Assembly and interactions of cotJ-encoded proteins, constituents of the inner layers of the Bacillus subtilis spore coat

New insights into peroxide toxicology: sporulenes help Bacillus subtilis endospores from hydrogen peroxide

AIM

The purpose of the present study was to understand the possible events involved in the toxicity of hydrogen peroxide (H2O2) to wild and sporulene-deficient spores of Bacillus subtilis, as H2O2 was previously shown to have deleterious effects.

METHODS AND RESULTS

The investigation utilized two strains of B. subtilis, namely the wild-type PY79 (WT) and the sporulene-deficient TB10 (ΔsqhC mutant). Following treatment with 0.05% H2O2 (v/v), spore viability was assessed using a plate count assay, which revealed a significant decrease in cultivability of 80% for the ΔsqhC mutant spores. Possible reasons for the loss of spore viability were investigated with microscopic analysis, dipicholinic acid (DPA) quantification and propidium iodide (PI) staining. Microscopic examinations revealed the presence of withered and deflated morphologies in spores of ΔsqhC mutants treated with H2O2, indicating a compromised membrane permeability. This was further substantiated by the absence of DPA and a high frequency (50%-75%) of PI infiltration. The results of fatty acid methyl ester analysis and protein profiling indicated that the potentiation of H2O2-induced cellular responses was manifested in the form of altered spore composition in ΔsqhC B. subtilis. The slowed growth rates of the ΔsqhC mutant and the heightened sporulene biosynthesis pathways in the WT strain, both upon exposure to H2O2, suggested a protective function for sporulenes in vegetative cells.

CONCLUSIONS

Sporulenes serve as a protective layer for the inner membrane of spores, thus assuming a significant role in mitigating the adverse effects of H2O2 in WT B. subtilis. The toxic effects of H2O2 were even more pronounced in the spores of the ΔsqhC mutant, which lacks this protective barrier of sporulenes.

Application and potential of multifrequency ultrasound in juice industry: Comprehensive analysis of inactivation and germination of Alicyclobacillus acidoterrestris spores

The majority of acidic fruits are perishable owing to their high-water activity, which promotes microbial activity, thus exhibiting metabolic functions that cause spoilage. Along with sanitary practices, several treatments are used during processing and/or storage to inhibit the development of undesirable bacteria. To overcome the challenges caused by mild heat treatment, juice manufacturers have recently increased their involvement in developing novel non-thermal processing procedures. Ultrasonication alone or in combination with other hurdle technologies may be used to pasteurize processed fruit juices. Multifrequency ultrasound has gained popularity due to the fact that mono-frequency ultrasound has less impact on bacterial inactivation and bioactive compound enhancement of fruit juice. Here, we present and discuss the fundamental information and technological knowledge of how spoilage bacteria, specifically Alicyclobacillus acidoterrestris, assemble resistant spores and inactivate and germinate dormant spores in response to nutrient germinants and physical treatments such as heat and ultrasound. To the authors' knowledge, no prior review of ultrasonic inactivation and germination of A. acidoterrestris in fruit juice exists. Therefore, this article aims to provide a review of previously published research on the inactivation and germination of A. acidoterrestris in fruit juice by ultrasound and heat.

Henriques A. A protein phosphorylation module patterns the Bacillus subtilis spore outer coat

Assembly of the Bacillus subtilis spore coat involves over 80 proteins which self-organize into a basal layer, a lamellar inner coat, a striated electrodense outer coat and a more external crust. CotB is an abundant component of the outer coat. The C-terminal moiety of CotB, SKRB , formed by serine-rich repeats, is polyphosphorylated by the Ser/Thr kinase CotH. We show that another coat protein, CotG, with a central serine-repeat region, SKRG , interacts with the C-terminal moiety of CotB and promotes its phosphorylation by CotH in vivo and in a heterologous system. CotG itself is phosphorylated by CotH but phosphorylation is enhanced in the absence of CotB. Spores of a strain producing an inactive form of CotH, like those formed by a cotG deletion mutant, lack the pattern of electrondense outer coat striations, but retain the crust. In contrast, deletion of the SKRB region, has no major impact on outer coat structure. Thus, phosphorylation of CotG by CotH is a key factor establishing the structure of the outer coat. The presence of the cotB/cotH/cotG cluster in several species closely related to B. subtilis hints at the importance of this protein phosphorylation module in the morphogenesis of the spore surface layers.

Diversity and evolutionary dynamics of spore-coat proteins in spore-forming species of Bacillales

Among members of the Bacillales order, there are several species capable of forming a structure called an endospore. Endospores enable bacteria to survive under unfavourable growth conditions and germinate when environmental conditions are favourable again. Spore-coat proteins are found in a multilayered proteinaceous structure encasing the spore core and the cortex. They are involved in coat assembly, cortex synthesis and germination. Here, we aimed to determine the diversity and evolutionary processes that have influenced spore-coat genes in various spore-forming species of Bacillales using an in silico approach. For this, we used sequence similarity searching algorithms to determine the diversity of coat genes across 161 genomes of Bacillales. The results suggest that among Bacillales, there is a well-conserved core genome, composed mainly by morphogenetic coat proteins and spore-coat proteins involved in germination. However, some spore-coat proteins are taxa-specific. The best-conserved genes among different species may promote adaptation to changeable environmental conditions. Because most of the Bacillus species harbour complete or almost complete sets of spore-coat genes, we focused on this genus in greater depth. Phylogenetic reconstruction revealed eight monophyletic groups in the Bacillus genus, of which three are newly discovered. We estimated the selection pressures acting over spore-coat genes in these monophyletic groups using classical and modern approaches and detected horizontal gene transfer (HGT) events, which have been further confirmed by scanning the genomes to find traces of insertion sequences. Although most of the genes are under purifying selection, there are several cases with individual sites evolving under positive selection. Finally, the HGT results confirm that sporulation is an ancestral feature in Bacillus.

Regulation of expression of a select group of Bacillus anthracis spore coat proteins

The spore coat of Bacilli is a relatively complex structure comprised of about 70 species of proteins in 2 or 3 layers. While some are involved in assembly or protection, the regulation of many are not well defined so lacZ transcriptional fusions were constructed to six Bacillus anthracis spore coat genes in order to gain insight into their possible functions. The genes were selected on the basis of the location of the encoded proteins within the coat and distribution among spore forming species. Conditions tested were temperature and media either as solid or liquid. The most extensive differences were for the relatively well expressed fusions to the cotH and cotM genes, which were greatest at 30°C on plates of a nutrient rich medium. The cotJ operon was moderately expressed under all conditions although somewhat higher on enriched plates at 30°C. Cot S was low under all conditions except for a substantial increase in biofilm medium. Cot∝ and cotF were essentially invariant with a somewhat greater expression in the more enriched medium. The capacity of a subset of coat genes to respond to various conditions reflects a flexibility in spore coat structure that may be necessary for adaptation to environmental challenges. This could account, at least in part, for the complexity of this structure.

