Levels of small molecules and enzymes in the mother cell compartment and the forespore of sporulating Bacillus megaterium

Spore germination and lactic acid combined treatment: A new processing strategy for the shelf-life extension of instant wet noodles

Bacillus amyloliquefaciens (BAM) was identified as the predominant spoilage bacteria in instant wet noodles (IWNs). The utilization of industrial acid treatment as a long shelf-life strategy resulted in reduced consumer acceptance due to the acidic taste of the products. This study proposed a processing strategy that integrated spore germination (SG) and lactic acid (LA) treatment to effectively reduce the spore survival rate and extend the shelf life of IWNs. L-histidine, d-glucose, and sodium chloride were highly efficient and safe germinants for BAM spores. In IWNs, compound germinants (1.0 % L-histidine, 0.5 % d-glucose, and 1.0 % sodium chloride) boosted the SG rate by 3.61 times. With synergistic LA treatment, the spore lethality increased by 34.41 % -41.68 %. Under the SG and reduced acid-heat conditions of pH 2.30-2.50, the mortality of spores could reach 92.00 %-93.17 %, which was 14.11 %-15.28 % higher than the industrial acid-heat condition of pH 2.10. DPA, ATP, and membrane potential showed that germinants reduced the spore membrane permeability and promoted the occurrence of spore membrane damage under acid-heat conditions. Moreover, this strategy significantly extended the shelf-life of IWNs by 3.00-5.50 times and controlled the pH ≥ 5.50. Additionally, it improved color, texture, and overall sensory evaluation. Accordingly, this strategy solved the contradiction between the long shelf-life of IWNs and the unacceptable acidification in industrial production.

Sporulation, Structure Assembly, and Germination in the Soil Bacterium Bacillus thuringiensis: Survival and Success in the Environment and the Insect Host

Bacillus thuringiensis (Bt) is a rod-shaped, Gram-positive soil bacterium that belongs to the phylum Firmicutes and the genus Bacillus. It is a spore-forming bacterium. During sporulation, it produces a wide range of crystalline proteins that are toxic to different orders of insects. Sporulation, structure assembly, and germination are essential stages in the cell cycle of B. thuringiensis. The majority of studies on these issues have focused on the model organism Bacillus subtilis, followed by Bacillus cereus and Bacillus anthracis. The machinery for sporulation and germination extrapolated to B. thuringiensis. However, in the light of recent findings concerning the role of the sporulation proteins (SPoVS), the germination receptors (Gr), and the cortical enzymes in Bt, the theory strengthened that conservation in sporulation, structure assembly, and germination programs drive the survival and success of B. thuringiensis in the environment and the insect host. In the present minireview, the latter pinpointed and reviewed.

Levels and Characteristics of mRNAs in Spores of Firmicute Species

Spores of firmicute species contain 100s of mRNAs, whose major function in Bacillus subtilis is to provide ribonucleotides for new RNA synthesis when spores germinate. To determine if this is a general phenomenon, RNA was isolated from spores of multiple firmicute species and relative mRNA levels determined by transcriptome sequencing (RNA-seq). Determination of RNA levels in single spores allowed calculation of RNA nucleotides/spore, and assuming mRNA is 3% of spore RNA indicated that only ∼6% of spore mRNAs were present at >1/spore. Bacillus subtilis, Bacillus atrophaeus, and Clostridioides difficile spores had 49, 42, and 51 mRNAs at >1/spore, and numbers of mRNAs at ≥1/spore were ∼10 to 50% higher in Geobacillus stearothermophilus and Bacillus thuringiensis Al Hakam spores and ∼4-fold higher in Bacillus megaterium spores. In all species, some to many abundant spore mRNAs (i) were transcribed by RNA polymerase with forespore-specific σ factors, (ii) encoded proteins that were homologs of those encoded by abundant B. subtilis spore mRNAs and are proteins in dormant spores, and (iii) were likely transcribed in the mother cell compartment of the sporulating cell. Analysis of the coverage of RNA-seq reads on mRNAs from all species suggested that abundant spore mRNAs were fragmented, as was confirmed by reverse transcriptase quantitative PCR (RT-qPCR) analysis of abundant B. subtilis and C. difficile spore mRNAs. These data add to evidence indicating that the function of at least the great majority of mRNAs in all firmicute spores is to be degraded to generate ribonucleotides for new RNA synthesis when spores germinate. IMPORTANCE Only ∼6% of mRNAs in spores of six firmicute species are at ≥1 molecule/spore, many abundant spore mRNAs encode proteins similar to B. subtilis spore proteins, and some abundant B. subtilis and C. difficile spore mRNAs were fragmented. Most of the abundant B. subtilis and other Bacillales spore mRNAs are transcribed under the control of the forespore-specific RNA polymerase σ factors, F or G, and these results may stimulate transcription analyses in developing spores of species other than B. subtilis. These findings, plus the absence of key nucleotide biosynthetic enzymes in spores, suggest that firmicute spores' abundant mRNAs are not translated when spores germinate but instead are degraded to generate ribonucleotides for new RNA synthesis by the germinated spore.

Bioluminescence dynamics in single germinating bacterial spores reveal metabolic heterogeneity

Spore-forming bacteria modulate their metabolic rate by over five orders of magnitude as they transition between dormant spores and vegetative cells and thus represent an extreme case of phenotypic variation. During environmental changes in nutrient availability, clonal populations of spore-forming bacteria exhibit individual differences in cell fate, the timing of phenotypic transitions and gene expression. One potential source of this variability is metabolic heterogeneity, but this has not yet been measured, as existing single-cell methods are not easily applicable to spores due to their small size and strong autofluorescence. Here, we use the bacterial bioluminescence system and a highly sensitive microscope to measure metabolic dynamics in thousands of B. subtilis spores as they germinate. We observe and quantitate large variations in the bioluminescence dynamics across individual spores that can be decomposed into contributions from variability in germination timing, the amount of endogenously produced luminescence substrate and the intracellular reducing power. This work shows that quantitative measurement of spore metabolism is possible and thus it opens avenues for future study of the thermodynamic nature of dormant states.

