Characterization of CidR-mediated regulation in Bacillus anthracis reveals a previously undetected role of S-layer proteins as murein hydrolases

Interface-mediated protein aggregation

The aggregation of proteins at interfaces has significant roles and can also lead to dysfunction of different physiological processes. The interfacial effects on the assembly and aggregation of biopolymers are not only crucial for a comprehensive understanding of protein biological functions, but also hold great potential for advancing the state-of-the-art applications of biopolymer materials. Recently, there has been remarkable progress in a collaborative context, as we strive to gain control over complex interfacial assembly structures of biopolymers. These biopolymer structures range from the nanoscale to mesoscale and even macroscale, and are attained through the rational design of interactions between biological building blocks and surfaces/interfaces. This review spotlights the recent advancements in interface-mediated assembly and properties of biopolymer materials. Initially, we introduce the solid-liquid interface (SIL)-mediated biopolymer assembly that includes the inorganic crystalline template effect and protein self-adoptive deposition through phase transition. Next, we display the advancement of biopolymer assembly instigated by the air-water interface (AWI) that acts as an energy conversion station. Lastly, we discuss succinctly the assembly of biopolymers at the liquid-liquid interface (LLI) along with their applications. It is our hope that this overview will stimulate the integration and progression of the science of interfacial assembled biopolymer materials and surfaces/interfaces.

S-layer proteins as immune players: tales from pathogenic and non-pathogenic bacteria

In bacteria, as in other microorganisms, surface compounds interact with different pattern recognition receptors expressed by host cells, which usually triggers a variety of cellular responses that result in immunomodulation. The S-layer is a two-dimensional macromolecular crystalline structure formed by (glyco)-protein subunits that covers the surface of many species of Bacteria and almost all Archaea. In Bacteria, the presence of S-layer has been described in both pathogenic and non-pathogenic strains. As surface components, special attention deserves the role that S-layer proteins (SLPs) play in the interaction of bacterial cells with humoral and cellular components of the immune system. In this sense, some differences can be predicted between pathogenic and non-pathogenic bacteria. In the first group, the S-layer constitutes an important virulence factor, which in turn makes it a potential therapeutic target. For the other group, the growing interest to understand the mechanisms of action of commensal microbiota and probiotic strains has prompted the studies of the role of the S-layer in the interaction between the host immune cells and bacteria bearing this surface structure. In this review, we aim to summarize the main latest reports and the perspectives of bacterial SLPs as immune players, focusing on those from pathogenic and commensal/probiotic most studied species.

McbG, a LysR Family Transcriptional Regulator, Activates the mcbBCDEF Gene Cluster Involved in the Upstream Pathway of Carbaryl Degradation in Pseudomonas sp. Strain XWY-1

Although enzyme-encoding genes involved in the degradation of carbaryl have been reported in Pseudomonas sp. strain XWY-1, no regulator has been identified yet. In the mcbABCDEF cluster responsible for the upstream pathway of carbaryl degradation (from carbaryl to salicylate), the mcbA gene is constitutively expressed, while mcbBCDEF is induced by 1-naphthol, the hydrolysis product of carbaryl by McbA. In this study, we identified McbG, a transcriptional activator of the mcbBCDEF cluster. McbG is a 315-amino-acid protein with a molecular mass of 35.7 kDa. It belongs to the LysR family of transcriptional regulators and shows 28.48% identity to the pentachlorophenol (PCP) degradation transcriptional activation protein PcpR from Sphingobium chlorophenolicum ATCC 39723. Gene disruption and complementation studies reveal that mcbG is essential for transcription of the mcbBCDEF cluster in response to 1-naphthol in strain XWY-1. The results of the electrophoretic mobility shift assay (EMSA) and DNase I footprinting show that McbG binds to the 25-bp motif in the mcbBCDEF promoter area. The palindromic sequence TATCGATA within the motif is essential for McbG binding. The binding site is located between the -10 box and the transcription start site. In addition, McbG can repress its own transcription. The EMSA results show that a 25-bp motif in the mcbG promoter area plays an important role in McbG binding to the promoter of mcbG This study reveals the regulatory mechanism for the upstream pathway of carbaryl degradation in strain XWY-1. The identification of McbG increases the variety of regulatory models within the LysR family of transcriptional regulators.IMPORTANCE Pseudomonas sp. strain XWY-1 is a carbaryl-degrading strain that utilizes carbaryl as the sole carbon and energy source for growth. The functional genes involved in the degradation of carbaryl have already been reported. However, the regulatory mechanism has not been investigated yet. Previous studies demonstrated that the mcbA gene, responsible for hydrolysis of carbaryl to 1-naphthol, is constitutively expressed in strain XWY-1. In this study, we identified a LysR-type transcriptional regulator, McbG, which activates the mcbBCDEF gene cluster responsible for the degradation of 1-naphthol to salicylate and represses its own transcription. The DNA binding site of McbG in the mcbBCDEF promoter area contains a palindromic sequence, which affects the binding of McbG to DNA. These findings enhance our understanding of the mechanism of microbial degradation of carbaryl.

