Possible involvement of bacterial autolytic enzymes in flagellar morphogenesis

Identification of Genes Required for Swarming Motility in Bacillus subtilis Using Transposon Mutagenesis and High-Throughput Sequencing (TnSeq)

Bacillus subtilis exhibits swarming motility, a flagellar-mediated form of surface motility. Here, we use transposon mutagenesis and sequencing (TnSeq) to perform a high-throughput screen for candidate genes required for swarming. The TnSeq approach identified all of the known genes required for flagellar biosynthesis and nearly all of the previously reported regulators that promote swarming. Moreover, we identified an additional 36 genes that improve swarming and validated them individually. Among these, two mutants with severe defects were recovered, including fliT, required for flagellar biosynthesis, and a gene of unknown function, yolB, whose defect could not be attributed to a lack of flagella. In addition to discovering additional genes required for B. subtilis swarming, our work validates TnSeq as a powerful approach for comprehensively identifying genes important for nonessential processes such as colony expansion on plates. IMPORTANCE In TnSeq, transposons are randomly inserted throughout the chromosome at a population level, but insertions that disrupt genes of essential function cause strains that carry them to fall out of the population and appear underrepresented at the sequence level. Here, we apply TnSeq to the nonessential phenotype of motility in B. subtilis and spatially select for cells proficient in swarming. We find that insertions in nearly all genes previously identified as required for swarming are underrepresented in TnSeq analysis, and we identify 36 additional genes that enhance swarming. We demonstrate that TnSeq is a powerful tool for the genetic analysis of motility and likely other nonlethal screens for which enrichment is strong.

CwlQ Is Required for Swarming Motility but Not Flagellar Assembly in Bacillus subtilis

Lytic enzymes play an essential role in the remodeling of bacterial peptidoglycan (PG), an extracellular mesh-like structure that retains the membrane in the context of high internal osmotic pressure. Peptidoglycan must be unfailingly stable to preserve cell integrity, but must also be dynamically remodeled for the cell to grow, divide, and insert macromolecular machines. The flagellum is one such macromolecular machine that transits the PG, and flagellar insertion is aided by localized activity of a dedicated PG lyase in Gram-negative bacteria. To date, there is no known dedicated lyase in Gram-positive bacteria for the insertion of flagella. Here, we take a reverse-genetic candidate-gene approach and find that cells mutated for the lytic transglycosylase CwlQ exhibit a severe defect in flagellum-dependent swarming motility. We further show that CwlQ is expressed by the motility sigma factor SigD and is secreted by the type III secretion system housed inside the flagellum. Nonetheless, cells with mutations of CwlQ remain proficient for flagellar biosynthesis even when mutated in combination with four other lyases related to motility (LytC, LytD, LytF, and CwlO). The PG lyase (or lyases) essential for flagellar synthesis in B. subtilis, if any, remains unknown.IMPORTANCE Bacteria are surrounded by a wall of peptidoglycan and early work in Bacillus subtilis was the first to suggest that bacteria needed to enzymatically remodel the wall to permit insertion of the flagellum. No PG remodeling enzyme alone or in combination, however, has been found to be essential for flagellar assembly in B. subtilis Here, we take a reverse-genetic candidate-gene approach and find that the PG lytic transglycosylase CwlQ is required for swarming motility. Subsequent characterization determined that while CwlQ was coexpressed with motility genes and is secreted by the flagellar secretion apparatus, it was not required for flagellar synthesis. The PG lyase needed for flagellar assembly in B. subtilis remains unknown.

Prodigiosin Induces Autolysins in Actively Grown Bacillus subtilis Cells

Prodigiosin produced by marine bacterium Vibrio ruber DSM 14379 exhibits a potent antimicrobial activity against a broad range of Gram positive and Gram negative bacteria. The mechanism of prodigiosin antimicrobial action, however, is not known. In this work, the effect of prodigiosin on Bacillus subtilis growth, cell membrane leakage, and induction of autolysins was studied. Treating B. subtilis with prodigiosin resulted in rapid decline of optical density and increased cell membrane leakage measured by β-galactosidase activity. Cell lysis was initiated immediately after treatment with prodigiosin in the middle exponential phase and was completed within 2 h. Lytic activity of prodigiosin in mutant strains with impaired autolysin genes lytABCD decreased for 80% compared to the wild type strain, while in lytABCDEF mutant strain prodigiosin had no bacteriolytic but only bacteriostatic effect. Fast prodigiosin lytic activity on individual B. subtilis cells was confirmed by a modified comet assay. The results indicate that prodigiosin autolysin induction in B. subtilis is growth phase dependent.