Channels modestly impact compartment-specific ATP levels during Bacillus subtilis sporulation and a rise in the mother cell ATP level is not necessary for Pro-σK cleavage

Starvation of Bacillus subtilis initiates endosporulation involving formation of mother cell (MC) and forespore (FS) compartments. During engulfment, the MC membrane migrates around the FS and protein channels connect the two compartments. The channels are necessary for postengulfment FS gene expression, which relieves inhibition of SpoIVFB, an intramembrane protease that cleaves Pro-σ^K , releasing σ^K into the MC. SpoIVFB has an ATP-binding domain exposed to the MC cytoplasm, but the role of ATP in regulating Pro-σ^K cleavage has been unclear, as has the impact of the channels on MC and FS ATP levels. Using luciferase produced separately in each compartment to measure relative ATP concentrations during sporulation, we found that the MC ATP concentration rises about twofold coincident with increasing cleavage of Pro-σ^K , and the FS ATP concentration does not decline. Mutants lacking a channel protein or defective in channel protein turnover exhibited modest and varied effects on ATP levels, which suggested that low ATP concentration does not explain the lack of postengulfment FS gene expression in channel mutants. Furthermore, a rise in the MC ATP level was not necessary for Pro-σ^K cleavage by SpoIVFB, based on analysis of mutants that bypass the need for relief of SpoIVFB inhibition.

Levels of L-malate and other low molecular weight metabolites in spores of Bacillus species and Clostridium difficile

Dormant spores of Bacillus species lack ATP and NADH and contain notable levels of only a few other common low mol wt energy reserves, including 3-phosphoglyceric acid (3PGA), and glutamic acid. Recently, Bacillus subtilis spores were reported to contain ~ 30 μmol of L-malate/g dry wt, which also could serve as an energy reserve. In present work, L-malate levels were determined in the core of dormant spores of B. subtilis, Bacillus cereus, Bacillus megaterium and Clostridium difficile, using both an enzymatic assay and ¹³C-NMR on extracts prepared by several different methods. These assays found that levels of L-malate in B. cereus and B. megaterium spores were ≤ 0.5 μmol/g dry wt, and ≤ 1 μmol/g dry wt in B. subtilis spores, and levels of L-lactate and pyruvate in B. megaterium and B. subtilis spores were < 0.5 μmol/g dry wt. Levels of L-malate in C. difficile spores were ≤ 1 μmol/g dry wt, while levels of 3PGA were ~ 7 μmol/g; the latter value was determined by ³¹P-NMR, and is in between the 3PGA levels in B. megaterium and B. subtilis spores determined previously. ¹³C-NMR analysis of spore extracts further showed that B. megaterium, B. subtilis and C. difficile contained significant levels of carbonate/bicarbonate in the spore core. Low mol wt carbon-containing small molecules present at > 3 μmol/g dry spores are: i) dipicolinic acid, carbonate/bicarbonate and 3PGA in B. megaterium, B. subtilis and C. difficile; ii) glutamate in B. megaterium and B. subtilis; iii) arginine in B. subtilis; and iv) at least one unidentified compound in all three species.

Analysis of metabolism in dormant spores of Bacillus species by 31P nuclear magnetic resonance analysis of low-molecular-weight compounds

This work was undertaken to obtain information on levels of metabolism in dormant spores of Bacillus species incubated for weeks at physiological temperatures. Spores of Bacillus megaterium and Bacillus subtilis strains were harvested shortly after release from sporangia and incubated under various conditions, and dormant spore metabolism was monitored by (31)P nuclear magnetic resonance (NMR) analysis of molecules including 3-phosphoglyceric acid (3PGA) and ribonucleotides. Incubation for up to 30 days at 4, 37, or 50°C in water, at 37 or 50°C in buffer to raise the spore core pH from ∼6.3 to 7.8, or at 4°C in spent sporulation medium caused no significant changes in ribonucleotide or 3PGA levels. Stage I germinated spores of Bacillus megaterium that had slightly increased core water content and a core pH of 7.8 also did not degrade 3PGA and accumulated no ribonucleotides, including ATP, during incubation for 8 days at 37°C in buffered saline. In contrast, spores incubated for up to 30 days at 37 or 50°C in spent sporulation medium degraded significant amounts of 3PGA and accumulated ribonucleotides, indicative of RNA degradation, and these processes were increased in B. megaterium spores with a core pH of ∼7.8. However, no ATP was accumulated in these spores. These data indicate that spores of Bacillus species stored in water or buffer at low or high temperatures exhibited minimal, if any, metabolism of endogenous compounds, even when the spore core pH was 7.8 and core water content was increased somewhat. However, there was some metabolism in spores stored in spent sporulation medium.

Compartment-specific pH monitoring in Bacillus subtilis using fluorescent sensor proteins: a tool to analyze the antibacterial effect of weak organic acids

The internal pH (pH_i) of a living cell is one of its most important physiological parameters. To monitor the pH inside Bacillus subtilis during various stages of its life cycle, we constructed an improved version (IpHluorin) of the ratiometric, pH-sensitive fluorescent protein pHluorin by extending it at the 5′ end with the first 24 bp of comGA. The new version, which showed an approximate 40% increase in fluorescence intensity, was expressed from developmental phase-specific, native promoters of B. subtilis that are specifically active during vegetative growth on glucose (P_ptsG) or during sporulation (P_spoIIA, P_spoIIID, and P_sspE). Our results show strong, compartment-specific expression of IpHluorin that allowed accurate pH_i measurements of live cultures during exponential growth, early and late sporulation, spore germination, and during subsequent spore outgrowth. Dormant spores were characterized by an pH_i of 6.0 ± 0.3. Upon full germination the pH_i rose dependent on the medium to 7.0–7.4. The presence of sorbic acid in the germination medium inhibited a rise in the intracellular pH of germinating spores and inhibited germination. Such effects were absent when acetic was added at identical concentrations.

Genomic determinants of sporulation in Bacilli and Clostridia: towards the minimal set of sporulation-specific genes

Three classes of low-G+C Gram-positive bacteria (Firmicutes), Bacilli, Clostridia and Negativicutes, include numerous members that are capable of producing heat-resistant endospores. Spore-forming firmicutes include many environmentally important organisms, such as insect pathogens and cellulose-degrading industrial strains, as well as human pathogens responsible for such diseases as anthrax, botulism, gas gangrene and tetanus. In the best-studied model organism Bacillus subtilis, sporulation involves over 500 genes, many of which are conserved among other bacilli and clostridia. This work aimed to define the genomic requirements for sporulation through an analysis of the presence of sporulation genes in various firmicutes, including those with smaller genomes than B. subtilis. Cultivable spore-formers were found to have genomes larger than 2300 kb and encompass over 2150 protein-coding genes of which 60 are orthologues of genes that are apparently essential for sporulation in B. subtilis. Clostridial spore-formers lack, among others, spoIIB, sda, spoVID and safA genes and have non-orthologous displacements of spoIIQ and spoIVFA, suggesting substantial differences between bacilli and clostridia in the engulfment and spore coat formation steps. Many B. subtilis sporulation genes, particularly those encoding small acid-soluble spore proteins and spore coat proteins, were found only in the family Bacillaceae, or even in a subset of Bacillus spp. Phylogenetic profiles of sporulation genes, compiled in this work, confirm the presence of a common sporulation gene core, but also illuminate the diversity of the sporulation processes within various lineages. These profiles should help further experimental studies of uncharacterized widespread sporulation genes, which would ultimately allow delineation of the minimal set(s) of sporulation-specific genes in Bacilli and Clostridia.