A LysM Domain Intervenes in Sequential Protein-Protein and Protein-Peptidoglycan Interactions Important for Spore Coat Assembly in Bacillus subtilis

At a late stage in spore development in Bacillus subtilis, the mother cell directs synthesis of a layer of peptidoglycan known as the cortex between the two forespore membranes, as well as the assembly of a protective protein coat at the surface of the forespore outer membrane. SafA, the key determinant of inner coat assembly, is first recruited to the surface of the developing spore and then encases the spore under the control of the morphogenetic protein SpoVID. SafA has a LysM peptidoglycan-binding domain, SafA_LysM, and localizes to the cortex-coat interface in mature spores. SafA_LysM is followed by a region, A, required for an interaction with SpoVID and encasement. We now show that residues D10 and N30 in SafA_LysM, while involved in the interaction with peptidoglycan, are also required for the interaction with SpoVID and encasement. We further show that single alanine substitutions on residues S11, L12, and I39 of SafA_LysM that strongly impair binding to purified cortex peptidoglycan affect a later stage in the localization of SafA that is also dependent on the activity of SpoVE, a transglycosylase required for cortex formation. The assembly of SafA thus involves sequential protein-protein and protein-peptidoglycan interactions, mediated by the LysM domain, which are required first for encasement then for the final localization of the protein in mature spores.IMPORTANCE Bacillus subtilis spores are encased in a multiprotein coat that surrounds an underlying peptidoglycan layer, the cortex. How the connection between the two layers is enforced is not well established. Here, we elucidate the role of the peptidoglycan-binding LysM domain, present in two proteins, SafA and SpoVID, that govern the localization of additional proteins to the coat. We found that SafA_LysM is a protein-protein interaction module during the early stages of coat assembly and a cortex-binding module at late stages in morphogenesis, with the cortex-binding function promoting a tight connection between the cortex and the coat. In contrast, SpoVID_LysM functions only as a protein-protein interaction domain that targets SpoVID to the spore surface at the onset of coat assembly.

SpoVID functions as a non-competitive hub that connects the modules for assembly of the inner and outer spore coat layers in Bacillus subtilis

During sporulation in Bacillus subtilis, a group of mother cell‐specific proteins guides the assembly of the coat, a multiprotein structure that protects the spore and influences many of its environmental interactions. SafA and CotE behave as party hubs, governing assembly of the inner and outer coat layers. Targeting of coat proteins to the developing spore is followed by encasement. Encasement by SafA and CotE requires E, a region of 11 amino acids in the encasement protein SpoVID, with which CotE interacts directly. Here, we identified two single alanine substitutions in E that prevent binding of SafA, but not of CotE, to SpoVID, and block encasement. The substitutions result in the accumulation of SafA, CotE and their dependent proteins at the mother cell proximal spore pole, phenocopying a spoVID null mutant and suggesting that mislocalized SafA acts as an attractor for the rest of the coat. The requirement for E in SafA binding is bypassed by a peptide with the sequence of E provided in trans. We suggest that E allows binding of SafA to a second region in SpoVID, enabling CotE to interact with E and SpoVID to function as a non‐competitive hub during spore encasement.

Autoregulation of SafA Assembly through Recruitment of a Protein Cross-Linking Enzyme

The coat of Bacillus subtilis spores is a multiprotein protective structure that also arbitrates many of the environmental interactions of the spore. The coat assembles around the cortex peptidoglycan layer and is differentiated into an inner and an outer layer and a crust. SafA governs assembly of the inner coat, whereas CotE drives outer coat assembly. SafA localizes to the cortex-coat interface. Both SafA and its short form C30 are substrates for Tgl, a coat-associated transglutaminase that cross-links proteins through ε-(γ-glutamyl)lysyl isopeptide bonds. We show that SafA and C30 are distributed between the coat and cortex layers. The deletion of tgl increases the extractability of SafA, mainly from the cortex. Tgl itself is mostly located in the inner coat and cortex. The localization of Tgl-cyan fluorescent protein (Tgl-CFP) is strongly, but not exclusively, dependent on safA However, the association of Tgl with the cortex requires safA Together, our results suggest an assembly pathway in which Tgl is first recruited to the forming spore in a manner that is only partially dependent on SafA and then is drafted to the cortex by SafA. Tgl, in turn, promotes the conversion of coat- and cortex-associated SafA into forms that resist extraction, possibly by catalyzing the cross-linking of SafA to other coat proteins, to the cortex, and/or to cortex-associated proteins. Therefore, the final assembly state of SafA relies on an autoregulatory pathway that requires the subcellular localization of a protein cross-linking enzyme. Tgl most likely exerts a "spotwelding" activity, cross-linking preformed complexes in the cortex and inner coat layers of spores.IMPORTANCE In this work, we show how two proteins work together to determine their subcellular location within the coat of bacterial endospores. Bacillus subtilis endospores are surrounded by a multilayer protein coat composed of over 80 proteins, which surrounds an underlying peptidoglycan layer (the spore cortex) protecting it from lytic enzymes. How specific coat proteins are targeted to specific layers of the coat is not well understood. We found that the protein SafA recruits a protein-cross-linking enzyme (a transglutaminase) to the cortex and inner layers of the coat, where both are cemented, by cross-linking, into macromolecular complexes.

The Spore Coat

Spores of Clostridiales and Bacillales are encased in a complex series of concentric shells that provide protection, facilitate germination, and mediate interactions with the environment. Analysis of diverse spore-forming species by thin-section transmission electron microscopy reveals that the number and morphology of these encasing shells vary greatly. In some species, they appear to be composed of a small number of discrete layers. In other species, they can comprise multiple, morphologically complex layers. In addition, spore surfaces can possess elaborate appendages. For all their variability, there is a consistent architecture to the layers encasing the spore. A hallmark of all Clostridiales and Bacillales spores is the cortex, a layer made of peptidoglycan. In close association with the cortex, all species examined possess, at a minimum, a series of proteinaceous layers, called the coat. In some species, including Bacillus subtilis, only the coat is present. In other species, including Bacillus anthracis, an additional layer, called the exosporium, surrounds the coat. Our goals here are to review the present understanding of the structure, composition, assembly, and functions of the coat, primarily in the model organism B. subtilis, but also in the small but growing number of other spore-forming species where new data are showing that there is much to be learned beyond the relatively well-developed basis of knowledge in B. subtilis. To help summarize this large field and define future directions for research, we will focus on key findings in recent years.

