino acids of the mature alkaline phosphatase IV (APase IV) protein was used to clone a DNA fragment internal to the coding region of the phoAIV gene of Bacillus subtilis. An insertional mutation was constructed in the phoAIV locus using the integrative plasmid, pJM103, containing the cloned DNA fragment. The strain with the interrupted phoAIV gene showed no detectable APase IV product on Western-blot analysis. The impact of the phoAIV interruption on total APase production in B. subtilis 168 was analyzed under both phosphate starvation and sporulation culturing conditions. The mutation in phoAIV reduced total APase-specific activity by 75% in phosphate-starved cells, and resulted in the elimination of a salt-extractable membrane APase, as well as the secreted APase IV. Analysis of this membrane APase indicated that it is a phoAIV gene product which is localized within the membrane fraction of the lysed cell and not secreted. There was no effect on the production of sporulation APase. The phoAIV::pJM103 insertion was mapped and determined to be located at approx. 73 degrees on the B. subtilis 360 degrees chromosome.

Evidence for two structural genes for alkaline phosphatase in Bacillus subtilis

Two secreted alkaline phosphatase proteins were purified from cultures of Bacillus subtilis JH646MS. The two proteins showed slight differences in subunit molecular weight, substrate specificity, and charge characteristics. A total of 62% of the first 22 amino-terminal amino acids were identical. Both sequences showed conservation of structural features identified in Escherichia coli and human alkaline phosphatases. One alkaline phosphatase was a monomer and the other was a dimer. Southern analysis of genomic DNA with degenerative oligomers based on the amino acid sequences suggest that there are two structural genes for alkaline phosphatase in the genome of B. subtilis.

Apparent phosphate retrieval system in Bacillus cereus

Bacillus cereus secretes three different phospholipases C. We studied the effect of Pi levels in the growth medium on the production of these exoenzymes. Production of both phosphatidylcholine-preferring phospholipase C and sphingomyelinase C was repressed by Pi in the growth medium, whereas production of phosphatidylinositol phospholipase C was unaffected. We also found that B. cereus secretes a phosphate-repressed alkaline phosphatase activity. Together with a previously reported highly efficient, active uptake system for Pi, these three phosphate-repressed exoenzyme activities seem to be part of a phosphate retrieval mechanism that operates under growth-limiting concentrations of Pi. In natural soil systems, which are the natural habitats of B. cereus, the scarcity of Pi is the major growth-limiting factor. A phosphate-repressed metalloprotease activity was also detected in culture supernatants of B. cereus. It is unclear whether this exoenzyme activity also participates in the proposed phosphate-scavenging system.

Critical roles of spo0A and spo0H in vegetative alkaline phosphatase production in Bacillus subtilis

Growth conditions established to optimize vegetative alkaline phosphatase production and stability in Bacillus subtilis were used to compare alkaline phosphatase synthesis and secretion in isogenic strains JH646 (spo0A12) and JH646MS (spo0A12 abrB15). A mutation in spo0A blocked vegetative alkaline phosphatase production, and a second mutation at the abrB locus resulted in hyperinduction of vegetative alkaline phosphatase. Phosphate regulation of vegetative alkaline phosphatase synthesis was unaffected in the double mutant. spo0H, on a multicopy plasmid, partially overcame the spo0A effect.

Cloning and nucleotide sequence of phoP, the regulatory gene for alkaline phosphatase and phosphodiesterase in Bacillus subtilis

Two DNA fragments which complement the alkaline phosphatase-negative mutation phoP of Bacillus subtilis were cloned from a B. subtilis chromosome with the prophage vector phi CM (a derivative of phi 105). One of the fragments contained the regulatory gene phoR in addition to phoP. Nucleotide sequence analysis of the phoP region revealed that the phoP gene product consists of 241-amino-acid residues and that the sequence of these amino acids is extensively homologous with the sequence of the phoB gene product. This protein is the positive regulator for the phosphate regulon in Escherichia coli. It therefore appears that phoP is a regulatory gene for alkaline phosphatase synthesis in B. subtilis.