Transcription of the Bacillus subtilis gerK operon, which encodes a spore germinant receptor, and comparison with that of operons encoding other germinant receptors

The gerA, gerB, and gerK operons, which encode germinant receptors in spores of Bacillus subtilis, were transcribed only in sporulation, and their mRNA levels peaked initially approximately 3 h before the initiation of accumulation of the spore's dipicolinic acid. After a rapid fall, levels of these mRNAs peaked again approximately 5 h later. In one wild-type strain (PS832), gerA mRNA was the most abundant, with levels of gerB and gerK mRNAs approximately 50% of that of gerA mRNA, whereas gerB mRNA was the most abundant in another wild-type strain (PY79). The synthesis of gerK mRNA in sporulation was abolished by loss of the forespore-specific RNA polymerase sigma factor, sigma(G), and induction of sigma(G) synthesis in vegetative cells led to synthesis of gerK mRNA. SpoVT, a regulator of sigma(G)-dependent gene expression, repressed gerK expression. The gerK promoter showed sequence similarities to sigma(G)-dependent promoters, and deletion of elements of this putative promoter abolished gerK expression in sporulation.

Levels of glycine betaine in growing cells and spores of Bacillus species and lack of effect of glycine betaine on dormant spore resistance

Bacteria of various Bacillus species are able to grow in media with very high osmotic strength in part due to the accumulation of low-molecular-weight osmolytes such as glycine betaine (GB). Cells of Bacillus species grown in rich and minimal media contained low levels of GB, but GB levels were 4- to 60-fold higher in cells grown in media with high salt. GB levels in Bacillus subtilis cells grown in minimal medium were increased approximately 7-fold by GB in the medium and 60-fold by GB plus high salt. GB was present in spores of Bacillus species prepared in media with or without high salt but at lower levels than in comparable growing cells. With spores prepared in media with high salt, GB levels were highest in B. subtilis spores and > or =20-fold lower in B. cereus and B. megaterium spores. Although GB levels in B. subtilis spores were elevated 15- to 30-fold by GB plus high salt in sporulation media, GB levels did not affect spore resistance. GB levels were similar in wild-type B. subtilis spores and spores that lacked major small, acid-soluble spore proteins but were much lower in spores that lacked dipicolinic acid.

Differential gene expression in genetically identical sister cells: the initiation of sporulation in Bacillus subtilis

Early in sporulation, the cell divides asymmetrically to give two sister compartments, a smaller prespore and a larger mother cell. Differential gene expression in these compartments depends on the regulation of the first sporulation-specific sigma factor, sigma(F), which is activated only in the prespore. Regulation relies on the interactions of four proteins -sigma(F), its antisigma SpoIIAB (which also has protein kinase activity), the anti-antisigma SpoIIAA and the protein phosphatase SpoIIE. Before asymmetric division, and in the mother cell after division, sigma(F) is held in an inactive complex with SpoIIAB and ATP; SpoIIAA is in its phosphorylated form. To disrupt the complex so as to liberate sigma(F) in the prespore, dephosphorylated SpoIIAA is needed, and this is made available by SpoIIE. Thereafter, SpoIIAB and SpoIIE are active simultaneously in the prespore, cycling SpoIIAA through phosphorylated and non-phosphorylated forms. This cycle detains SpoIIAB in a state in which it cannot inhibit sigma(F). Results from biophysical techniques, mathematical simulations and enzyme kinetics have now helped to elucidate the dynamics of the protein-protein interactions involved. An understanding of these dynamics largely accounts for the regulation of sigma(F). We show that the system is tuned to be highly efficient in its use of components and extremely economical in conserving ATP.

Efficient regulation of sigmaF, the first sporulation-specific sigma factor in B.subtilis

Differential gene expression is established in the prespore and mother-cell compartments of Bacillus subtilis through the successive activation of a series of cell-type-specific sigma factors. Crucial to the success of this process is the control of the first prespore-specific sigma factor, sigmaF. sigmaF is regulated by the proteins SpoIIAB, SpoIIAA and SpoIIE. SpoIIAB forms an inhibitory complex with sigmaF, which can be dissociated by interaction with SpoIIAA. During this interaction SpoIIAA is phosphorylated. SpoIIE is a membrane-bound phosphatase that dephosphorylates SpoIIAA, thereby re-activating it. It is not understood how sigmaF is activated specifically in the prespore but not in the mother cell. Here, we use a recently developed fluorescence spectroscopy technique to follow in real time the formation of sigmaF.SpoIIAB complexes and their dissociation by SpoIIAA. We show that complete activation of sigmaF is induced by a tenfold increase in SpoIIE activity. This result demonstrates that relatively small changes in SpoIIE activity, which could arise from asymmetric septation, can achieve the all-or-nothing response in sigmaF activity required by the cell. For long-term sigmaF activation, we find that sustained SpoIIE activity is required to counteract the activity of SpoIIAB. Even though the continual phosphorylation and dephosphorylation of SpoIIAA by these two enzymes will expend some ATP, the formation of SpoIIAA.SpoIIAB.ADP complexes greatly diminishes the rate of the phosphorylation reaction, and thus minimizes the wastage of energy. These features provide a very efficient system for regulating sigmaF.