Sporulation Temperature Reveals a Requirement for CotE in the Assembly of both the Coat and Exosporium Layers of Bacillus cereus Spores

The Bacillus cereus spore surface layers consist of a coat surrounded by an exosporium. We investigated the interplay between the sporulation temperature and the CotE morphogenetic protein in the assembly of the surface layers of B. cereus ATCC 14579 spores and on the resulting spore properties. The cotE deletion affects the coat and exosporium composition of the spores formed both at the suboptimal temperature of 20°C and at the optimal growth temperature of 37°C. Transmission electron microscopy revealed that ΔcotE spores had a fragmented and detached exosporium when formed at 37°C. However, when produced at 20°C, ΔcotE spores showed defects in both coat and exosporium attachment and were susceptible to lysozyme and mutanolysin. Thus, CotE has a role in the assembly of both the coat and exosporium, which is more important during sporulation at 20°C. CotE was more represented in extracts from spores formed at 20°C than at 37°C, suggesting that increased synthesis of the protein is required to maintain proper assembly of spore surface layers at the former temperature. ΔcotE spores formed at either sporulation temperature were impaired in inosine-triggered germination and resistance to UV-C and H2O2 and were less hydrophobic than wild-type (WT) spores but had a higher resistance to wet heat. While underscoring the role of CotE in the assembly of B. cereus spore surface layers, our study also suggests a contribution of the protein to functional properties of additional spore structures. Moreover, it also suggests a complex relationship between the function of a spore morphogenetic protein and environmental factors such as the temperature during spore formation.

Protection of Bacillus pumilus spores by catalases

Bacillus pumilus SAFR-032, isolated at spacecraft assembly facilities of the National Aeronautics and Space Administration Jet Propulsion Laboratory, is difficult to kill by the sterilization method of choice, which uses liquid or vapor hydrogen peroxide. We identified two manganese catalases, YjqC and BPUM_1305, in spore protein extracts of several B. pumilus strains by using PAGE and mass spectrometric analyses. While the BPUM_1305 catalase was present in six of the B. pumilus strains tested, YjqC was not detected in ATCC 7061 and BG-B79. Furthermore, both catalases were localized in the spore coat layer along with laccase and superoxide dismutase. Although the initial catalase activity in ATCC 7061 spores was higher, it was less stable over time than the SAFR-032 enzyme. We propose that synergistic activity of YjqC and BPUM_1305, along with other coat oxidoreductases, contributes to the enhanced resistance of B. pumilus spores to hydrogen peroxide. We observed that the product of the catalase reaction, gaseous oxygen, forms expanding vesicles on the spore surface, affecting the mechanical integrity of the coat layer, resulting in aggregation of the spores. The accumulation of oxygen gas and aggregations may play a crucial role in limiting further exposure of Bacilli spore surfaces to hydrogen peroxide or other toxic chemicals when water is present.

Proteomic analysis of Bacillus thuringiensis strain 4.0718 at different growth phases

The growth process of Bacillus thuringiensis Bt4.0718 strain was studied using proteomic technologies. The proteins of Bt whole cells at three phases—middle vegetative, early sporulation, and late sporulation—were extracted with lysis buffer, followed with separation by 2-DE and identified by MALDI-TOF/TOF MS. Bioactive factors such as insecticidal crystal proteins (ICPs) including Cry1Ac(3), Cry2Aa, and BTRX28, immune inhibitor (InhA), and InhA precursor were identified. InhA started to express at the middle vegetative phase, suggesting its contribution to the survival of Bt in the host body. At the early sporulation phase, ICPs started their expression. CotJC, OppA, ORF1, and SpoIVA related to the formation of crystals and spores were identified, the expression characteristics of which ensured the stable formation of crystals and spores. This study provides an important foundation for further exploration of the stable expression of ICPs, the smooth formation of crystals, and the construction of recombinant strains.

Searching for protein-protein interactions within the Bacillus subtilis spore coat

The capability of endospores of Bacillus subtilis to withstand extreme environmental conditions is secured by several attributes. One of them, the protein shell that encases the spore and is known as the coat, provides the spore with its characteristic resistance to toxic chemicals, lytic enzymes, and predation by unicellular and multicellular eukaryotes. Despite most of the components of the spore coat having been identified, we have only a vague understanding of how such a complex structure is assembled. Using the yeast two-hybrid system, we attempted to identify direct contacts among the proteins allocated to the insoluble fraction of the spore coat: CotV, CotW, CotX, CotY, and CotZ. We also examined whether they could interact with CotE, one of the most crucial morphogenetic proteins governing outer coat formation and also present in the insoluble fraction. Out of all 21 possible interactions we tested, 4 were found to be positive. Among these interactions, we confirmed the previous observation that CotE forms homo-oligomers. In addition, we observed homotypic interactions of CotY, strong interactions between CotZ and CotY, and relatively weak, yet significant, interactions between CotV and CotW. The results of this yeast two-hybrid analysis were confirmed by size exclusion chromatography of recombinant coat proteins and a pull-down assay.

Characterization of spores of Bacillus subtilis that lack most coat layers

Spores of Bacillus subtilis have a thick outer layer of relatively insoluble protein called the coat, which protects spores against a number of treatments and may also play roles in spore germination. However, elucidation of precise roles of the coat in spore properties has been hampered by the inability to prepare spores lacking all or most coat material. In this work, we show that spores of a strain with mutations in both the cotE and gerE genes, which encode proteins involved in coat assembly and expression of genes encoding coat proteins, respectively, lack most extractable coat protein as seen by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, as well as the great majority of the coat as seen by atomic force microscopy. However, the cotE gerE spores did retain a thin layer of insoluble coat material that was most easily seen by microscopy following digestion of these spores with lysozyme. These severely coat-deficient spores germinated relatively normally with nutrients and even better with dodecylamine but not with a 1:1 chelate of Ca(2+) and dipicolinic acid. These spores were also quite resistant to wet heat, to mechanical disruption, and to treatment with detergents at an elevated temperature and pH but were exquisitely sensitive to killing by sodium hypochlorite. These results provide new insight into the role of the coat layer in spore properties.