A novel glycerophosphodiesterase from Bacillus pumilus

A novel glycerophosphodiesterase activity was detected in extracts from phosphate-starved Bacillus pumilus DSM27 cells. The enzyme had a substrate specificity for glycerophosphodiester bonds and the reaction product formed with partially purified enzyme was (sn)-glycero-3-phosphate. Purified cell wall teichoic acid of the polyglycerophosphate type, as well as deacylated, unsubstituted lipoteichoic acid of the polyglycerophosphate type, di(glycerophospho)glycerol (deacylated cardiolipin) and mono(glycerophospho)glycerol (deacylated phosphatidylglycerol) served as substrates for the enzyme. Their native counterparts, however, cell wall-bound polyglycerophosphate, lipoteichoic acid (D-alanine substituted and dealanylated), cardiolipin and phosphatidylglycerol were poor or no substrates, respectively. Enzyme activity was inhibited by purified cell walls and by heparin. The enzyme was partially purified using a column of Heparin-Sepharose.

Teichoicase from Bacillus subtilis Marburg

The properties of a teichoic acid degrading enzyme (teichoicase) isolated from Bacillus subtilis Marburg are described. The purified enzyme showed phosphodiesterase activity but not phosphomonoesterase activity, and it had an absolute substrate specificity for alpha-glucosylated glycerol teichoic acid, the endogenous cell wall teichoic acid of the enzyme-producing cell. The substrate was degraded by an exo-mechanism yielding the monomer alpha-D-glucose 1 leads to 2 (sn)glycero-3-phosphate. When B. subtilis Marburg was grown in a rich medium, enzyme activity was detected in extracts from sporulating cells. Teichoicase activity was present in a mutant blocked in stage II of the sporulation process but was absent in a mutant blocked in stage O. It was concluded that teichoicase is active on enzyme-producing cells since the reaction product could be detected in their culture supernatant. Attempts to demonstrate analogous enzyme activity in other Bacillus strains failed. The enzyme could be used for the rapid detection of alpha-glucosylated glycerol teichoic acid and for the controlled alteration of native bacterial cell surfaces exhibiting the appropriate structure.

Alkaline phosphatase secretion-negative mutant of Bacillus licheniformis 749/C

An alkaline phosphatase secretion-blocked mutant of Bacillus licheniformis 749/C was isolated. This mutant had defects in the phoP and phoR regions of the chromosome. The selection procedure was based on the rationale that N-methyl-N'-nitro-N-nitrosoguanidine can induce mutations of closely linked multiple genes. The malate gene and the phoP and phoR genes are located at the 260-min position in the Bacillus subtilis chromosome; hence, the malate gene could be used as a marker for the mutation of the phoP and phoR regions of the chromosome. In a two-step selection procedure, strains defective in malate utilization were first selected with the cephalosporin C procedure. Second, these malate-defective strains were further screened in a dye medium to select strains with defects in alkaline phosphatase secretion. One stable mutant (B. licheniformis 749/cNM 105) had a total secretion block for alkaline phosphatase and had the following additional characteristics: (i) the amount of alkaline phosphatase synthesized was comparable to that in the wild type; (ii) the alkaline phosphatase was membrane bound; (iii) the mutant strain alkaline phosphatase, in contrast to that of the wild type, could not be extracted with MgCl2, although the amounts of protein extracted from each strain were comparable; (iv) the sodium dodecyl sulfate-polyacrylamide gel pattern of MgCl2-extracted proteins from the mutant strain was different from that of the wild-type proteins; (v) the mutant, unlike the wild type, could not use malate as a sole source of carbon; and (vi) the outside surface of the wall of the mutant cells contained an additional electron-dense layer that was not present on the wild-type cell wall surface.

Cell wall teichoic acid as a reserve phosphate source in Bacillus subtilis

Although exponential growth of Bacillus subtilis 168 in a phosphate-limited medium halted with the exhaustion of inorganic phosphate, the bacteria continued to grow at a slower rate for a further 3 to 4 h at 37 degrees C. This postexponential growth in the absence of an exogenous phosphate supply was accompanied by a loss of teichoic acid from the cell walls of the bacteria. Quantitative analysis of walls and culture fluids showed that the phosphate loss from the walls could not be accounted for by an increase in phosphate-containing compounds in the medium, which implied that the cells were using their own wall teichoic acids to supply phosphate necessary for growth. Addition of exogenous teichoic acid to phosphate-starved cultures resulted in stimulation of growth and in the simultaneous disappearance of teichoic acid phosphate from the medium. It is proposed that teichoic acids, which can contain more than 30% of the total phosphorus of exponential-phase cells, can be used as a reserve phosphate source when the bacteria are starved for inorganic phosphate.