The structure and regulation of flagella in Bacillus subtilis

Bacterial flagellar motility is among the most extensively studied physiological systems in biology, but most research has been restricted to using the highly similar Gram-negative species Escherichia coli and Salmonella enterica. Here, we review the recent advances in the study of flagellar structure and regulation of the distantly related and genetically tractable Gram-positive bacterium Bacillus subtilis. B. subtilis has a thicker layer of peptidoglycan and lacks the outer membrane of the Gram-negative bacteria; thus, not only phylogenetic separation but also differences in fundamental cell architecture contribute to deviations in flagellar structure and regulation. We speculate that a large number of flagella and the absence of a periplasm make B. subtilis a premier organism for the study of the earliest events in flagellar morphogenesis and the type III secretion system. Furthermore, B. subtilis has been instrumental in the study of heterogeneous gene transcription in subpopulations and of flagellar regulation at the translational and functional level.

Peptidoglycan maturation enzymes affect flagellar functionality in bacteria

The flagellar machinery is a highly complex organelle composed of a free rotating flagellum and a fixed stator that converts energy into movement. The assembly of the flagella and the stator requires interactions with the peptidoglycan layer through which the organelle has to pass for externalization. Lytic transglycosylases are peptidoglycan degrading enzymes that cleave the sugar backbone of peptidoglycan layer. We show that an endogenous lytic transglycosylase is required for full motility of Helicobacter pylori and colonization of the gastric mucosa. Deficiency of motility resulted from a paralysed phenotype implying an altered ability to generate flagellar rotation. Similarly, another Gram-negative pathogen Salmonella typhimurium and the Gram-positive pathogen Listeria monocytogenes required the activity of lytic transglycosylases, Slt or MltC, and a glucosaminidase (Auto), respectively, for full motility. Furthermore, we show that in absence of the appropriate lytic transglycosylase, the flagellar motor protein MotB from H. pylori does not localize properly to the bacterial pole. We present a new model involving the maturation of the surrounding peptidoglycan for the proper anchoring and functionality of the flagellar motor.

Role of the sigmaD-dependent autolysins in Bacillus subtilis population heterogeneity

Exponentially growing populations of Bacillus subtilis contain two morphologically and functionally distinct cell types: motile individuals and nonmotile multicellular chains. Motility differentiation arises because RNA polymerase and the alternative sigma factor sigma(D) activate expression of flagellin in a subpopulation of cells. Here we demonstrate that the peptidoglycan-remodeling autolysins under sigma(D) control, LytC, LytD, and LytF, are expressed in the same subpopulation of cells that complete flagellar synthesis. Morphological heterogeneity is explained by the expression of LytF that is necessary and sufficient for cell separation. Moreover, LytC is required for motility but not at the level of cell separation or flagellum biosynthesis. Rather, LytC appears to be important for flagellar function, and motility was restored to a LytC mutant by mutation of either lonA, encoding the LonA protease, or a gene encoding a previously unannotated swarming motility inhibitor, SmiA. We conclude that heterogeneous activation of sigma(D)-dependent gene expression is sufficient to explain both the morphological heterogeneity and functional heterogeneity present in vegetative B. subtilis populations.

The flagellar muramidase from the photosynthetic bacterium Rhodobacter sphaeroides

We have characterized open reading frame RSP0072, which is located within the flgG operon in Rhodobacter sphaeroides. The amino acid sequence analysis of this gene product showed the presence of a soluble lytic transglycosylase domain. The deletion of the N-terminal region (90 amino acids) of the product of RSP0072 yields a leaky nonmotile phenotype, as determined by swarm assays in soft agar. Electron micrographs revealed the lack of flagella in mutant cells. The purified wild-type protein showed lytic activity on extracts of Micrococcus luteus. In contrast, no lytic activity was observed when the residues E57 or E83 were replaced by alanine. Affinity blotting suggests that the protein encoded by RSP0072 interacts with the flagellar rod-scaffolding protein FlgJ, which lacks the muramidase domain present in FlgJ of many bacteria. We propose that the product of RSP0072 is a flagellar muramidase that is exported to the periplasm via the Sec pathway, where it interacts with FlgJ to open a gap in the peptidoglycan layer for the subsequent penetration of the nascent flagellar structure.