Auto-induction and purification of a Bacillus subtilis transglutaminase (Tgl) and its preliminary crystallographic characterization

Spores of Bacillus subtilis are covered by a multi-protein protective coat which is a key factor in their extreme environmental resilience. A fraction of the coat proteins undergoes covalent cross-linking following their assembly at the spore surface. Several types of covalent cross-links are found in the coat. These include epsilon-(gamma-glutamyl)lysine bonds whose formation is catalyzed by a transglutaminase, Tgl, itself a coat component. Tgl is the smallest known transglutaminase. It bears no sequence resemblance to other proteins in databases, except for its counterparts in other Bacillus and related species, suggesting a highly specialized role in coat assembly. It is not known to what degree are the Tgl-like proteins structural and mechanistically related to other transglutaminases. Here, we have fused the His(6) tag to the C-terminal end of Tgl, and shown that the fusion protein is functional in vivo. We have overproduced B. subtilis Tgl-His(6) by auto-induction with high yield and purified the protein to nearly homogeneity in a single chromatographic step. The purified protein, active as it catalyzed the cross-linking of bovine serum albumin, behaved as a monomer of about 33kDa in solution. Lastly, Tgl was crystallized and X-ray diffraction data were collected using synchrotron radiation to 2.1A resolution. Crystals of Tgl belong to the tetragonal space group P4(1,3) and contain two molecules per asymmetric unit.

Structure, assembly, and function of the spore surface layers

Endospores formed by Bacillus, Clostridia, and related genera are encased in a protein shell called the coat. In many species, including B. subtilis, the coat is the outermost spore structure, and in other species, such as the pathogenic organisms B. anthracis and B. cereus, the spore is encased in an additional layer called the exosporium. Both the coat and the exosporium have roles in protection of the spore and in its environmental interactions. Assembly of both structures is a function of the mother cell, one of two cellular compartments of the developing sporangium. Studies in B. subtilis have revealed that the timing of coat protein production, the guiding role of a small group of morphogenetic proteins, and several types of posttranslational modifications are essential for the fidelity of the assembly process. Assembly of the exosporium requires a set of novel proteins as well as homologues of proteins found in the outermost layers of the coat and of some of the coat morphogenetic factors, suggesting that the exosporium is a more specialized structure of a multifunctional coat. These and other insights into the molecular details of spore surface morphogenesis provide avenues for exploitation of the spore surface layers in applications for biotechnology and medicine.

Determinants for the subcellular localization and function of a nonessential SEDS protein

The Bacillus subtilis SpoVE integral membrane protein is essential for the heat resistance of spores, probably because of its involvement in spore peptidoglycan synthesis. We found that an SpoVE-yellow fluorescent protein (YFP) fusion protein becomes localized to the forespore during the earliest stages of engulfment, and this pattern is maintained throughout sporulation. SpoVE belongs to a well-conserved family of proteins that includes the FtsW and RodA proteins of B. subtilis. These proteins are involved in bacterial shape determination, although their function is not known. FtsW is necessary for the formation of the asymmetric septum in sporulation, and we found that an FtsW-YFP fusion localized to this structure prior to the initiation of engulfment in a nonoverlapping pattern with SpoVE-cyan fluorescent protein. Since FtsW and RodA are essential for normal growth, it has not been possible to identify loss-of-function mutations that would greatly facilitate analysis of their function. We took advantage of the fact that SpoVE is not required for growth to obtain point mutations in SpoVE that block the development of spore heat resistance but that allow normal protein expression and targeting to the forespore. These mutant proteins will be invaluable tools for future experiments aimed at elucidating the function of members of the SEDS ("shape, elongation, division, and sporulation") family of proteins.

The timing of cotE expression affects Bacillus subtilis spore coat morphology but not lysozyme resistance

The synthesis of structural components and morphogenetic factors required for the assembly of the Bacillus subtilis spore coat is governed by a mother cell-specific transcriptional cascade. The first two temporal classes of gene expression, which involve RNA polymerase sigma sigma(E) factor and the ancillary regulators GerR and SpoIIID, are deployed prior to engulfment of the prespore by the mother cell. The two last classes rely on sigma(K), whose activation follows engulfment completion, and GerE. The cotE gene codes for a morphogenetic protein essential for the assembly of the outer coat layer and spore resistance to lysozyme. cotE is expressed first from a sigma(E)-dependent promoter and, in a second stage, from a promoter that additionally requires SpoIIID and that remains active under sigma(K) control. CotE localizes prior to engulfment completion close to the surface of the developing spore, but formation of the outer coat is a late, sigma(K)-controlled event. We have transplanted cotE to progressively later classes of mother cell gene expression. This created an early class of mutants in which cotE is expressed prior to engulfment completion and a late class in which expression of cotE follows the complete engulfment of the prespore. Mutants of the early class assemble a nearly normal outer coat structure, whereas mutants of the late class do not. Hence, the early expression of CotE is essential for outer coat assembly. Surprisingly, however, all mutants were fully resistant to lysozyme. The results suggest that CotE has genetically separable functions in spore resistance to lysozyme and spore outer coat assembly.

Interaction between coat morphogenetic proteins SafA and SpoVID

Morphogenetic proteins such as SpoVID and SafA govern assembly of the Bacillus subtilis endospore coat by guiding the various protein structural components to the surface of the developing spore. Previously, a screen for peptides able to interact with SpoVID led to the identification of a PYYH motif present in the C-terminal half of the SafA protein and to the subsequent demonstration that SpoVID and SafA directly interact. spoVID and safA spores show deficiencies in coat assembly and are lysozyme susceptible. Both proteins, orthologs of which are found in all Bacillus species, have LysM domains for peptidoglycan binding and localize to the cortex-coat interface. Here, we show that the interaction between SafA and SpoVID involves the PYYH motif (region B) but also a 13-amino-acid region (region A) just downstream of the N-terminal LysM domain of SafA. We show that deletion of region B does not block the interaction of SafA with SpoVID, nor does it bring about spore susceptibility to lysozyme. Nevertheless, it appears to reduce the interaction and affects the complex. In contrast, lesions in region A impaired the interaction of SafA with SpoVID in vitro and, while not affecting the accumulation of SafA in vivo, interfered with the localization of SafA around the developing spore, causing aberrant assembly of the coat and lysozyme sensitivity. A peptide corresponding to region A interacts with SpoVID, suggesting that residues within this region directly contact SpoVID. Since region A is highly conserved among SafA orthologs, this motif may be an important determinant of coat assembly in the group of Bacillus spore formers.