Compartmentalization of gene expression during Bacillus subtilis spore formation

Gene expression in members of the family Bacillaceae becomes compartmentalized after the distinctive, asymmetrically located sporulation division. It involves complete compartmentalization of the activities of sporulation-specific sigma factors, sigma(F) in the prespore and then sigma(E) in the mother cell, and then later, following engulfment, sigma(G) in the prespore and then sigma(K) in the mother cell. The coupling of the activation of sigma(F) to septation and sigma(G) to engulfment is clear; the mechanisms are not. The sigma factors provide the bare framework of compartment-specific gene expression. Within each sigma regulon are several temporal classes of genes, and for key regulators, timing is critical. There are also complex intercompartmental regulatory signals. The determinants for sigma(F) regulation are assembled before septation, but activation follows septation. Reversal of the anti-sigma(F) activity of SpoIIAB is critical. Only the origin-proximal 30% of a chromosome is present in the prespore when first formed; it takes approximately 15 min for the rest to be transferred. This transient genetic asymmetry is important for prespore-specific sigma(F) activation. Activation of sigma(E) requires sigma(F) activity and occurs by cleavage of a prosequence. It must occur rapidly to prevent the formation of a second septum. sigma(G) is formed only in the prespore. SpoIIAB can block sigma(G) activity, but SpoIIAB control does not explain why sigma(G) is activated only after engulfment. There is mother cell-specific excision of an insertion element in sigK and sigma(E)-directed transcription of sigK, which encodes pro-sigma(K). Activation requires removal of the prosequence following a sigma(G)-directed signal from the prespore.

Properties of spores of Bacillus subtilis blocked at an intermediate stage in spore germination

Germination of mutant spores of Bacillus subtilis unable to degrade their cortex is accompanied by excretion of dipicolinic acid and uptake of some core water. However, compared to wild-type germinated spores in which the cortex has been degraded, the germinated mutant spores accumulated less core water, exhibited greatly reduced enzyme activity in the spore core, synthesized neither ATP nor reduced pyridine or flavin nucleotides, and had significantly higher resistance to heat and UV irradiation. We propose that the germinated spores in which the cortex has not been degraded represent an intermediate stage in spore germination, which we term stage I.

Effects of major spore-specific DNA binding proteins on Bacillus subtilis sporulation and spore properties

Sporulation of a Bacillus subtilis strain (termed alpha(-) beta(-)) lacking the majority of the alpha/beta-type small, acid-soluble spore proteins (SASP) that are synthesized in the developing forespore and saturate spore DNA exhibited a number of differences from that of the wild-type strain, including delayed forespore accumulation of dipicolinic acid, overexpression of forespore-specific genes, and delayed expression of at least one mother cell-specific gene turned on late in sporulation, although genes turned on earlier in the mother cell were expressed normally in alpha(-) beta(-) strains. The sporulation defects in alpha(-) beta(-) strains were corrected by synthesis of chromosome-saturating levels of either of two wild-type, alpha/beta-type SASP but not by a mutant SASP that binds DNA poorly. Spores from alpha(-) beta(-) strains also exhibited less glutaraldehyde resistance and slower outgrowth than did wild-type spores, but at least some of these defects in alpha(-) beta(-) spores were abolished by the synthesis of normal levels of alpha/beta-type SASP. These results indicate that alpha/beta-type SASP may well have global effects on gene expression during sporulation and spore outgrowth.

The katX gene, which codes for the catalase in spores of Bacillus subtilis, is a forespore-specific gene controlled by sigmaF, and KatX is essential for hydrogen peroxide resistance of the germinating spore

Previous work has shown that the katX gene encodes the major catalase in dormant spores of Bacillus subtilis but that this enzyme has no role in dormant spore resistance to hydrogen peroxide. Expression of a katX-lacZ fusion began at approximately h 2 of sporulation, and >75% of the katX-driven beta-galactosidase was packaged into the mature spore. A mutation in the gene coding for the sporulation-specific RNA polymerase sigma factor sigmaF abolished katX-lacZ expression, while mutations in genes encoding sigmaE, sigmaG, and sigmaK did not. Induction of sigmaF synthesis in vegetative cells also resulted in katX-lacZ expression, while induction of sigmaG expression did not; the katX-lacZ fusion was also not induced by hydrogen peroxide. Upstream of the in vivo katX transcription start site there are sequences with good homology to those upstream of known sigmaF-dependent start sites. These data indicate that katX is an additional member of the forespore-specific sigmaF regulon. A mutant in the katA gene, encoding the major catalase in growing cells, was sensitive to hydrogen peroxide during sporulation, while a katX mutant was not. However, outgrowth of katX spores, but not katA spores, was sensitive to hydrogen peroxide. Consequently, a major function for KatX is to protect germinating spores from hydrogen peroxide.

Analysis of the relationship between the decrease in pH and accumulation of 3-phosphoglyceric acid in developing forespores of Bacillus species

Analysis of the pH decrease and 3-phosphoglyceric acid (3PGA) accumulation in the forespore compartment of sporulating cells of Bacillus subtilis showed that the pH decrease of 1 to 1.2 units at approximately 4 h of sporulation preceded 3PGA accumulation, as observed previously in B. megaterium. These data, as well as analysis of the forespore pH decrease in asporogenous mutants of B. subtilis, indicated that sigma G-dependent forespore transcription, but not sigma K-dependent mother cell transcription, is required for the forespore pH decrease. Further analysis of these asporogenous mutants showed an excellent correlation between the forespore pH decrease and the forespore's accumulation of 3PGA. These latter results are consistent with our previous suggestion that the decrease in forespore pH results in greatly decreased activity of phosphoglycerate mutase in the forespore, which in turn leads to 3PGA accumulation. In further support of this suggestion, we found that (i) elevating the pH of developing forespores of B. megaterium resulted in rapid utilization of the forespore's 3PGA depot and (ii) increasing forespore levels of PGM approximately 10-fold in B. subtilis resulted in a large decrease in the spore's depot of 3PGA. The B. subtilis strain with a high phosphoglycerate mutase level sporulated, and the spores germinated and went through outgrowth normally, indicating that forespore accumulation of a large 3PGA depot is not essential for these processes.