Cell population heterogeneity during growth of Bacillus subtilis

We have discovered that cells of Bacillus subtilis at the mid-exponential phase of growth are a mixed population of two strikingly different cell types. One type is single swimming cells (or cell doublets) in which the transcription factor for motility, sigma(D), is active (sigma(D) ON). The other type is long chains of sessile cells in which sigma(D) is inactive (sigma(D) OFF). The population is strongly biased toward sigma(D)-ON cells by the action of a novel regulatory protein called SwrA. SwrA stimulates the transcription of a large operon (the flagellum/chemotaxis operon), which includes the genes for sigma(D) and an activator of sigma(D)-directed gene expression, SwrB. Cell population heterogeneity could enable B. subtilis to exploit its present location through the production of sessile cells as well as to explore new environmental niches through the generation of nomadic cells.

A master regulator for biofilm formation by Bacillus subtilis

Wild strains of Bacillus subtilis are capable of forming architecturally complex communities of cells known as biofilms. Critical to biofilm formation is the eps operon, which is believed to be responsible for the biosynthesis of an exopolysaccharide that binds chains of cells together in bundles. We report that transcription of eps is under the negative regulation of SinR, a repressor that was found to bind to multiple sites in the regulatory region of the operon. Mutations in sinR bypassed the requirement in biofilm formation of two genes of unknown function, ylbF and ymcA, and sinI, which is known to encode an antagonist of SinR. We propose that these genes are members of a pathway that is responsible for counteracting SinR-mediated repression. We further propose that SinR is a master regulator that governs the transition between a planktonic state in which the bacteria swim as single cells in liquid or swarm in small groups over surfaces, and a sessile state in which the bacteria adhere to each other to form bundled chains and assemble into multicellular communities.

The Staphylococcus aureus cidAB operon: evaluation of its role in regulation of murein hydrolase activity and penicillin tolerance

Recent studies have shown that expression of the Staphylococcus aureus lrgAB operon inhibits murein hydrolase activity and decreases sensitivity to penicillin-induced killing. It was proposed that the lrgAB gene products function in a manner analogous to an antiholin, inhibiting a putative holin from transporting murein hydrolases out of the cell. In the present study the cidAB operon was identified and characterized based on the similarity of the cidA and cidB gene products to the products of the lrgAB operon. Zymographic and quantitative analyses of murein hydrolase activity revealed that mutation of the cidA gene results in decreased extracellular murein hydrolase activity compared to that of S. aureus RN6390, the parental strain. Complementation of cidA expression restored the wild-type phenotype, indicating that expression of the cidAB operon has a positive influence on extracellular murein hydrolase activity. The cidA mutant also displayed a significant decrease in sensitivity to the killing effects of penicillin. However, complementation of the cidA defect did not restore penicillin sensitivity to wild-type levels. Reverse transcriptase PCR also revealed that cidAB is maximally expressed during early exponential growth, opposite of what was previously observed for lrgAB expression. Based on these results, we propose that the cidAB operon encodes the holin-like counterpart of the lrgAB operon and acts in a manner opposite from that of lrgAB by increasing extracellular murein hydrolase activity and increasing sensitivity to penicillin-induced killing.

Characterization of a new sigma-K-dependent peptidoglycan hydrolase gene that plays a role in Bacillus subtilis mother cell lysis

Bacillus subtilis produces a 30-kDa peptidoglycan hydrolase, CwlH, during the late sporulation phase. Disruption of yqeE led to a complete loss of CwlH formation, indicating the identity of yqeE with cwlH. Northern blot analysis of cwlH revealed a 0.8-kb transcript after 6 to 7.5 h for the wild-type strain but not for the sigma(F), sigma(E), sigma(G), and sigma(K) mutants. Expression of the sigma(K)-dependent cwlH gene depended on gerE. Primer extension analysis also suggested that cwlH is transcribed by Esigma(K) RNA polymerase. CwlH produced in Escherichia coli harboring a cwlH plasmid is an N-acetylmuramoyl-L-alanine amidase (EC 3.5.1.28) and exhibited an optimum pH of 7.0 and high-level binding to the B. subtilis cell wall. A cwlC cwlH double mutation led to a lack of mother cell lysis even after 7 days of incubation in DSM medium, but the single mutations led to mother cell lysis after 24 h.

Peptidoglycan-hydrolyzing activity of the FlgJ protein, essential for flagellar rod formation in Salmonella typhimurium