Inactivation of the Pta-AckA pathway impairs fitness of Bacillus anthracis during overflow metabolism

Under conditions of glucose excess, aerobically growing bacteria predominantly direct carbon flux towards acetate fermentation, a phenomenon known as overflow metabolism or the bacterial 'Crabtree effect'. Numerous studies of the major acetate-generating pathway, the Pta-AckA, revealed its important role in bacterial fitness through the control of central metabolism to sustain balanced growth and cellular homeostasis. In this work, we highlight the contribution of the Pta-AckA pathway to fitness of the spore-forming bacterium, Bacillus anthracis We demonstrate that disruption of the Pta-AckA pathway causes a drastic growth reduction in the mutants and alters the metabolic and energy status of the cells. Our results revealed that inactivation of the Pta-AckA pathway increases the glucose consumption rate, affects intracellular ATP, NAD⁺ and NADH levels and leads to a metabolic block at the pyruvate and acetyl-CoA nodes. Consequently, accumulation of intracellular acetyl-CoA and pyruvate forces bacteria to direct carbon into the TCA and/or glyoxylate cycles as well as fatty acid and poly(3-hydroxybutyrate) (PHB) biosynthesis pathways. Notably, the presence of phosphate butyryltransferase in B. anthracis partially compensates for the loss of phosphotransacetylase activity. Furthermore, overexpression of the ptb gene not only eliminates the negative impact of the pta mutation on B. anthracis fitness, but also restores normal growth in the pta mutant of the non-butyrate-producing bacterium, Staphylococcus aureus Taken together, the results of this study demonstrate the importance of the Pta-AckA pathway for B. anthracis fitness by revealing its critical contribution to the maintenance of metabolic homeostasis during aerobic growth under conditions of carbon overflow.IMPORTANCE B. anthracis, the etiologic agent of anthrax, is a highly pathogenic, spore-forming bacterium that causes acute, life-threatening disease in both humans and livestock. A greater understanding of the metabolic determinants governing fitness of B. anthracis is essential for the development of successful therapeutic and vaccination strategies aimed at lessening the potential impact of this important biodefense pathogen. This study is the first to demonstrate the vital role of the Pta-AckA pathway in preserving energy and metabolic homeostasis in B. anthracis under conditions of carbon overflow, therefore, highlighting this pathway as a potential therapeutic target for drug discovery. Overall, the results of this study provide important insight into understanding the metabolic processes and requirements driving rapid B. anthracis proliferation during vegetative growth.