Autoprocessing of the protease that degrades small, acid-soluble proteins of spores of Bacillus species is triggered by low pH, dehydration, and dipicolinic acid

The sequence-specific protease (termed GPR) that degrades small, acid-soluble proteins (SASP) during germination of spores of Bacillus species is synthesized during sporulation as an inactive precursor termed P46. Approximately 2 h later in sporulation, P46 is converted proteolytically to a smaller form, termed P41, which is active in vitro, but which does not act significantly on SASP in vivo until spore germination is initiated. While it appears likely that P46-->P41 conversion is an autoprocessing event, the mechanisms regulating P46-->P41 conversion in vivo are not clear. In this work we found that P46-->P41 conversion in vitro was stimulated tremendously in an allosteric manner by pyridine-2,6-dicarboxylic acid (dipicolinic acid [DPA]) plus Ca2+ but not by Ca2+ in combination with a variety of DPA analogs. The processing reaction stimulated by Ca(2+)-DPA was seen at pH 5.1 but not at pH 6.2 or 7, and under these conditions P46-->P41 conversion exhibited a linear time course and was a first-order reaction, indicative of an intramolecular autoprocessing reaction. At pH 5.1, P46-->P41 conversion was stimulated markedly by very high ionic strength. At pHs from 5.1 to 6.6, P46-->P41 conversion also occurred when P46 was dehydrated to approximately 54% relative humidity. This processing was stimulated markedly when dehydration was carried out in the presence of DPA and NaCl but was greatly decreased when dehydration was to 10, 33, or 75% relative humidity. Since previous work has shown that P(46)-->P(41) processing in vivo takes place (i) after a fall in forespore pH to 6.3 to 6.9 and approximately in parallel with (ii) DPA accumulation by the forespore and (iii) dehydration of the forespore, out new finings in vitro suggest that these three changes may synergistically trigger P(46)-->P(41) autoprocessing in the developing forespore. Presumably the conditions in vivo during this authoprocessing preclude significant attack of the P(41) generated on its SASP substrates.

Mineralization and responses of bacterial spores to heat and oxidative agents

Mineralization of bacterial spores with Ca2+ and a variety of other mineral cations enhances resistance to heat damage. Part of the enhancement is associated with increased dehydration of the mineralized protoplast or spore core, while part is independent of dehydration and effective for resistance even to dry heat. Spore mineralization was found also to enhance resistance to oxidative damage caused by agents such as tertiary butyl hydroperoxide or H2O2. In contrast, mineral cations in the environment increased oxidative damage, presumably by catalyzing radical formation. Metal ion chelators such as o-phenanthroline protected spores against such damage.

Cloning and nucleotide sequences of the genes encoding triose phosphate isomerase, phosphoglycerate mutase, and enolase from Bacillus subtilis

The Bacillus subtilis genes tpi, pgm, and eno, encoding triose phosphate isomerase, phosphoglycerate mutase (PGM), and enolase, respectively, have been cloned and sequenced. These genes are the last three in a large putative operon coding for glycolytic enzymes; the operon includes pgk (coding for phosphoglycerate kinase) followed by tpi, pgm, and eno. The triose phosphate isomerase and enolase from B. subtilis are extremely similar to those from all other species, both eukaryotic and prokaryotic. However, B. subtilis PGM bears no resemblance to mammalian, fungal, or gram-negative bacterial PGMs, which are dependent on 2,3-diphosphoglycerate (DPG) for activity. Instead, B. subtilis PGM, which is DPG independent, is very similar to a DPG-independent PGM from a plant species but differs from the latter in the absolute requirement of B. subtilis PGM for Mn2+. The cloned pgm gene has been used to direct up to 25-fold overexpression of PGM in Escherichia coli; this should facilitate purification of large amounts of this novel Mn(2+)-dependent enzyme. Inactivation of pgm plus eno in B. subtilis resulted in extremely slow growth either on plates or in liquid, but growth of these mutants was enhanced by supplementation of media with malate. However, these mutants were asporogenous with or without malate supplementation.

Analysis by fluorescence microscopy of the development of compartment-specific gene expression during sporulation of Bacillus subtilis

The use of a fluorogenic substrate, 5-octanoylaminofluorescein-di-beta-D-galactopyranoside, for beta-galactosidase has made it possible to visualize enzyme activity in individual cells of sporulating populations of Bacillus subtilis by fluorescence microscopy. lacZ fusions to different sporulation-associated genes have been used to investigate the cell compartmentalization of gene expression during sporulation. A strain with a lacZ fusion to sspA, a gene which is transcribed by E-sigma G at a late stage of sporulation, displayed predominantly compartment-specific fluorescence. Expression of the early-expressed spoIIA locus, which includes the structural gene for sigma F, was seen not to be compartmentalized. Populations of strains with lacZ fusions to gpr and dacF, genes which are transcribed by E-sigma F at intermediate stages of sporulation, included some organisms showing uncompartmentalized fluorescence and others showing compartment-specific fluorescence; the proportion showing compartment-specific fluorescence increased in samples taken later in sporulation. Several possible explanations of the results obtained with gpr and dacF are considered. A plausible interpretation is that sigma F activity is initially not compartmentalized and becomes compartmentalized as sporulation progresses. The progression to compartmentalization does not require the activities of the sporulation-specific factor sigma E or sigma G but may require some product of sigma F activity.

An adenosine nucleotide switch controlling the activity of a cell type-specific transcription factor in B. subtilis

The sigma F factor establishes cell type-specific gene transcription during sporulation in B. subtilis. sigma F is negatively regulated by SpollAB, which forms complexes with sigma F or SpollAA. ATP and its nonhydrolyzable analogs stimulate the formation of the SpollAB.sigma F complex, whereas ADP stimulates the formation of the SpollAB.SpollAA complex. Which protein SpollAB associates with is determined by the concentrations of the two nucleotides, on which basis we propose a partner-switching model for the regulation of sigma F: [formula: see text] Consistent with this model, SpollAA reverses SpollAB-mediated inhibition of sigma F-directed transcription in a manner that depends on ADP. Cell-specific activation of sigma F could be due to an alteration in adenosine nucleotide levels in one cell of the sporangium.

The internal pH of the forespore compartment of Bacillus megaterium decreases by about 1 pH unit during sporulation

Previous work has shown that the internal pH of dormant spores of Bacillus species is more than 1 pH U below that of growing cells but rises to that of growing cells in the first minutes of spore germination. In the present work the internal pH of the whole Bacillus megaterium sporangium was measured by the distribution of the weak base methylamine and was found to decrease by approximately 0.4 during sporulation. By using fluorescence ratio image analysis with a fluorescein derivative, 2',7'-bis(2-carboxyethyl)-5 (and -6)-carboxyfluorescein (BCECF), whose fluorescence is pH sensitive, the internal pH of the mother cell was found to remain constant during sporulation at a value of 8.1, similar to that in the vegetative cell. Whereas the internal pH of the forespore was initially approximately 8.1, this value fell to approximately 7.0 approximately 90 min before synthesis of dipicolinic acid and well before accumulation of the depot of 3-phosphoglyceric acid. The pH in the forespore compartment was brought to that of the mother cell by suspending sporulating cells in a pH 8 potassium phosphate buffer plus the ionophore nigericin to clamp the internal pH of the cells to that of the external medium. We suggest that at a minimum, acidification of the forespore may regulate the activity of phosphoglycerate mutase, which is the enzyme known to be regulated to allow 3-phosphoglyceric acid accumulation during sporulation.