Because the rod structure of the flagellar basal body crosses the inner membrane, the periplasmic space, and the outer membrane, its formation must involve hydrolysis of the peptidoglycan layer. So far, more than 10 genes have been shown to be required for rod formation in Salmonella typhimurium. Some of them encode the component proteins of the rod structure, and most of the remaining genes are believed to encode proteins involved in the export process of the component proteins. Although FlgJ has also been known to be involved in rod formation, its exact role has not been understood. Recently, it was suggested that the C-terminal half of the FlgJ protein has homology to the active center of some muramidase enzymes from gram-positive bacteria. In this study, we showed that the purified FlgJ protein from S. typhimurium has a peptidoglycan-hydrolyzing activity and that this activity is localized in its C-terminal half. Through oligonucleotide-directed mutagenesis, we constructed flgJ mutants with amino acid substitutions in the putative active center of the muramidase. The resulting mutants produced FlgJ proteins with reduced enzymatic activity and showed poor motility. These results indicate that the muramidase activity of FlgJ is essential for flagellar formation. Immunoblotting analysis with the fractionated cell extracts revealed that FlgJ is exported to the periplasmic space, where the peptidoglycan layer is localized. On the basis of these results, we conclude that FlgJ is the flagellum-specific muramidase which hydrolyzes the peptidoglycan layer to assemble the rod structure in the periplasmic space.

Regulation of a new cell wall hydrolase gene, cwlF, which affects cell separation in Bacillus subtilis

Bacillus subtilis produces a 35-kDa cell wall hydrolase, CwlF, during vegetative growth. The CwlF protein was extracted from B. subtilis cwlB sigD mutant cells and separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. N-terminal amino acid sequencing revealed that its sequence is completely identical to that of the internal region of the papQ gene product. Disruption of the papQ gene in the B. subtilis chromosome led to the complete loss of CwlF, indicating that papQ is identical to cwlF. CwlF exhibits high sequence similarity to the p60 proteins of Listeria species, NlpC proteins of Escherichia coli and Haemophilus influenzae, and Enp2 protein of Bacillus sphaericus. The beta-galactosidase activity of the cwlF-lacZ transcriptional fusion and Northern blot analysis of the cwlF gene indicated that the gene is expressed as a monocistronic operon during the exponential growth phase, and primer extension analysis suggested that the cwlF gene is transcribed mainly by EsigmaA RNA polymerase and weakly by EsigmaH RNA polymerase. While the cells of the cwlF-deficient mutant were about twice as long as those of the wild-type strain, the cwlF sigD double mutant cells exhibited extraordinary microfiber formation, in contrast to the filamentation of the sigD mutant. The CwlF production was not affected by the pleiotropic mutations flaD1 and degU32(Hy), which endow cells with the ability of extensive filamentation.

The role of autolysins during vegetative growth of Bacillus subtilis 168

A set of isogenic mutants of Bacillus subtilis 168, insertionally inactivated in the genes encoding a number of lytic enzymes and a sigma factor (sigma D, which controls the expression of a number of autolysins) was constructed. Phenotypic analysis of the mutants determined the individual and combined roles of the autolysins in vegetative growth. The major vegetative autolysins of B. subtilis, LytC (50 kDa amidase) and LytD (90 kDa glucosaminidase), were shown to have roles in cell separation, cell wall turnover, antibiotic-induced lysis and motility. LytC was also shown to have a role in general cell lysis induced by sodium azide. Renaturing SDS-PAGE of cell-wall-binding protein extracts of the mutant strains revealed the presence of a novel autolysin that was previously masked by LytC. This 49 kDa enzyme was shown to be sigma D-controlled and was identified as a candidate cell separation and cell wall turnover enzyme. A multiple mutant strain, lacking LytC, LytD and the 49 kDa enzyme, retained at least ten bands of autolytic activity. These may correspond to individual or proteolytically processed novel autolysins, the functions of which are unknown. The multiple mutant strains facilitate the study of these, and other lytic enzymes, to determine their cellular functions.

Characterisation of a Transposon-induced Pleiotropic Mutant ofClostridium acetobutylicumP262

Transposon-induced metronidazole resistance was used as a selection system for the isolation of Clostridium acetobutylicum P262 mutants with altered electron transport pathways. The metronidazole resistant transconjugant of interest, mutant 3R, displayed resistance to DNA damaging agents, UV and bleomycin, and harboured a single transposon insertion within a structural gene, designated sum(susceptibility to metronidazole). The sum gene encoded a 334 amino-acid protein, with 36% identity and 57-58% similarity at the amino acid level to two archaebacterial protein sequences which appear to represent a class of uncharacterised reductase enzymes. Physiological studies of mutant 3R revealed a number of pleiotropic characteristics which included enhanced autolysin activity, increased motility, impaired clostridial cell formation, and resistance to the toxic tripeptide analogue, bialaphos. The introduction of the sum gene in multiple copies on a plasmid vector into the related strain Clostridium beijerinckii NCIMB 8052, resulted in inhibition of cell division, motility and autolysin activity. The sum gene appears to be a member of a new subgroup of activases with reducing activity, which may control a regulon affecting different stationary phase processes such as clostridial differentiation and sporulation in C. acetobutylicum P262. The metronidazole resistant phenotype of the sum mutant can be attributed to an increased capacity for DNA repair.