Localization of the Bacillus subtilis murB gene within the dcw cluster is important for growth and sporulation

The Bacillus subtilis murB gene, encoding UDP-N-acetylenolpyruvoylglucosamine reductase, a key enzyme in the peptidoglycan (PG) biosynthetic pathway, is embedded in the dcw (for "division and cell wall") cluster immediately upstream of divIB. Previous attempts to inactivate murB were unsuccessful, suggesting its essentiality. Here we show that the cell morphology, growth rate, and resistance to cell wall-active antibiotics of murB conditional mutants is a function of the expression level of murB. In one mutant, in which murB was insertionally inactivated in a merodiploid bearing a second xylose-inducible PxylA-murB allele, DivIB levels were reduced and a normal growth rate was achieved only if MurB levels were threefold that of the wild-type strain. However, expression of an extra copy of divIB restored normal growth at wild-type levels of MurB. In contrast, DivIB levels were normal in a second mutant containing an in-frame deletion of murB (DeltamurB) in the presence of the PxylA-murB gene. Furthermore, this strain grew normally with wild-type levels of MurB. During sporulation, the levels of MurB were highest at the time of synthesis of the spore cortex PG. Interestingly, the DeltamurB PxylA-murB mutant did not sporulate efficiently even at high concentrations of inducer. Since high levels of inducer did not interfere with sporulation of a murB(+)PxylA-murB strain, it appears that ectopic expression of murB fails to support efficient sporulation. These data suggest that coordinate expression of divIB and murB is important for growth and sporulation. The genetic context of the murB gene within the dcw cluster is unique to the Bacillus group and, taken together with our data, suggests that in these species it contributes to the optimal expression of cell division and PG biosynthetic functions during both vegetative growth and spore development.

TheBacillus subtilisspore coat protein interaction network

Bacterial spores are surrounded by a morphologically complex, mechanically flexible protein coat, which protects the spore from toxic molecules. The interactions among the over 50 proteins that make up the coat remain poorly understood. We have used cell biological and protein biochemical approaches to identify novel coat proteins in Bacillus subtilis and describe the network of their interactions, in order to understand coat assembly and the molecular basis of its protective functions and mechanical properties. Our analysis characterizes the interactions between 32 coat proteins. This detailed view reveals a complex interaction network. A key feature of the network is the importance of a small subset of proteins that direct the assembly of most of the coat. From an analysis of the network topology, we propose a model in which low-affinity interactions are abundant in the coat and account, to a significant degree, for the coat's mechanical properties as well as structural variation between spores.

Interactions among CotB, CotG, and CotH during assembly of the Bacillus subtilis spore coat

Spores formed by wild-type Bacillus subtilis are encased in a multilayered protein structure (called the coat) formed by the ordered assembly of over 30 polypeptides. One polypeptide (CotB) is a surface-exposed coat component that has been used as a vehicle for the display of heterologous antigens at the spore surface. The cotB gene was initially identified by reverse genetics as encoding an abundant coat component. cotB is predicted to code for a 43-kDa polypeptide, but the form that prevails in the spore coat has a molecular mass of about 66 kDa (herein designated CotB-66). Here we show that in good agreement with its predicted size, expression of cotB in Escherichia coli results in the accumulation of a 46-kDa protein (CotB-46). Expression of cotB in sporulating cells of B. subtilis also results in a 46-kDa polypeptide which appears to be rapidly converted into CotB-66. These results suggest that soon after synthesis, CotB undergoes a posttranslational modification. Assembly of CotB-66 has been shown to depend on expression of both the cotH and cotG loci. We found that CotB-46 is the predominant form found in extracts prepared from sporulating cells or in spore coat preparations of cotH or cotG mutants. Therefore, both cotH and cotG are required for the efficient conversion of CotB-46 into CotB-66 but are dispensable for the association of CotB-46 with the spore coat. We also show that CotG does not accumulate in sporulating cells of a cotH mutant, suggesting that CotH (or a CotH-controlled factor) stabilizes the otherwise unstable CotG. Thus, the need for CotH for formation of CotB-66 results in part from its role in the stabilization of CotG. We also found that CotB-46 is present in complexes with CotG at the time when formation of CotB-66 is detected. Moreover, using a yeast two-hybrid system, we found evidence that CotB directly interacts with CotG and that both CotB and CotG self-interact. We suggest that an interaction between CotG and CotB is required for the formation of CotB-66, which may represent a multimeric form of CotB.

Formation and composition of the Bacillus anthracis endospore

The endospores of Bacillus anthracis are the infectious particles of anthrax. Spores are dormant bacterial morphotypes able to withstand harsh environments for decades, which contributes to their ability to be formulated and dispersed as a biological weapon. We monitored gene expression in B. anthracis during growth and sporulation using full genome DNA microarrays and matched the results against a comprehensive analysis of the mature anthrax spore proteome. A large portion (approximately 36%) of the B. anthracis genome is regulated in a growth phase-dependent manner, and this regulation is marked by five distinct waves of gene expression as cells proceed from exponential growth through sporulation. The identities of more than 750 proteins present in the spore were determined by multidimensional chromatography and tandem mass spectrometry. Comparison of data sets revealed that while the genes responsible for assembly and maturation of the spore are tightly regulated in discrete stages, many of the components ultimately found in the spore are expressed throughout and even before sporulation, suggesting that gene expression during sporulation may be mainly related to the physical construction of the spore, rather than synthesis of eventual spore content. The spore also contains an assortment of specialized, but not obviously related, metabolic and protective proteins. These findings contribute to our understanding of spore formation and function and will be useful in the detection, prevention, and early treatment of anthrax. This study also highlights the complementary nature of genomic and proteomic analyses and the benefits of combining these approaches in a single study.