Binding of small, acid-soluble spore proteins to DNA plays a significant role in the resistance of Bacillus subtilis spores to hydrogen peroxide

Dormant spores of Bacillus subtilis which lack the majority of the alpha/beta-type small, acid-soluble proteins (SASP) (termed alpha- beta- spores) that coat the DNA in wild-type spores are significantly more sensitive to hydrogen peroxide than are wild-type spores. Hydrogen peroxide treatment of alpha- beta- spores causes DNA strand breaks more readily than does comparable treatment of wild-type spores, and alpha- beta- spores, but not wild-type spores, which survive hydrogen peroxide treatment have acquired a significant number of mutations. The hydrogen peroxide resistance of wild-type spores appears to be acquired in at least two incremental steps during sporulation. The first increment is acquired at about the time of alpha/beta-type SASP synthesis, and the second increment is acquired approximately 2 h later, at about the time of dipicolinic acid accumulation. During sporulation of the alpha- beta- strain, only the second increment of hydrogen peroxide resistance is acquired. In contrast, sporulation mutants which accumulate alpha/beta-type SASP but progress no further in sporulation acquire only the first increment of hydrogen peroxide resistance. These findings strongly suggest that binding of alpha/beta-type SASP to DNA provides one increment of spore hydrogen peroxide resistance. Indeed, binding of alpha/beta-type SASP to DNA in vitro provides strong protection against cleavage of DNA by hydrogen peroxide.

Evidence that the spoIIM gene of Bacillus subtilis is transcribed by RNA polymerase associated with sigma E

We have investigated the temporal and spatial regulation of spoIIM, a gene of Bacillus subtilis whose product is required for complete septum migration and engulfment of the forespore compartment during sporulation. The spoIIM promoter was found to become active about 2 h after the initiation of sporulation. The effects of mutations on the expression of a spoIIM-lacZ fusion were most consistent with its utilization by sigma-E-associated RNA polymerase (E sigma E). A unique 5' end of the in vivo spoIIM transcript was detected by primer extension analysis and was determined to initiate at the appropriate distance from a sequence conforming very closely to the consensus for genes transcribed by E sigma E. A partially purified preparation of E sigma E produced a transcript in vitro that initiated at the same nucleotide as the primer extension product generated from in vivo RNA. Ectopic induction of sigma E synthesis during growth resulted in the immediate and strong expression of a spoIIM-lacZ fusion, but an identical fusion was completely unresponsive to induced synthesis of either sigma F or sigma G under similar conditions. The results of plasmid integration-excision experiments in which the spoIIM gene was reversibly disrupted by a temperature-sensitive integrational vector suggested that spoIIM expression is required in the forespore compartment, but direct examination of subcellular fractions enriched for mother cell or forespore material indicated that spoIIM expression cannot be confined to the forespore. We conclude that spoIIM is a member of the sigma E regulon and that it may be transcribed exclusively by E sigma E. We discuss the implications of this conclusion for models in which activation of sigma E in the mother cell is proposed to be a part of the mechanism responsible for initiating separate programs of gene activity in the two sporangium compartments.

Bacillus subtilis sporulation: regulation of gene expression and control of morphogenesis

Bacillus subtilis sporulation is an adaptive response to nutritional stress and involves the differential development of two cells. In the last 10 years or so, virtually all of the regulatory genes controlling sporulation, and many genes directing the structural and morphological changes that accompany sporulation, have been cloned and characterized. This review describes our current knowledge of the program of gene expression during sporulation and summarizes what is known about the functions of the genes that determine the specialized biochemical and morphological properties of sporulating cells. Most steps in the genetic program are controlled by transcription factors that have been characterized in vitro. Two sporulation-specific sigma factors, sigma E and sigma F, appear to segregate at septation, effectively determining the differential development of the mother cell and prespore. Later, each sigma is replaced by a second cell-specific sigma factor, sigma K in the mother cell and sigma G in the prespore. The synthesis of each sigma factor is tightly regulated at both the transcriptional and posttranslational levels. Usually this regulation involves an intercellular interaction that coordinates the developmental programmes of the two cells. At least two other transcription factors fine tune the timing and levels of expression of genes in the sigma E and sigma K regulons. The controlled synthesis of the sigma factors and other transcription factors leads to a spatially and temporally ordered program of gene expression. The gene products made during each successive stage of sporulation help to bring about a sequence of gross morphological changes and biochemical adaptations. The formation of the asymmetric spore septum, engulfment of the prespore by the mother cell, and formation of the spore core, cortex, and coat are described. The importance of these structures in the development of the resistance, dormancy, and germination properties of the spore is assessed.

Properties of purified sporlets produced by spoII mutants of Bacillus subtilis

A number of abortively disporic spoII mutants of Bacillus subtilis released their forespore compartments (termed stage II sporlets) after mother cell lysis during sporulation in nutrient exhaustion or resuspension media. Stage II sporlets were viable and contained levels of ATP and a number of enzymes similar to those in cells 2 to 3 h after sporulation. However, stage II sporlets carried out essentially no macromolecular synthesis, a result suggesting that they were in a quiescent state. The nucleoid of these quiescent stage II sporlets was significantly condensed relative to that in the original vegetative cells, as was previously found to take place 1 to 2 h after initiation of sporulation (B. Setlow, N. Magill, P. Febbroriello, L. Nakhimousky, D. E. Koppel, and P. Setlow, J. Bacteriol. 173:6270-6278, 1991). Stage II sporlets may be a useful model system for analysis of forespore properties early in stage II of sporulation.

Dramatic increase in negative superhelicity of plasmid DNA in the forespore compartment of sporulating cells of Bacillus subtilis

Plasmid pUB110, isolated from vegetative cells of Bacillus subtilis, has an average of 34 negative supertwists (tau av = -34). This value falls to -30 early in sporulation, and the plasmid in the mother cell compartment maintains a tau av of -30. However, the plasmid within the developing forespore becomes much more negatively supercoiled, reaching a tau av of -47 in the dormant spore. This increased negative supercoiling in the forespore plasmid takes place in parallel with the synthesis of small, acid-soluble spore proteins, alpha and beta; and the plasmid from spores lacking small, acid-soluble proteins alpha and beta has a tau av of -40. The large increase in negative supercoiling of spore plasmid was also observed with Bacillus megaterium and in B. subtilis containing a plasmid with an origin different from that of pUB110. During spore germination plasmid pUB110 rapidly relaxed back to the tau av value characteristic of vegetative cells. It is possible that the observed changes in forespore plasmid topology are involved in modulating gene expression, DNA photochemistry, or both of these parameters in this compartment.