Bacillus subtilis mutant deficient in the major autolytic amidase and glucosaminidase is impaired in motility

The purified autolytic endo-beta-N-acetylglucosaminidase of Bacillus subtilis AC327 was cleaved with cyanogen bromide, and the N-terminal amino acid sequence of one of the peptide fragments was determined. Then, a DNA fragment containing a part of the glucosaminidase gene was cloned into Escherichia coli JM109 using synthetic oligonucleotides as probes whose sequences had been deduced from the N-terminal amino acid sequence. Zymographic analysis showed that the resultant glucosaminidase-deficient strain lacked a 35-kDa lytic band in addition to a 90-kDa lytic one corresponding to the glucosaminidase. A double mutant strain deficient in the major two autolysins (amidase and glucosaminidase) exhibited greatly impaired motility on a swarm plate whereas the single mutant strains were motile.

Alternative sigma factors and the regulation of flagellar gene expression

Synthesis of bacterial flagella and the accompanying array of chemotaxis receptors and transducers represents a major commitment of energy and resources for a growing bacterial cell and is subject to numerous levels of regulation. Genes for flagellar and chemotaxis proteins are expressed in a complex transcriptional cascade. This regulatory hierarchy acts to ensure that the highly expressed filament structural protein, flagellin, is synthesized only after a prerequisite set of structural proteins has been expressed and properly assembled. Recent evidence suggests that many bacteria utilize an alternative sigma (sigma) subunit, similar in specificity to the Bacillus subtilis sigma 28 protein, to direct transcription of flagellin, chemotaxis and motility genes. In Caulobacter crescentus and Campylobacter spp., both a sigma 54-like factor and a sigma 28-like factor participate in the transcription of flagellar and chemotaxis genes. Conversely, a sigma 28-like factor controls non-motility functions in at least one non-flagellated organism.

Molecular cloning and sequencing of a major Bacillus subtilis autolysin gene

A major Bacillus subtilis 168S autolysin (N-acetylmuramoyl-L-alanine amidase [EC 3.5.1.28]) was purified and then cleaved with cyanogen bromide. The N-terminal amino acid sequence of one of the resultant peptides was determined in order to make synthetic oligonucleotides. A 2.5-kb EcoRI fragment was cloned into Escherichia coli JM109 and detected by colony hybridization by using the oligonucleotides as probes. Sequencing of the insert showed the presence of an open reading frame (designated cwlB), starting at a UUG codon, which encodes a polypeptide of 496 amino acids with a molecular mass of 52,623 Da. CWLB had a presumed signal peptide which is processed after Ala at position 24. Insertional inactivation of the cwlB gene of the B. subtilis chromosome led to an approximately 90% decrease in the total cell wall hydrolytic activity of stationary-phase cells and extraordinary resistance to cell lysis, even after 6 days of incubation at 37 degrees C. No apparent changes in cell morphology, motility, competence, sporulation, or germination were observed.

The bacterial flagellum and flagellar motor: structure, assembly and function

The bacterial flagellum is a complex multicomponent structure which serves as the propulsive organelle for many species of bacteria. Rotation of the helical flagellar filament, driven by a proton-powered motor embedded in the cell wall, enables the flagellum to function as a screw propeller. It seems likely that almost all of the genes required for flagellar formation and function have been identified. Continuing analysis of the portions of the genome containing these genes may reveal the existence of a few more. Transcription of the flagellar genes is under the control of the products of a single operon, and so these genes constitute a regulon. Other controls, both transcriptional and post-transcriptional, have been identified. Many of these genes have been sequenced, and the information obtained will aid in the design of experiments to clarify the various regulatory mechanisms of the flagellar regulon. The flagellum is composed of several substructures. The long helical filament is connected via the flexible hook to the complex basal body which is located in the cell wall. The filament is composed of many copies of a single protein, and can adopt a number of distinct helical forms. Structural analyses of the filament are adding to our understanding of this dynamic polymer. The component proteins of the hook and filament have all been identified. Continuing studies on the structure of the basal body have revealed the presence of several hitherto unknown basal-body proteins, whose identities and functions have yet to be elucidated. The proteins essential for energizing the motor, the Mot and switch proteins, are thought to exist as multisubunit complexes peripheral to the basal body. These complexes have yet to be identified biochemically or morphologically. Not surprisingly, flagellar assembly is a complex process, occurring in several stages. Assembly occurs in a proximal-to-distal fashion; the basal body is assembled before the hook, and the hook before the filament. This pattern is also maintained within the filament, with monomers added at the distal end of the polymer; the same is presumably true of the other axial components. An exception to this general pattern is assembly of the Mot proteins into the motor, which appears to be possible at any time during flagellar assembly. With the identification of the genes encoding many of the flagellar proteins, the roles of these proteins in assembly is understood, but the function of a number of gene products in flagellar formation remains unknown.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of aminoglycoside antibiotics on the autolytic enzyme of Streptomyces griseus