Crystal structure of a bacterial endospore coat component. A laccase with enhanced thermostability properties

Endospores produced by the Gram-positive soil bacterium Bacillus subtilis are shielded by a proteinaceous coat formed by over 30 structural components, which self-assemble into a lamellar inner coat and a thicker striated electrodense outer coat. The 65-kDa CotA protein is an abundant component of the outer coat layer. CotA is a highly thermostable laccase, assembly of which into the coat is required for spore resistance against hydrogen peroxide and UV light. Here, we report the structure of CotA at 1.7-A resolution, as determined by x-ray crystallography. This is the first structure of an endospore coat component, and also the first structure of a bacterial laccase. The overall fold of CotA comprises three cupredoxin-like domains and includes one mononuclear and one trinuclear copper center. This arrangement is similar to that of other multicopper oxidases and most similar to that of the copper tolerance protein CueO of Escherichia coli. However, the three cupredoxin domains in CotA are further linked by external interdomain loops, which increase the packing level of the structure. We propose that these interdomain loops contribute to the remarkable thermostability of the enzyme, but our results suggest that additional factors are likely to play a role. Comparisons with the structure of other monomeric multicopper oxidases containing four copper atoms suggest that CotA may accept the largest substrates of any known laccase. Moreover, and unlike other laccases, CotA appears to have a flexible lidlike region close to the substrate-binding site that may mediate substrate accessibility. The implications of these findings for the properties of CotA, its assembly and the properties of the bacterial spore coat structure are discussed.

Proteomic analysis of the spore coats of Bacillus subtilis and Bacillus anthracis

The outermost proteinaceous layer of bacterial spores, called the coat, is critical for spore survival, germination, and, for pathogenic spores, disease. To identify novel spore coat proteins, we have carried out a preliminary proteomic analysis of Bacillus subtilis and Bacillus anthracis spores, using a combination of standard sodium dodecyl sulfate-polyacrylamide gel electrophoresis separation and improved two-dimensional electrophoretic separations, followed by matrix-assisted laser desorption ionization-time of flight and/or dual mass spectrometry. We identified 38 B. subtilis spore proteins, 12 of which are known coat proteins. We propose that, of the novel proteins, YtaA, YvdP, and YnzH are bona fide coat proteins, and we have renamed them CotI, CotQ, and CotU, respectively. In addition, we initiated a study of coat proteins in B. anthracis and identified 11 spore proteins, 6 of which are candidate coat or exosporium proteins. We also queried the unfinished B. anthracis genome for potential coat proteins. Our analysis suggests that the B. subtilis and B. anthracis coats have roughly similar numbers of proteins and that a core group of coat protein species is shared between these organisms, including the major morphogenetic proteins. Nonetheless, a significant number of coat proteins are probably unique to each species. These results should accelerate efforts to develop B. anthracis detection methods and understand the ecological role of the coat.

Proteomics characterization of novel spore proteins of Bacillus subtilis

The spores of Bacillus subtilis have characteristic properties and consist of complex structures including various types of proteins. To perform comprehensive analysis of the protein composition of the spores, the proteins extracted from the spore were analysed by a combination of one-dimensional PAGE and liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) using Turboquest SEQUEST software interfaced with the DNA sequence database of B. subtilis. A total of 154 proteins were identified, and 69 of them were novel. The remaining 85 proteins have been previously reported as sporulation-specific proteins or as proteins that are synthesized in vegetative cells. The expression pattern of each gene deduced to encode novel spore proteins was analysed using a series of strains carrying a lacZ reporter gene. The results revealed that the expression of 26 genes was dependent on sporulation-specific sigma factors, namely sigma(F), sigma(E), sigma(G) and sigma(K). In this study, it is demonstrated that the combination of the techniques of SDS-PAGE and LC-MS/MS, with the mutant library of B. subtilis, is an effective tool for the analysis of complicated cellular structures.

Molecular and biochemical characterization of a highly stable bacterial laccase that occurs as a structural component of the Bacillus subtilis endospore coat

The Bacillus subtilis endospore coat protein CotA shows laccase activity. By using comparative modeling techniques, we were able to derive a model for CotA based on the known x-ray structures of zucchini ascorbate oxidase and Cuprinus cereneus laccase. This model of CotA contains all the structural features of a laccase, including the reactive surface-exposed copper center (T1) and two buried copper centers (T2 and T3). Single amino acid substitutions in the CotA T1 copper center (H497A, or M502L) did not prevent assembly of the mutant proteins into the coat and did not alter the pattern of extractable coat polypeptides. However, in contrast to a wild type strain, both mutants produced unpigmented colonies and spores unable to oxidize syringaldazine (SGZ) and 2'2-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS). The CotA protein was purified to homogeneity from an overproducing Escherichia coli strain. The purified CotA shows an absorbance and a EPR spectra typical of blue multicopper oxidases. Optimal enzymatic activity was found at < or =pH 3.0 and at pH 7.0 for ABTS or SGZ oxidation, respectively. The apparent K(m) values for ABTS and SGZ at 37 degrees C were of 106 +/- 11 and 26 +/- 2 microm, respectively, with corresponding k(cat) values of 16.8 +/- 0.8 and 3.7 +/- 0.1 s(-1). Maximal enzyme activity was observed at 75 degrees C with ABTS as substrate. Remarkably, the coat-associated or the purified enzyme showed a half-life of inactivation at 80 degrees C of about 4 and 2 h, respectively, indicating that CotA is intrinsically highly thermostable.

Localization of the cortex lytic enzyme CwlJ in spores of Bacillus subtilis

The enzyme CwlJ is involved in the depolymerization of cortex peptidoglycan during germination of spores of Bacillus subtilis. CwlJ with a C-terminal His tag was functional and was extracted from spores by procedures that remove spore coat proteins. However, this CwlJ was not extracted from disrupted spores by dilute buffer, high salt concentrations, Triton X-100, Ca(2+)-dipicolinic acid, dithiothreitol, or peptidoglycan digestion, disappeared during spore germination, and was not present in cotE spores in which the spore coat is aberrant. These findings indicate the following: (i) the reason decoated and cotE spores germinate poorly with dipicolinic acid is the absence of CwlJ from these spores; and (ii) CwlJ is located in the spore coat, presumably tightly associated with one or more other coat proteins.

Functional analysis of the Bacillus subtilis morphogenetic spore coat protein CotE

Bacterial spores are surrounded by a multilayered proteinaceous shell called the coat. In Bacillus subtilis, a coat protein called CotE guides the assembly of a major subset of coat proteins. To understand how CotE carries out its role in coat morphogenesis, we subjected its gene to mutagenesis and studied the effects of altered versions of CotE on coat formation. We identified regions within the C-terminal 28 amino acids that direct the deposition of the coat proteins CotA, CotB, CotG, CotSA, CotS and 35 kDa and 49 kDa proteins likely to be the spore proteins CotR (formerly known as YvdO) and YaaH respectively. The timing and genetic dependency of CotR accumulation are consistent with control of its gene by sigmaK and GerE. In addition, we identified a 35-amino-acid internal region involved in targeting of CotE to the forespore. Finally, we found that sequences within this 35-amino-acid region as well as within an 18-amino-acid stretch in the N-terminus of CotE direct the formation of CotE multimers, most probably homooligomers. These results suggest that: (i) most interactions between CotE and the coat proteins assembled under CotE control take place at the CotE C-terminus; (ii) an internal region of CotE connects it with the forespore surface; and (iii) interactions between CotE molecules depend on residues within an 18-amino-acid region in the N-terminal half of CotE.