The Two Distinct Types of SecA2-Dependent Export Systems

In addition to SecA of the general Sec system, many Gram-positive bacteria, including mycobacteria, express SecA2, a second, transport-associated ATPase. SecA2s can be subdivided into two mechanistically distinct types: (i) SecA2s that are part of the accessory Sec (aSec) system, a specialized transporter mediating the export of a family of serine-rich repeat (SRR) glycoproteins that function as adhesins, and (ii) SecA2s that are part of multisubstrate systems, in which SecA2 interacts with components of the general Sec system, specifically the SecYEG channel, to export multiple types of substrates. Found mainly in streptococci and staphylococci, the aSec system also contains SecY2 and novel accessory Sec proteins (Asps) that are required for optimal export. Asp2 also acetylates glucosamine residues on the SRR domains of the substrate during transport. Targeting of the SRR substrate to SecA2 and the aSec translocon is mediated by a specialized signal peptide. Multisubstrate SecA2 systems are present in mycobacteria, corynebacteria, listeriae, clostridia, and some bacillus species. Although most substrates for this SecA2 have canonical signal peptides that are required for export, targeting to SecA2 appears to depend on structural features of the mature protein. The feature of the mature domains of these proteins that renders them dependent on SecA2 for export may be their potential to fold in the cytoplasm. The discovery of aSec and multisubstrate SecA2 systems expands our appreciation of the diversity of bacterial export pathways. Here we present our current understanding of the mechanisms of each of these SecA2 systems.

Transcriptional profiling of the clpX mutant in Bacillus anthracis reveals regulatory connection with the lrgAB operon

ClpX functions as either an independent chaperone or a component of the ClpXP protease, a conserved intracellular protease that acts as a global regulator in the bacterial cell by degrading regulatory proteins, stress response proteins and rate-limiting enzymes. Previously, we found that loss of clpX in Bacillus anthracis Sterne leads to increased susceptibility to antimicrobial agents that target the cell envelope. The aim of this study was to identify genes within the regulatory network of clpX that contribute to antimicrobial resistance. Using microarray analysis, we found 119 genes that are highly differentially expressed in the ∆clpX mutant, with the majority involved in metabolic, transport or regulatory functions. Several of these differentially expressed genes, including glpF, sigM, mrsA, lrgA and lrgB, are associated with cell wall-active antibiotics in other bacterial species. We focused on lrgA and lrgB, which form the lrgAB operon and are downregulated in ∆clpX, because loss of lrgAB increases autolytic activity and penicillin susceptibility in Staphylococcus aureus. While we observed no changes in autolytic activity in either ∆clpX or ∆lrgAB B. anthracis Sterne, we find that both mutants have increased susceptibility to the antimicrobial peptide LL-37 and daptomycin. However, phenotypes between ∆clpX and ∆lrgAB are not identical as ∆clpX also displays increased susceptibility to penicillin and nisin but ∆lrgAB does not. Therefore, while decreased expression of lrgAB may be partially responsible for the increased antimicrobial susceptibility seen in the ∆clpX mutant, disruption of other pathways must also contribute to this phenotype.

The CodY-dependent clhAB2 operon is involved in cell shape, chaining and autolysis in Bacillus cereus ATCC 14579

The Gram-positive pathogen Bacillus cereus is able to grow in chains of rod-shaped cells, but the regulation of chaining remains largely unknown. Here, we observe that glucose-grown cells of B. cereus ATCC 14579 form longer chains than those grown in the absence of glucose during the late exponential and transition growth phases, and identify that the clhAB₂ operon is required for this chain lengthening phenotype. The clhAB₂ operon is specific to the B. cereus group (i.e., B. thuringiensis, B. anthracis and B. cereus) and encodes two membrane proteins of unknown function, which are homologous to the Staphylococcus aureus CidA and CidB proteins involved in cell death control within glucose-grown cells. A deletion mutant (ΔclhAB₂) was constructed and our quantitative image analyses show that ΔclhAB₂ cells formed abnormal short chains regardless of the presence of glucose. We also found that glucose-grown cells of ΔclhAB₂ were significantly wider than wild-type cells (1.47 μm ±CI_95% 0.04 vs 1.19 μm ±CI_95% 0.03, respectively), suggesting an alteration of the bacterial cell wall. Remarkably, ΔclhAB₂ cells showed accelerated autolysis under autolysis-inducing conditions, compared to wild-type cells. Overall, our data suggest that the B. cereus clhAB₂ operon modulates peptidoglycan hydrolase activity, which is required for proper cell shape and chain length during cell growth, and down-regulates autolysin activity. Lastly, we studied the transcription of clhAB₂ using a lacZ transcriptional reporter in wild-type, ccpA and codY deletion-mutant strains. We found that the global transcriptional regulatory protein CodY is required for the basal level of clhAB₂ expression under all conditions tested, including the transition growth phase while CcpA, the major global carbon regulator, is needed for the high-level expression of clhAB₂ in glucose-grown cells.