The isolated cell wall of Streptomyces griseus 52-1 strain labelled with fluorescein isothiocyanate (FITC) and containing wall-bound autolytic enzyme was lysed as a function of different cations. The autolysis was accelerated by aminoglycoside antibiotics (streptomycin and the structurally closely related neomycin) which have a polycationic character. Since this strain is a streptomycin producer it is suggested that streptomycin may have a regulatory function on autolysis.

Studies of sigma D-dependent functions in Bacillus subtilis

Gene expression in Bacillus subtilis can be controlled by alternative forms of RNA polymerase programmed by distinct sigma factors. One such factor, sigma D (sigma 28), is expressed during vegetative growth and has been implicated in the transcription of a regulon of genes expressed during exponential growth and the early stationary phase. We have studied several functions related to flagellar synthesis and chemotaxis in B. subtilis strains in which sigma D is missing or is present at reduced levels. Previous studies showed that a null mutant, which contains a disrupted copy of the sigma D structural gene (sigD), fails to synthesize flagellin and grows as long filaments. We now show that these defects are accompanied by the lack of synthesis of the methyl-accepting chemotaxis proteins and a substantial decrease in two autolysin activities implicated in cell separation. A strain containing an insertion upstream of the sigD gene that reduces the level of sigma D protein grew as short chains and was flagellated but was impaired in chemotaxis and/or motility. This reduced level of sigma D expression suggests that the sigD gene may be part of an operon. A strain containing an insertion downstream of the sigD gene expressed nearly wild-type levels of sigma D protein but was also impaired in chemotaxis and/or motility, suggesting that genes downstream of sigD may also be involved in these functions. Genetic experiments demonstrate that sigD is allelic to the flaB locus, which was initially isolated as a locus affecting flagellin expression (G. F. Grant and M. I. Simon, J. Bacteriol. 99:116-124, 1969).

Lysis and aberrant morphology of Bacillus subtilis cells caused by surfactants and their relation to autolysin activity

The surfactants tested in this study lysed Bacillus subtilis 168 cells at the logarithmic growth phase. Results obtained with inhibitors and a mutant that had defective autolytic enzymes suggested that cell lysis resulted from the deregulation of autolysin activity. The addition of surfactants at sublytic concentrations produced twisted cells, filamented cells, or both. Autolysins extracted with 5 M LiCl from the cell wall fraction and lysozyme added to cells that were treated with surfactants restored the apparently normal cell rod morphology, suggesting that surfactants interfere with the role of autolysins in normal construction of the cell envelope. The rates of cellular autolysis and autolysin activity remaining in growing cells after exposure to a surfactant at a sublytic concentration decreased, although the rate of turnover of cell wall peptidoglycan was the same as that of control cells. Surfactants were suggested to interact with the regulatory system of autolysins and, thus, to affect the activities of autolysins in B. subtilis cells and to cause either morphological changes or cell autolysis, depending on the concentration of surfactants.

Biochemical characterization of avirulent exoC mutants of Agrobacterium tumefaciens

The synthesis of periplasmic beta(1-2)glucan is required for crown gall tumor formation by Agrobacterium tumefaciens and for effective nodulation of alfalfa by Rhizobium meliloti. The exoC (pscA) gene is required for this synthesis by both bacteria as well as for the synthesis of capsular polysaccharide and normal lipopolysaccharide. We tested the possibility that the pleiotropic ExoC phenotype is due to a defect in the synthesis of an intermediate common to several polysaccharide biosynthetic pathways. Cytoplasmic extracts from wild-type A. tumefaciens and from exoC mutants of A. tumefaciens containing a cloned wild-type exoC gene synthesized in vitro UDP-glucose from glucose, glucose 1-phosphate, and glucose 6-phosphate. Extracts from exoC mutants synthesized UDP-glucose from glucose 1-phosphate but not from glucose or glucose 6-phosphate. Membranes from exoC mutant cells synthesized beta(1-2)glucan in vitro when exogenous UDP-glucose was added and contained the 235-kilodalton protein, which has been shown to carry out this synthesis in wild-type cells. We conclude that the inability of exoC mutants to synthesize beta(1-2)glucan is due to a deficiency in the activity of the enzyme phosphoglucomutase (EC 2.7.5.1), which in wild-type bacteria converts glucose 6-phosphate to glucose 1-phosphate, an intermediate in the synthesis of UDP-glucose. This interpretation can account for all of the deficiencies in polysaccharide synthesis which have been observed in these mutants.