Evidence for an additional temporal class of gene expression in the forespore compartment of sporulating Bacillus subtilis

We present evidence indicating that the previously studied, sporulation-induced gene 0.3 kb, which encodes a stable RNA present at late developmental stages, is transcribed in the forespore chamber of sporulating cells of Bacillus subtilis. Compartmentalized gene expression was demonstrated on the basis of subcellular fractionation experiments in which severalfold-higher levels of 0.3 kb-directed beta-galactosidase specific activity were observed in forespore extracts than in extracts from the mother cell and dependence studies in which 0.3 kb transcription was found to be blocked in mutants bearing mutations in spoIIIA, spoIIIE, and spoIIIG, genes which are known to govern forespore gene expression. Also, 0.3 kb transcription could be switched on during growth in cells in which transcription of the forespore regulatory gene spoIIIG was engineered to be activated in response to the lac inducer IPTG (isopropyl-beta-D-thiogalactopyranoside). Although it is transcribed in the forespore, 0.3 kb is switched on at a later developmental stage than other previously studied forespore-expressed genes, and hence it appears to be representative of an additional temporal class of compartmentalized gene expression.

Compartment-specific transcription in Bacillus subtilis: identification of the promoter for gdh

Glucose dehydrogenase beings to accumulate in the forespore between 2 and 3 h after the onset of endospore formation in Bacillus subtilis. The promoter for the structural gene for glucose dehydrogenase (gdh) was shown to be located 800 base pairs upstream from the coding sequence by examining the effects of integrating plasmids into the gdh region of the chromosome. The location of the gdh promoter was confirmed by primer extension analysis and by the identification of two single-base substitutions in the gdh promoter that prevented its function. The results of cell fractionation experiments with a strain that contained a transcriptional fusion of the gdh promoter and lacZ indicated that the forespore-specific accumulation of glucose dehydrogenase during sporulation is probably due to forespore-specific transcription of gdh.

The promoter for a sporulation gene in the spoIVC locus of Bacillus subtilis and its use in studies of temporal and spatial control of gene expression

We have identified the transcription start site and regulatory region governing the expression of a sporulation gene in the spoIVC locus of Bacillus subtilis. Efficient expression and developmental regulation of this gene was controlled from a promoter region that extended no more than 110 base pairs upstream and no more than 4 base pairs downstream from the start site of transcription, on which basis we infer that spoIVC is regulated at the level of transcription initiation. Using a transcriptional fusion of the spoIVC gene to the lacZ gene of Escherichia coli, we found that spoIVC expression was turned on at the third to fourth hour of sporulation (at about the developmental stage [IV] that its products are required in spore formation) and that this transcription was largely restricted to the mother cell chamber of the sporangium. Mutations in many different spo genes (causing blocks at stages 0 to V) were found to influence (negatively and positively) the level of spoIVC expression. Our results distinguish the mode of spoIVC regulation from that of previously studied sporulation genes and indicate that it is representative of a new regulon of mother cell-specific gene expression.

Levels of mRNAs which code for small, acid-soluble spore proteins and their LacZ gene fusions in sporulating cells of Bacillus subtilis

The levels of mRNAs from genes (sspA, B and E) which code for major small, acid-soluble, spore proteins of Bacillus subtilis have been determined, as well as the levels of mRNAs from ssp-lacZ gene fusions. Increasing the gene dosage of ssp-lacZ fusions resulted in parallel increases in both the ssp-lacZ mRNA level and the rate of b-galactosidase accumulation. Similarly, an 11-fold increase in sspE gene dosage gave a comparable increase in sspE mRNA, but at most a 1.5-fold increase in the amount of sspE gene product accumulated. In contrast, an 11-fold increase in the dosage of the sspA or B genes had no significant effect on the level of total sspA plus sspB mRNA, but did alter the ratios of these mRNAs as well as the amount of their gene products, to reflect the altered ratio of the two genes. These results suggest that intact ssp genes, but not ssp-lacZ gene fusions, are subject to feedback regulation of gene expression, with this regulation of the sspA and B genes effected by modulation of mRNA levels, while the feedback regulation of the sspE gene is at the post-transcriptional level.

Respiratory systems of the Bacillus cereus mother cell and forespore

The respiratory systems of the mother cells and forespores of Bacillus cereus were compared throughout the maturation stages (III to VI) of sporulation. The results indicated that both cell compartments contain the same assortment of oxidoreductases and cytochromes. However membrane fractions from young forespores were clearly distinct from those of the mother cell, i.e., lower content of cytochrome aa3, lower cytochrome c oxidase activity, higher concentration of cytochrome o, and a lower sensitivity of the respiration to the inhibiting effect of cyanide. This suggests that the cyanide-resistant pathway contributes more importantly to forespore respiratory activity than to activity in the mother cell compartment. During the maturation stages, the forespore NADH oxidase activity declined faster than in the mother cells. Other activities studied decreased steadily in both cell compartments. These findings together with the analysis of the kinetics of NADH-dependent reduction of cytochromes in the mature spore membranes indicated an impairment of electron flow between NADH dehydrogenase and cytochrome b. This impairment could be overcome by the addition of menadione.

Red pigment in Bacillus megaterium spores

Bacillus megaterium QM B1551 spores contained a unique red pigment in their membranes that was not found in other species. This red pigment, presumably a carotenoid, was synthesized about the time of dipicolinic acid synthesis during sporulation and was associated with the forespores. A yellow pigment was synthesized during sporulation in rich medium and was found in the mother cell compartment. Although the yellow pigment was also associated with spores, it could be removed by two different extraction procedures without impairing germination; it was absent when sporulation occurred in a minimal medium. Although the yellow pigment of the mother cell appeared to be dispensable, the red pigment may serve a more critical function, such as membrane stabilization.