Modification of the Streptococcus mutans transcriptome by LrgAB and environmental stressors

The Streptococcus mutans Cid/Lrg system is central to the physiology of this cariogenic organism, affecting oxidative stress resistance, biofilm formation and competence. Previous transcriptome analyses of lytS (responsible for the regulation of lrgAB expression) and cidB mutants have revealed pleiotropic effects on carbohydrate metabolism and stress resistance genes. In this study, it was found that an lrgAB mutant, previously shown to have diminished aerobic and oxidative stress growth, was also much more growth impaired in the presence of heat and vancomycin stresses, relative to wild-type, lrgA and lrgB mutants. To obtain a more holistic picture of LrgAB and its involvement in stress resistance, RNA sequencing and bioinformatics analyses were used to assess the transcriptional response of wild-type and isogenic lrgAB mutants under anaerobic (control) and stress-inducing culture conditions (aerobic, heat and vancomycin). Hierarchical clustering and principal components analyses of all differentially expressed genes revealed that the most distinct gene expression profiles between S. mutans UA159 and lrgAB mutant occurred during aerobic and high-temperature growth. Similar to previous studies of a cidB mutant, lrgAB stress transcriptomes were characterized by a variety of gene expression changes related to genomic islands, CRISPR-C as systems, ABC transporters, competence, bacteriocins, glucosyltransferases, protein translation, tricarboxylic acid cycle, carbohydrate metabolism/storage and transport. Notably, expression of lrgAB was upregulated in the wild-type strain under all three stress conditions. Collectively, these results demonstrate that mutation of lrgAB alters the transcriptional response to stress, and further support the idea that the Cid/Lrg system acts to promote cell homeostasis in the face of environmental stress.

Diversity in S-layers

Surface layers, referred simply as S-layers, are the two-dimensional crystalline arrays of protein or glycoprotein subunits on cell surface. They are one of the most common outermost envelope components observed in prokaryotic organisms (Archaea and Bacteria). Over the past decades, S-layers have become an issue of increasing interest due to their ubiquitousness, special features and functions. Substantial work in this field provides evidences of an enormous diversity in S-layers. This paper reviews and illustrates the diversity from several different aspects, involving the S-layer-carrying strains, the structure of S-layers, the S-layer proteins and genes, as well as the functions of S-layers.

Biogenesis and functions of bacterial S-layers

The outer surface of many archaea and bacteria is coated with a proteinaceous surface layer (known as an S-layer), which is formed by the self-assembly of monomeric proteins into a regularly spaced, two-dimensional array. Bacteria possess dedicated pathways for the secretion and anchoring of the S-layer to the cell wall, and some Gram-positive species have large S-layer-associated gene families. S-layers have important roles in growth and survival, and their many functions include the maintenance of cell integrity, enzyme display and, in pathogens and commensals, interaction with the host and its immune system. In this Review, we discuss our current knowledge of S-layer and related proteins, including their structures, mechanisms of secretion and anchoring and their diverse functions.

Functional characterization of WalRK: A two-component signal transduction system from Bacillus anthracis