Genetic analysis of the promoter region of the Bacillus subtilis alpha-amylase gene

The amyR2 allele of the Bacillus subtilis alpha-amylase cis-regulatory region enhances production of amylase and transcription of amyE, the structural gene, by two- to threefold over amyR1. The amylase gene bearing each of these alleles was cloned on plasmids of about 10 to 15 copies per chromosome. Transcription of the cloned amylase gene by each amyR allele was activated at the end of exponential growth and was subject to catabolite repression by glucose. The amount of amylase produced was roughly proportional to the copy number of the plasmid, and cells containing the amyR2-bearing plasmid, pAR2, produced two- to threefold more amylase than cells with the amyR1 plasmid, pAMY10. Deletion of DNA 5' to the alpha-amylase promoter, including deletion of the A + T-rich inverted repeat found in amyR1 and amyR2, had no effect on expression or transcription of alpha-amylase. Deletion of DNA 3' to the amyR1 promoter did not impair temporal activation of chloramphenicol acetyltransferase in amyR1-cat-86 transcriptional fusions, but catabolite repression was abolished. When an 8-base-pair linker was inserted in pAMY10 at the same site from which the 3' deletion was made, amylase expression doubled and was repressed less by glucose. Both the deletion and the insertion disrupted four bases at the 3' end of the putative amylase operator region. Site-directed mutagenesis was used to change bases in the promoter-operator region of amyR1 to their amyR2 counterparts. Either change alone increased amylase production twofold, but only the change at +7, next to the linker insertion of 3' deletion site, yielded the increased amylase activity in the presence of glucose that is characteristic of the amyR2 strain. The double mutant behaved most like strains carrying the amyR2 allele.

Cloning, sequencing, and disruption of the Bacillus subtilis sigma 28 gene

Bacillus subtilis contains multiple forms of RNA polymerase holoenzyme, distinguished by the presence of different specificity determinants known as sigma factors. The sigma 28 factor was initially purified as a unique transcriptional activity in vegetatively growing B. subtilis cells. Purification of the sigma 28 protein has allowed tryptic peptides to be prepared and sequenced. The sequence of one tryptic peptide fragment was used to prepare an oligonucleotide probe specific for the sigma 28 structural gene, and the gene was isolated from a B. subtilis subgenomic library. The complete nucleotide sequence of the sigma 28 gene was determined, and the cloned sigma 28 gene was used to construct a mutant strain which does not express the sigma 28 protein. This strain also failed to synthesize flagellin protein and grew as long filaments. The predicted sigma 28 gene product is a 254-amino-acid polypeptide with a calculated molecular weight of 29,500. The sigma 28 protein sequence was similar to that of other sequenced sigma factors and to the flbB gene product of Escherichia coli. Since the flbB gene product is a positive regulator of flagellar synthesis in E. coli, it is likely that sigma 28 functions to regulate flagellar synthesis in B. subtilis.

Genetic mapping by means of protoplast fusion in Bacillus subtilis

A new mapping method involving protoplast fusion in Bacillus subtilis is described. Protoplasts from an isogenic standard marker strain containing purA and from a strain containing both purB and the marker, "x", to be mapped were fused with polyethylene glycol, and purA+ purB+ fusants were selected. After isolation of single colonies and determination of unselected markers, marker x was mapped between two standard markers. This method was fully applicable to PBS1-resistant strains (e.g., lyt strains). The results obtained by protoplast fusion, conventional transformation and/or lysed protoplast transformation indicated that a lyt strain, Ni15, contained two new autolysin-minus mutations (lyt-151 and lyt-152). The properties of lyt-15 are also discussed.

Monovalent cations enable cell wall turnover of the turnover-deficient lyt-15 mutant of Bacillus subtilis

A lyt-15 mutant reported to be unable to turn over the cell wall exhibited the same rate of wall turnover as the standard strain if the medium contained 0.2 M NaCl, which did not affect growth. Cell wall autolysis was also optimal at 0.2 M NaCl.