Crystal structure of manganese catalase from Lactobacillus plantarum

BACKGROUND

Catalases are important antioxidant metalloenzymes that catalyze disproportionation of hydrogen peroxide, forming dioxygen and water. Two families of catalases are known, one having a heme cofactor, and the other, a structurally distinct family containing nonheme manganese. We have solved the structure of the mesophilic manganese catalase from Lactobacillus plantarum and its azide-inhibited complex.

RESULTS

The crystal structure of the native enzyme has been solved at 1.8 A resolution by molecular replacement, and the azide complex of the native protein has been solved at 1.4 A resolution. The hexameric structure of the holoenzyme is stabilized by extensive intersubunit contacts, including a beta zipper and a structural calcium ion crosslinking neighboring subunits. Each subunit contains a dimanganese active site, accessed by a single substrate channel lined by charged residues. The manganese ions are linked by a mu1,3-bridging glutamate carboxylate and two mu-bridging solvent oxygens that electronically couple the metal centers. The active site region includes two residues (Arg147 and Glu178) that appear to be unique to the Lactobacillus plantarum catalase.

CONCLUSIONS

A comparison of L. plantarum and T. thermophilus catalase structures reveals the existence of two distinct structural classes, differing in monomer design and the organization of their active sites, within the manganese catalase family. These differences have important implications for catalysis and may reflect distinct biological functions for the two enzymes, with the L. plantarum enzyme serving as a catalase, while the T. thermophilus enzyme may function as a catalase/peroxidase.

SpoVID guides SafA to the spore coat in Bacillus subtilis

Bacteria assemble complex structures by targeting proteins to specific subcellular locations. The protein coat that encases Bacillus subtilis spores is an example of a structure that requires coordinated targeting and assembly of more than 24 polypeptides. The earliest stages of coat assembly require the action of three morphogenetic proteins: SpoIVA, CotE, and SpoVID. In the first steps, a basement layer of SpoIVA forms around the surface of the forespore, guiding the subsequent positioning of a ring of CotE protein about 75 nm from the forespore surface. SpoVID localizes near the forespore membrane where it functions to maintain the integrity of the CotE ring and to anchor the nascent coat to the underlying spore structures. However, it is not known which spore coat proteins interact directly with SpoVID. In this study we examined the interaction between SpoVID and another spore coat protein, SafA, in vivo using the yeast two-hybrid system and in vitro. We found evidence that SpoVID and SafA directly interact and that SafA interacts with itself. Immunofluorescence microscopy showed that SafA localized around the forespore early during coat assembly and that this localization of SafA was dependent on SpoVID. Moreover, targeting of SafA to the forespore was also dependent on SpoIVA, as was targeting of SpoVID to the forespore. We suggest that the localization of SafA to the spore coat requires direct interaction with SpoVID.

Investigation of bacterial spore structure by high resolution solid-state nuclear magnetic resonance spectroscopy and transmission electron microscopy

High resolution solid-state nuclear magnetic resonance spectroscopy (NMR) in combination with transmission electron microscopy (TEM) of spores of Bacillus cereus, an outer coatless mutant B. subtilis 322, an inner coatless mutant B. subtilis 325 and of germinated spores of B. subtilis CMCC 604 were carried out. Structural differences in the coats, mainly protein of spores were reflected by NMR spectra which indicated also differences in molecular mobility of carbohydrates which was partially attributed to the cortex. Dipicolinic acid (DPA) of spores of B. cereus displayed a high degree of solid state order and may be crystalline. Heat activation was studied on spores of B. subtilis 357 lux + and revealed a structural change when analysed by TEM but this was not associated with increases in molecular mobility since no effects were measured by NMR.

Morphogenetic proteins SpoVID and SafA form a complex during assembly of the Bacillus subtilis spore coat

During endospore formation in Bacillus subtilis, over two dozen polypeptides are assembled into a multilayered structure known as the spore coat, which protects the cortex peptidoglycan (PG) and permits efficient germination. In the initial stages of coat assembly a protein known as CotE forms a ring around the forespore. A second morphogenetic protein, SpoVID, is required for maintenance of the CotE ring during the later stages, when most of proteins are assembled into the coat. Here, we report on a protein that appears to associate with SpoVID during the early stage of coat assembly. This protein, which we call SafA for SpoVID-associated factor A, is encoded by a locus previously known as yrbA. We confirmed the results of a previous study that showed safA mutant spores have defective coats which are missing several proteins. We have extended these studies with the finding that SafA and SpoVID were coimmunoprecipitated by anti-SafA or anti-SpoVID antiserum from whole-cell extracts 3 and 4 h after the onset of sporulation. Therefore, SafA may associate with SpoVID during the early stage of coat assembly. We used immunogold electron microscopy to localize SafA and found it in the cortex, near the interface with the coat in mature spores. SafA appears to have a modular design. The C-terminal region of SafA is similar to those of several inner spore coat proteins. The N-terminal region contains a sequence that is conserved among proteins that associate with the cell wall. This motif in the N-terminal region may target SafA to the PG-containing regions of the developing spore.

Role of the spore coat layers in Bacillus subtilis spore resistance to hydrogen peroxide, artificial UV-C, UV-B, and solar UV radiation

Spores of Bacillus subtilis possess a thick protein coat that consists of an electron-dense outer coat layer and a lamellalike inner coat layer. The spore coat has been shown to confer resistance to lysozyme and other sporicidal substances. In this study, spore coat-defective mutants of B. subtilis (containing the gerE36 and/or cotE::cat mutation) were used to study the relative contributions of spore coat layers to spore resistance to hydrogen peroxide (H(2)O(2)) and various artificial and solar UV treatments. Spores of strains carrying mutations in gerE and/or cotE were very sensitive to lysozyme and to 5% H(2)O(2), as were chemically decoated spores of the wild-type parental strain. Spores of all coat-defective strains were as resistant to 254-nm UV-C radiation as wild-type spores were. Spores possessing the gerE36 mutation were significantly more sensitive to artificial UV-B and solar UV radiation than wild-type spores were. In contrast, spores of strains possessing the cotE::cat mutation were significantly more resistant to all of the UV treatments used than wild-type spores were. Spores of strains carrying both the gerE36 and cotE::cat mutations behaved like gerE36 mutant spores. Our results indicate that the spore coat, particularly the inner coat layer, plays a role in spore resistance to environmentally relevant UV wavelengths.