Two-component signal transduction systems (TCS), consisting of a sensor histidine protein kinase and its cognate response regulator, are an important mode of environmental sensing in bacteria. Additionally, they have been found to regulate virulence determinants in several pathogens. Bacillus anthracis, the causative agent of anthrax and a bioterrorism agent, harbours 41 pairs of TCS. However, their role in its pathogenicity has remained largely unexplored. Here, we show that WalRK of B. anthracis forms a functional TCS which exhibits some species-specific functions. Biochemical studies showed that domain variants of WalK, the histidine kinase, exhibit classical properties of autophosphorylation and phosphotransfer to its cognate response regulator WalR. Interestingly, these domain variants also show phosphatase activity towards phosphorylated WalR, thereby making WalK a bifunctional histidine kinase/phosphatase. An in silico regulon determination approach, using a consensus binding sequence from Bacillus subtilis, provided a list of 30 genes that could form a putative WalR regulon in B. anthracis. Further, electrophoretic mobility shift assay was used to show direct binding of purified WalR to the upstream regions of three putative regulon candidates, an S-layer protein EA1, a cell division ABC transporter FtsE and a sporulation histidine kinase KinB3. Our work lends insight into the species-specific functions and mode of action of B. anthracis WalRK.

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WalRK forms a functional TCS in B. anthracis, expressed throughout the growth phase.

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WalK variants exhibit autophosphorylation and phosphotransfer to WalR.

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WalKc variants also show phosphatase activity towards phosphorylated WalR.

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A potential WalR regulon in B. anthracis was predicted in silico.

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DNA binding ability was demonstrated for WalR.

Secreted proteases control autolysin-mediated biofilm growth of Staphylococcus aureus

Staphylococcus epidermidis, a commensal of humans, secretes Esp protease to prevent Staphylococcus aureus biofilm formation and colonization. Blocking S. aureus colonization may reduce the incidence of invasive infectious diseases; however, the mechanism whereby Esp disrupts biofilms is unknown. We show here that Esp cleaves autolysin (Atl)-derived murein hydrolases and prevents staphylococcal release of DNA, which serves as extracellular matrix in biofilms. The three-dimensional structure of Esp was revealed by x-ray crystallography and shown to be highly similar to that of S. aureus V8 (SspA). Both atl and sspA are necessary for biofilm formation, and purified SspA cleaves Atl-derived murein hydrolases. Thus, S. aureus biofilms are formed via the controlled secretion and proteolysis of autolysin, and this developmental program appears to be perturbed by the Esp protease of S. epidermidis.

Lactobacillus surface layer proteins: structure, function and applications

Bacterial surface (S) layers are the outermost proteinaceous cell envelope structures found on members of nearly all taxonomic groups of bacteria and Archaea. They are composed of numerous identical subunits forming a symmetric, porous, lattice-like layer that completely covers the cell surface. The subunits are held together and attached to cell wall carbohydrates by non-covalent interactions, and they spontaneously reassemble in vitro by an entropy-driven process. Due to the low amino acid sequence similarity among S-layer proteins in general, verification of the presence of an S-layer on the bacterial cell surface usually requires electron microscopy. In lactobacilli, S-layer proteins have been detected on many but not all species. Lactobacillus S-layer proteins differ from those of other bacteria in their smaller size and high predicted pI. The positive charge in Lactobacillus S-layer proteins is concentrated in the more conserved cell wall binding domain, which can be either N- or C-terminal depending on the species. The more variable domain is responsible for the self-assembly of the monomers to a periodic structure. The biological functions of Lactobacillus S-layer proteins are poorly understood, but in some species S-layer proteins mediate bacterial adherence to host cells or extracellular matrix proteins or have protective or enzymatic functions. Lactobacillus S-layer proteins show potential for use as antigen carriers in live oral vaccine design because of their adhesive and immunomodulatory properties and the general non-pathogenicity of the species.

S-layer homology motif is an immunogen and confers protection to mouse model against anthrax

SLH proteins bear an S-layer homology motif comprised of three S-layer homology (SLH) domains. Several SLH proteins in Bacillus anthracis have been recognized as immunogenic in recent past. We hypothesized that the SLH motif, the most common moiety amongst all the SLH proteins could be responsible for their immunogenicity. To test this hypothesis, we checked the immunogenic capacity of recombinant SLH motif. The rSLH fragment on immunization in mice led to the development of a potent humoral and T Helper immune response as compared to the only adjuvant immunized group. Antibodies raised against rSLH could identify the surface of B. anthracis Ames strain vegetative forms. rSLH immunization protected 50% mice challenged with B. anthracis compared to 0% survival in group of mice immunized with only adjuvant. But when rSLH immunization was synergized with a single sub-optimal dose of rPA (Protective Antigen), 80% immunized mice survived the lethal challenge of B. anthracis. Taken together, for the first time we demonstrate the immunogenic and protective potential of SLH motif of the SLH proteins of B. anthracis.