Cell wall turnover in lyt mutants of Bacillus subtilis

One of the reported phenotypes of Bacillus subtilis strains containing the lyt mutations is a deficiency in cell wall turnover. However, it has recently been shown in our laboratory that these mutant cells can turn over their walls under certain conditions (Vitkovic et al. [2, 11] and Abstr. K3, Annu. Meet. Am. Soc. Microbiol., 1984, p. 147). I show in this paper that the long lag in wall turnover of lyt-1 (FJ3) and lyt-2 (FJ6) strains coincided with the time it took cells (which grow in long chains) to reach the end of exponential growth and to begin separating. At this time, the specific activity of N-acetylmuramyl-L-alanine amidase in the mutant strains reached the same level as in the standard strain in mid-exponential growth phase. Wall turnover was therefore probably caused by increased amidase activity. The turnover in strain lyt-15 (Nil5) was initiated by addition of NaCl and its rate reached that of the standard strain at 0.2 M NaCl. The amidase activities isolated from the lyt-15 and the standard strains varied similarly with NaCl concentration. When walls were probed with amidases and lysozyme in the presence of increasing concentrations of NaCl, the lyt-15 cell wall appeared to be very different from the walls of the standard strain or M. luteus (a standard lysozyme substrate). The results suggest that turnover deficiency in the lyt-15 strain may be due to a change in its wall resulting in a reversible resistance to turnover.

Genetic analysis of autolysin-deficient and flagellaless mutants of Bacillus subtilis

Three mutants with an autolysin-deficient and flagellaless phenotype (lyt) were genetically analyzed and compared with three thermosensitive flagellaless mutants. In view of the near indistinguishability of their phenotypes, all six mutations were assigned to fla loci. They were distributed into four linkage groups, designated flaA through flaD. flaA and flaB map between pyrD and thyA, flaD maps between aroD and lys, and, in agreement with a previous report, flaC maps near hisA. A locus associated with hypermotility, ifm-3, maps near the latter marker. Introduction of ifm-3 into lyt-1- and flaA4-containing strains led to partial suppression of the nonmotile phenotype. We discuss the possibility that the cellular concentration of autolysins is regulated by the expression of fla genes. Discrepancies with respect to previous mapping of flaA and flaB are accounted for.

Bacillus cereus electron transport and proton motive force during aerotaxis

Aerotaxis (migration towards oxygen) of Bacillus cereus M63, a motile strain, was inhibited by potassium cyanide and 2-heptyl-4-hydroxyquinoline N-oxide, indicating a requirement for both the terminal oxidase (cytochrome aa3) and the cytochrome b segment of the electron transport system. The concentration of oxygen that gave a half-maximal aerotactic response (K0.5) was 0.31 microM, which was similar to the Km for respiration (0.80 microM). The proton motive force increased from -135 to -177 mV when anaerobic cells were aerated, and it is proposed that the signal for aerotaxis is the increase in proton motive force that results from increased respiration. A strain of B. cereus T initially used in this study was immotile, grew as long chains of cells, and was deficient in autolytic enzyme. B. cereus M63 is a spontaneous derivative of B. cereus T that has normal motility.

Isolation and characterization of soluble peptidoglycan from several strains of Streptococcus faecium

Two phenotypically autolysis-deficient strains of Streptococcus faecium ATCC 9790 were shown to produce high-molecular-weight, soluble, linear, uncross-linked peptidoglycan when incubated with benzylpenicillin in a wall medium which permits cell wall synthesis (wall thickening) but not balanced growth. This high-molecular-weight s-peptidoglycan was shown to have a molecular weight of 46,000 to 54,000, lack peptide cross-links, and be virtually devoid of accessory wall polymers. It was hydrolyzed by hen egg white lysozyme and the endogenous, autolytic N-acetylmuramidase of S. faecium, but was not attacked by proteinases. Chemical analyses of the polymer are consistent with the following structure, where n is the number of repeating disaccharide units: (formula; see text).

Effects of lipophilic cations on motility and other physiological properties of Bacillus subtilis

Lipophilic cations (tetraphenylarsonium, tetraphenylphosphonium, and triphenylmethylphosphonium) caused a number of major changes in the physiology of Bacillus subtilis. Macromolecular synthesis was inhibited, adenosine 5'-triphosphate concentration increased, swimming speed was reduced, tumbling was suppressed, and the capacity to take up the cations was greatly enhanced; respiration was not significantly altered. The effects occurred at lipophilic cation concentrations in the range commonly employed for measurement of membrane potential. Neither the enhancement of cation uptake nor the motility inhibition was a consequence of alteration of membrane potential, since both effects were still seen in the presence of valinomycin, with the extent of 86Rb+ uptake indicating a constant potential. Because suppression of tumbling accompanied speed reduction, as has also been found when protonmotive force is reduced, it is likely that lipophilic cations are perturbing the process of conversion of proton energy into work, rather than simply causing structural damage.