Enzymatic activity of precursors of Bacillus megaterium spore protease

The protease that initiates rapid proteolysis during germination of Bacillus megaterium spores is synthesized during sporulation as a 46,000-molecular-weight polypeptide (P46) and is processed later in sporulation to a 41,000-molecular-weight polypeptide (P41), which is converted to a 40,000-molecular-weight polypeptide (P40) early in spore germination. P40 is known to be both tetrameric and enzymatically active. In this work, we show that P46 and P41 are both tetrameric, but that only P41 is enzymatically active. The identification of a zymogen form (P46) of this protease explains in part the regulation of the activity of this enzyme.

Purification and characterization of a Bacillus megaterium disulfide reductase specific for disulfides containing pantethine 4',4"-diphosphate

An NADH-linked disulfide reductase specific for disulfides containing pantethine 4',4"-diphosphate moieties was purified 23,000-fold to homogeneity from spores of Bacillus megaterium. The enzyme had a native molecular weight of 122,000 with two apparently identical subunits, contained one molecule of flavin adenine dinucleotide per subunit, and was inhibited by the vicinal dithiol reagent arsenite. The enzyme was active only on disulfides containing pantethine 4',4"-diphosphate moieties, including pantethine 4',4"-diphosphate, oxidized coenzyme A, and coenzyme A in disulfide linkage to acyl carrier protein. However, the Km values for pantethine 4',4"-diphosphate and oxidized coenzyme A were 0.65 and 7.4 mM, respectively. The enzyme was at a low level in log-phase cells but increased up to 10-fold early in the stationary phase and had a similar specific activity in both the mother cell and the forespore compartment; the enzyme activity fell only slowly during spore germination and outgrowth. The enzyme was not detected in several eucaryotic sources and was present in at most a low level in a number of gram-negative bacteria. Surprisingly, the specific activity of this enzyme varied more than 200-fold in extracts from different Bacillus species, with values in B. subtilis being 5- to 6-fold lower and values in B. cereus and B. sphaericus being 8- and 35-fold higher, respectively, than the maximum value in B. megaterium. However, the high specific activity in B. sphaericus did not represent more enzyme protein than in B. megaterium. The possible function of this newly discovered enzyme is discussed.

Bacillus megaterium spore protease: purification, radioimmunoassay, and analysis of antigen level and localization during growth, sporulation, and spore germination

The protease which initiates the massive protein degradation early in bacterial spore germination has been purified from Bacillus megaterium spores. The enzyme has a molecular weight of 160,000 and contains four apparently identical subunits, but only the tetramer is enzymatically active. A radioimmunoassay has been developed for this enzyme and has been used to show that the protease is absent from growing cells, but appears early in sporulation within the developing forespore. In contrast, the protease antigen disappears rapidly during spore germination, in parallel with the loss in enzyme activity.

Noninvolvement of the spore cortex in acquisition of low-molecular-weight basic proteins and UV light resistance during Bacillus sphaericus sporulation

Two major low-molecular weight, acid-soluble proteins (termed A and B proteins) were purified from Bacillus sphaericus spores and had properties similar to those of the analogous proteins from spores of other Bacillus species. These proteins were accumulated late in sporulation, when the developing spores became resistant to UV light, and were degraded during spore germination by a spore protease. A mutant of B. sphaericus unable to make spore cortex because of a block in diaminopimelic acid (DAP) biosynthesis accumulated and maintained levels of the A and B proteins similar to those in the DAP+ parent or the DAP- strain in which cortex formation was restored by growth with DAP. In addition, the DAP- strain grown without DAP acquired a level of UV light resistance identical to that of wild-type spores and at the time of appearance of the A and B proteins. These findings indicate that formation of little, if any, spore cortex is required for acquisition of UV light resistance or maintenance of high levels of A and B proteins. The data provide further support for a role of the A and B proteins in the spore's UV light resistance.

Levels of H+ and other monovalent cations in dormant and germinating spores of Bacillus megaterium

Previous investigators using the extent of uptake of the weak base methylamine to measure internal pH have shown that the pH in the core region of dormant spores of Bacillus megaterium is 6.3 to 6.5. Elevation of the internal pH of spores by 1.6 U had no significant effect on their degree of dormancy or their heat or ultraviolet light resistance. Surprisingly, the rate of methylamine uptake into dormant spores was slow (time for half-maximal uptake, 2.5 h at 24 degrees C). Most of the methylamine taken up by dormant spores was rapidly (time for half-maximal uptake, less than 3 min) released during spore germination as the internal pH of spores rose to approximately 7.5. This rise in internal spore pH took place before dipicolinic acid release, was not abolished by inhibition of energy metabolism, and during germination at pH 8.0 was accompanied by a decrease in the pH of the germination medium. Also accompanying the rise in internal spore pH during germination was the release of greater than 80% of the spores K+ and Na+. The K+ was subsequently reabsorbed in an energy-dependent process. These data indicate (i) that between pH 6.2 and 7.8 internal spore pH has little effect on dormant spore properties, (ii) that there is a strong permeability barrier in dormant spores to movement of charged molecules and small uncharged molecules, and (iii) that extremely early in spore germination this permeability barrier is breached, allowing rapid release of internal monovalent cations (H+, Na+, and K+).

Bacillus megaterium sporal peptidoglycan synthesis studied by high-resolution autoradiography

Cells of a Dap- Lys- mutant strain of Bacillus megaterium were pulse labeled with [3H]diaminopimelic acid at different times of growth and sporulation. They were processed for radioactivity measurements and high-resolution autoradiography either just after the pulse or after a chase in a nonradioactive medium until refractile forespores started to appear at time (t)4,5. In the pulse-labeled cells, autoradiographs and radioactivity measurements showed that the radioactivity incorporated during a pulse decreased abruptly after t0 and stayed at a low level until t5, although the forespore wall and cortex were formed between t4 and t5. In the pulse-chased bacteria, the acid-insoluble radioactivity, as well as the number of silver grains on autoradiographs, increased during the chase in cells labeled at t1 to t2, whereas it decreased in those labeled before t0. Furthermore, analysis of silver grain distribution showed that, in stage IV bacteria, grains were distributed at the outside of the forespore, mostly on the sporangium cell wall, when pulse-labeling occurred before or at t0; they were located along the cortex and in the forespore cytoplasm when labeling was made at t1 or t2. These facts show that [3H]diaminopimelic acid necessary for spore envelope synthesis was incorporated before their morphological appearance. Free or small diaminopimelic acid precursors entered the sporangium between t1 and t2. The appearance of silver grains in the forespore cytoplasm suggests that the forespore is implicated in sporal peptidoglycan synthesis.