Alkaline phosphatase possessing alkaline phosphodiesterase activity and other phosphodiesterases in Bacillus subtilis

In Bacillus subtilis Marburg strain, single-point mutations in the phoP locus brought about simultaneous losses of the major activities of alkaline phosphatase (APase) and alkaline phosphodiesterase (APDase). Revertants recovered the two activities. APases with APDase activity were purified from the membrane fraction of B. subtilis 6160-BC6 and from the culture fluid of an APase-secreting B. subtilis mutant strain, RAN 1. In addition to these major APases with APDase activity, at least two kinds of phosphodiesterase (PDase) without phosphatase activity were found in the cytoplasmic supernatants of RAN 1 and an APase-less B. subtilis mutant strain, SP25. Another minor APase with a molecular weight of about 80,000, which had almost no PDase activity, was isolated from the membrane fraction of strain 6160-BC6. Enzyme distribution in subcellular fractions from various strains cultured in high- and low-phosphate media was analyzed. The PDases did not cross-react with rabbit antiserum against the RAN 1 APase with APDase activity. The main component of the PDases had a molecular weight of about 80,000 and was most active at pH 8.0. These results suggest that APase with APDase activity is different from PDases detected in cytoplasmic supernatants and that phoP is the structural gene for the phosphate-repressible APase with APDase activity.

Purification and characterization of extracellular soluble and membrane-bound insoluble alkaline phosphatases possessing phosphodiesterase activities in Bacillus subtilis

A membrane-bound insoluble alkaline phosphatase (APase) and an extracellular soluble APase were purified, respectively, from a membrane preparation of Bacillus subtilis 6160-BC6, which carries a mutation to produce APase constitutively, and from a culture fluid of a mutant strain. RAN 1, isolated from strain 6160-BC6, which produces an extracellular soluble APase. The two preparations were homogeneous, as judged by sodium dodecyl sulfate discontinuous gel electrophoresis and by gel electrophoreses in the presence of 8 M urea at pH 9.3 and 4.3. RAN 1 APase was crystallized. Both preparations possessed phosphatase and phosphodiesterase activities, and their pH optima were both at 9.5. They were competitively inhibited by phosphate or arsenate and were activated by the addition of Ca2+ but not by Zn2+. The APase and alkaline phosphodiesterase activities seemed to be contained in the same protein molecule. The molecular weight of 6160-BC6 APase was estimated to be 46,000 +/- 1,000, and that of RAN 1 APase was estimated to be 45,000 +/- 1,000. The largest difference between the 6160-BC6 and RAN 1 APase's was in solubility in low-ionic-strength solutions. Present results suggest that each enzyme is composed of a single polypeptide chain and that 6160-BC6 APase aggregates in solutions of low ionic strength.

Genetic control of the glp system in Bacillus subtilis

In pleiotropic negative glycerol utilization mutants (GlpPI mutants) of Bacillus subitilis, glycerol kinase and sn-glycerol 3-phosphate (G3P) dehydrogenase are noninducible. GlpPI mutants also fail to take up exogenous [14C]G3P. To study the regulation of the glp system in B. subtilis phenotypically, Glp+ revertants were isolated from GlpPI mutants. Four classes of revertants were identified: phenotypically, wild type; R1 type, which contains an informational suppressor, R2 type, which produced G3P dehydrogenase constitutively; and R3 type, with a temperature-sensitive Glp phenotype producing G3P dehydrogenase constitutively at permissive temperature (32 degrees C). The properties of the revertants indicate that the glpPI locus codes for a protein with a positive regulatory function.

Repression of sporulation in Bacillus subtilis by L-malate

L-Malate repressed sporulation in the wild-type strain of Bacillus subtilis. When 75 mM L-malate was added to the growth medium at the time of inoculation, the appearance of heat-resistant spores was delayed 6 to 8 h. The synthesis of extracellular serine protease, alkaline phosphatase, glucose dehydrogenase, and dipicolinic acid was similarly delayed. Sporulation was not repressed when malate was added to the culture at t4 or later. A mutant was selected for ability to sporulate in the presence of malate. This strain could also sporulate in the presence of glucose. The malate-resistant mutant grew poorly with malate as sole carbon source, although it possessed an intact citric acid cycle, and it showed increased levels of malic enzyme. This indicates a defect in the metabolism of malate in the mutant. A mutant lacking malate dehydrogenase activity was also able to sporulate in the presence of malate. A model for the regulation of sporulation by malate is presented and discussed. Citric acid cycle intermediates other than malate did not affect sporulation. In contrast to previous results, sporulation of certain citric acid cycle mutants could be greatly increased or completely restored by the addition of intermediates after the enzymatic block. The results indicate that the failure of citric acid cycle mutants to sporulate can be adequately explained by lack of energy and lack of glutamate.