Structure and assembly of the bacterial endospore coat

Many biological processes are mediated through the action of multiprotein complexes, often assembled at specific cellular locations. Bacterial endospores for example, are encased in a proteinaceous coat, which confers resistance to lysozyme and harsh chemicals and influences the spore response to germinants. In Bacillus subtilis, the coat is composed of more than 20 polypeptides, organized into three main layers: an amorphous undercoat; a lamellar, lightly staining inner structure; and closely apposed to it, a striated electron-dense outer coat. Synthesis of the coat proteins is temporally and spatially governed by a cascade of four mother cell-specific transcription factors. However, the order of assembly and final destination of the coat structural components may rely mainly on specific protein-protein interactions, as well as on the action of accessory morphogenetic proteins. Proteolytic events, protein-protein crosslinking, and protein glycosylation also play a role in the assembly process. These modifications are carried out by enzymes that may themselves be targeted to the coat layers. Coat genes have been identified by reverse genetics or, more recently, by screens for mother cell-specific promoters or for peptide sequences able to interact with certain bait proteins. A role for a given locus in coat assembly is established by a combination of regulatory, functional, morphological, and topological criteria. Because of the amenability of B. subtilis to genetic analysis (now facilitated by the knowledge of its genome sequence), coat formation has become an attractive model for the assembly of complex macromolecular structures during development.

A Bacillus subtilis secreted protein with a role in endospore coat assembly and function

Bacterial endospores are encased in a complex protein coat, which confers protection against noxious chemicals and influences the germination response. In Bacillus subtilis, over 20 polypeptides are organized into an amorphous undercoat, a lamellar lightly staining inner structure, and an electron-dense outer coat. Here we report on the identification of a polypeptide of about 30 kDa required for proper coat assembly, which was extracted from spores of a gerE mutant. The N-terminal sequence of this polypeptide matched the deduced product of the tasA gene, after removal of a putative 27-residue signal peptide, and TasA was immunologically detected in material extracted from purified spores. Remarkably, deletion of tasA results in the production of asymmetric spores that accumulate misassembled material in one pole and have a greatly expanded undercoat and an altered outer coat structure. Moreover, we found that tasA and gerE mutations act synergistically to decrease the efficiency of spore germination. We show that tasA is the most distal member of a three-gene operon, which also encodes the type I signal peptidase SipW. Expression of the tasA operon is enhanced 2 h after the onset of sporulation, under the control of sigmaH. When tasA transcription is uncoupled from sipW expression, a presumptive TasA precursor accumulates, suggesting that its maturation depends on SipW. Mature TasA is found in supernatants of sporulating cultures and intracellularly from 2 h of sporulation onward. We suggest that, at an early stage of sporulation, TasA is secreted to the septal compartment. Later, after engulfment of the prespore by the mother cell, TasA acts from the septal-proximal pole of the spore membranes to nucleate the organization of the undercoat region. TasA is the first example of a polypeptide involved in coat assembly whose production is not mother cell specific but rather precedes its formation. Our results implicate secretion as a mechanism to target individual proteins to specific cellular locations during the assembly of the bacterial endospore coat.

Assembly of the CotSA coat protein into spores requires CotS in Bacillus subtilis

The CotSA protein, encoded by cotSA (ytxN) of Bacillus subtilis, was detected from the cells at 5 h after the onset of sporulation (T5) and in the spore coat of wild-type cells, but not in cotE, cotS, gerE, or cotSA mutant spores. CotSA was also detected in the sporangium at T5 to T7 but not in the sporangium at T18 of cotS mutant cells, while the incorporation of CotS into the coat was not dependent upon CotSA. These results suggested that CotSA was synthesized simultaneously with CotS during T5 to T7 of sporulation and assembled into the coat dependent upon CotS.

Bacillus subtilis spore coat

In response to starvation, bacilli and clostridia undergo a specialized program of development that results in the production of a highly resistant dormant cell type known as the spore. A proteinacious shell, called the coat, encases the spore and plays a major role in spore survival. The coat is composed of over 25 polypeptide species, organized into several morphologically distinct layers. The mechanisms that guide coat assembly have been largely unknown until recently. We now know that proper formation of the coat relies on the genetic program that guides the synthesis of spore components during development as well as on morphogenetic proteins dedicated to coat assembly. Over 20 structural and morphogenetic genes have been cloned. In this review, we consider the contributions of the known coat and morphogenetic proteins to coat function and assembly. We present a model that describes how morphogenetic proteins direct coat assembly to the specific subcellular site of the nascent spore surface and how they establish the coat layers. We also discuss the importance of posttranslational processing of coat proteins in coat morphogenesis. Finally, we review some of the major outstanding questions in the field.

Involvement of superoxide dismutase in spore coat assembly in Bacillus subtilis

Endospores of Bacillus subtilis are enclosed in a proteinaceous coat which can be differentiated into a thick, striated outer layer and a thinner, lamellar inner layer. We found that the N-terminal sequence of a 25-kDa protein present in a preparation of spore coat proteins matched that of the Mn-dependent superoxide dismutase (SOD) encoded by the sod4 locus. sod4 is transcribed throughout the growth and sporulation of a wild-type strain and is responsible for the SOD activity detected in total cell extracts prepared from B. subtilis. Disruption of the sod4 locus produced a mutant that lacked any detectable SOD activity during vegetative growth and sporulation. The sodA mutant was not impaired in the ability to form heat- or lysozyme-resistant spores. However, examination of the coat layers of sodA mutant spores revealed increased extractability of the tyrosine-rich outer coat protein CotG. We showed that this condition was not accompanied by augmented transcription of the cotG gene in sporulating cells of the sodA mutant. We conclude that SodA is required for the assembly of CotG into the insoluble matrix of the spore and suggest that CotG is covalently cross-linked into the insoluble matrix by an oxidative reaction dependent on SodA. Ultrastructural analysis revealed that the inner coat formed by a sodA mutant was incomplete. Moreover, the outer coat lacked the characteristic striated appearance of wild-type spores, a pattern that was accentuated in a cotG mutant. These observations suggest that the SodA-dependent formation of the insoluble matrix containing CotG is largely responsible for the striated appearance of this coat layer.