Disruption of the alsSD operon of Enterococcus faecalis impairs growth on pyruvate at low pH

Diacetyl and acetoin are pyruvate-derived metabolites excreted by many micro-organisms, and are important in their physiology. Although generation of these four-carbon (C4) compounds in Enterococcus faecalis is a well-documented phenotype, little is known about the gene regulation of their biosynthetic pathway and the physiological role of the pathway in this bacterium. In this work, we identified the genes involved in C4 compound biosynthesis in Ent. faecalis and report their transcriptional analysis. These genes are part of the alsSD bicistronic operon, which encodes α-acetolactate synthase (AlsS) and α-acetolactate decarboxylase (AlsD). Our studies showed that alsSD operon transcription levels are maximal during the exponential phase of growth, decreasing thereafter. Furthermore, we found that this transcription is enhanced upon addition of pyruvate to the growth medium. In order to study the functional role of the alsSD operon, an isogenic alsSD mutant strain was constructed. This strain lost its capacity to generate C4 compounds, confirming the role of alsSD genes in this metabolic pathway. In contrast to the wild-type strain, the alsSD-deficient strain was unable to grow in LB medium supplemented with pyruvate at an initial pH of 4.5. This dramatic reduction in growth parameters for the mutant strain was simultaneously accompanied by the inability to alkalinize the internal and external medium under these conditions. In sum, these results suggest that the decarboxylation reactions related to the C4 biosynthetic pathway give enterococcal cells a competitive advantage during pyruvate metabolism at low pH.

The SLH-domain protein BslO is a determinant of Bacillus anthracis chain length

The Gram-positive pathogen Bacillus anthracis grows in characteristic chains of individual, rod-shaped cells. Here, we report the cell-separating activity of BslO, a putative N-acetylglucosaminidase bearing three N-terminal S-layer homology (SLH) domains for association with the secondary cell wall polysaccharide (SCWP). Mutants with an insertional lesion in the bslO gene exhibit exaggerated chain lengths, although individual cell dimensions are unchanged. Purified BslO complements this phenotype in trans, effectively dispersing chains of bslO-deficient bacilli without lysis and localizing to the septa of vegetative cells. Compared with the extremely long chain lengths of csaB bacilli, which are incapable of binding proteins with SLH-domains to SCWP, bslO mutants demonstrate a chaining phenotype that is intermediate between wild-type and csaB. Computational simulation suggests that BslO effects a non-random distribution of B. anthracis chain lengths, implying that all septa are not equal candidates for separation.

O-Acetylation of peptidoglycan is required for proper cell separation and S-layer anchoring in Bacillus anthracis

O-Acetylation of the MurNAc moiety of peptidoglycan is typically associated with bacterial resistance to lysozyme, a muramidase that serves as a central component of innate immunity. Here, we report that the peptidoglycan of Bacillus anthracis, the etiological agent of anthrax, is O-acetylated and that, unusually, this modification is produced by two unrelated families of O-acetyltransferases. Also, in contrast to other bacteria, O-acetylation of B. anthracis peptidoglycan is combined with N-deacetylation to confer resistance of cells to lysozyme. Activity of the Pat O-acetyltransferases is required for the separation of the daughter cells following bacterial division and for anchoring of one of the major S-layer proteins. Our results indicate that peptidoglycan O-acetylation modulates endogenous muramidase activity affecting the cell-surface properties and morphology of this important pathogen.

The surface of Bacillus anthracis

Bacillus anthracis is a Gram positive organism possessing a complex parietal structure. An S-layer, a bi-dimensional crystalline layer, and a peptidic capsule surround the thick peptidoglycan of bacilli harvested during infection. A review of the current literature indicates that elements from each of these three structures, as well as membrane components, have been studied. So-called cell-wall secondary polymers, be they attached to the cell-wall or to the membrane play important functions, either per se or because they permit the anchoring of proteins. Some surface proteins, whichever compartment they are attached to, play, as had been hypothesized, key roles in virulence. Others, of yet unknown function, are nevertheless expressed in vivo. This review will focus on well-studied polymers or proteins and indicate, when appropriate, the mechanisms by which they are targeted to their respective locations.

An overlap between the control of programmed cell death in Bacillus anthracis and sporulation

The Staphylococcus aureus cid and lrg operons have been shown to control cell death and lysis in a manner thought to be analogous to programmed cell death (apoptosis) in eukaryotic organisms. Although orthologous operons are present in a wide variety of bacterial species, members of the Bacillus cereus group are unique in that they have a total of four cid-/lrg-like operons. Two of these operons are similar to the S. aureus cid and lrg operons, while the other two (designated clhAB(1) and clhAB(2)) are unique to this group. In the present study, the functions and regulation of these loci were examined. Interestingly, the Bacillus anthracis lrgAB mutant displayed decreased stationary-phase survival, whereas the clhAB(2) mutant exhibited increased stationary-phase survival compared to the parental and complementation strains. However, neither mutation had a dramatic effect on murein hydrolase activity or autolysis. Furthermore, a quantitative analysis of the sporulation efficiency revealed that both mutants formed fewer spores than did the parental strain. Similar to S. aureus, B. anthracis lrgAB transcription was shown to be induced by gramicidin and CCCP, agents known to dissipate the proton motive force, in a lytSR-dependent manner. Northern blot analyses also demonstrated a positive role for lytSR in the clhAB(2) transcription. Taken together, the results of the present study demonstrate that B. anthracis lrgAB and clhAB(2) play important roles in the control of cell death and lysis and reveal a previously unrecognized role of this system in sporulation.

Structure and function of the LysR-type transcriptional regulator (LTTR) family proteins

The LysR family of transcriptional regulators represents the most abundant type of transcriptional regulator in the prokaryotic kingdom. Members of this family have a conserved structure with an N-terminal DNA-binding helix-turn-helix motif and a C-terminal co-inducer-binding domain. Despite considerable conservation both structurally and functionally, LysR-type transcriptional regulators (LTTRs) regulate a diverse set of genes, including those involved in virulence, metabolism, quorum sensing and motility. Numerous structural and transcriptional studies of members of the LTTR family are helping to unravel a compelling paradigm that has evolved from the original observations and conclusions that were made about this family of transcriptional regulators.

Murein hydrolase activity in the surface layer of Lactobacillus acidophilus ATCC 4356

We describe a new enzymatic functionality for the surface layer (S-layer) of Lactobacillus acidophilus ATCC 4356, namely, an endopeptidase activity against the cell wall of Salmonella enterica serovar Newport, assayed via zymograms and identified by Western blotting. Based on amino acid sequence comparisons, the hydrolase activity was predicted to be located at the C terminus. Subsequent cloning and expression of the C-terminal domain in Bacillus subtilis resulted in the functional verification of the enzymatic activity.

A new group of parasporal inclusions encoded by the S-layer gene of Bacillus thuringiensis

Bacillus thuringiensis produces various groups of active proteins, such as Cyt, Vip and Parasporin, in addition to the Cry protein. In this study we show S-layer proteins to be a new group of parasporal inclusions of B. thuringiensis. The S-layer consists of a two-dimensional lattice structure and is the outermost component of many archaeobacteria and eubacteria. The parasporal inclusion of B. thuringiensis strain CTC was found to be not a typical crystal protein encoded by the cry gene, but a proteinaceous inclusion encoded by the S-layer gene. Furthermore, the CTC-like strains (with their parasporal inclusions coded by the S-layer gene) are widely distributed and accounted for 25.4% of the B. thuringiensis strains tested. These strains constitute a new group of parasporal inclusions encoded by the S-layer gene of B. thuringiensis and shed new light on B. thuringiensis nontoxic strains.