Enzymatic activity of precursors of Bacillus megaterium spore protease

Small acid-soluble spore proteins of Clostridium acetobutylicum are able to protect DNA in vitro and are specifically cleaved by germination protease GPR and spore protease YyaC

Small acid-soluble proteins (SASPs) play an important role in protection of DNA in dormant bacterial endospores against damage by heat, UV radiation or enzymic degradation. In the genome of the strict anaerobe Clostridium acetobutylicum, five genes encoding SASPs have been annotated and here a further sixth candidate is suggested. The ssp genes are expressed in parallel dependent upon Spo0A, a master regulator of sporulation. Analysis of the transcription start points revealed a σG or a σF consensus promoter upstream of each ssp gene, confirming a forespore-specific gene expression. SASPs were termed SspA (Cac2365), SspB (Cac1522), SspD (Cac1620), SspF (Cac2372), SspH (Cac1663) and Tlp (Cac1487). Here it is shown that with the exception of Tlp, every purified recombinant SASP is able to bind DNA in vitro thereby protecting it against enzymic degradation by DNase I. Moreover, SspB and SspD were specifically cleaved by the two germination-specific proteases GPR (Cac1275) and YyaC (Cac2857), which were overexpressed in Escherichia coli and activated by an autocleavage reaction. Thus, for the first time to our knowledge, GPR-like activity and SASP specificity could be demonstrated for a YyaC-like protein. Collectively, the results assign SspA, SspB, SspD, SspF and SspH of C. acetobutylicum as members of α/β-type SASPs, whereas Tlp seems to be a non-DNA-binding spore protein of unknown function. In acetic acid-extracted proteins of dormant spores of C. acetobutylicum, SspA was identified almost exclusively, indicating its dominant biological role as a major α/β-type SASP in vivo.

Proteolytic processing of the protease which initiates degradation of small, acid-soluble proteins during germination of Bacillus subtilis spores

Degradation of small, acid-soluble spore proteins during germination of Bacillus subtilis spores is initiated by a sequence-specific protease called GPR. Western blot (immunoblot) analysis of either Bacillus megaterium or B. subtilis GPR expressed in B. subtilis showed that GPR is synthesized at about the third hour of sporulation in a precursor form and is processed to an approximately 2- to 5-kDa-smaller species 2 to 3 h later, at or slightly before the time of accumulation of dipicolinic acid by the forespore. This was found with both normal levels of expression of B. subtilis and B. megaterium GPR in B. subtilis, as well as when either protein was overexpressed up to 100-fold. The sporulation-specific processing of GPR was blocked in all spoIII, -IV, and -V mutants tested (none of which accumulated dipicolinic acid), but not in a spoVI mutant which accumulated dipicolinic acid. The amino-terminal sequences of the B. megaterium and B. subtilis GPR initially synthesized in sporulation were identical to those predicted from the coding genes' sequences. However, the processed form generated in sporulation lacked 15 (B. megaterium) or 16 (B. subtilis) amino-terminal residues. The amino acid sequence surrounding this proteolytic cleavage site was very homologous to the consensus sequence recognized and cleaved by GPR in its small, acid-soluble spore protein substrates. This observation, plus the efficient processing of overproduced GPR during sporulation, suggests that the GPR precursor may autoproteolyze itself during sporulation. During spore germination, the GPR from either species expressed in B. subtilis was further processed by removal of one additional amino-terminal amino acid (leucine), generating the mature protease which acts during spore germination.

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.

Cloning, nucleotide sequence, and regulation of the Bacillus subtilis gpr gene, which codes for the protease that initiates degradation of small, acid-soluble proteins during spore germination

The gpr gene, which codes for the protease that initiates degradation of small, acid-soluble proteins during spore germination, has been cloned from Bacillus megaterium and Bacillus subtilis, and its nucleotide sequence has been determined. Use of a translational gpr-lacZ fusion showed that the B. subtilis gpr gene was expressed primarily, if not exclusively, in the forespore compartment of the sporulating cell, with expression taking place approximately 1 h before expression of glucose dehydrogenase and ssp genes. gpr-lacZ expression was abolished in spoIIAC (sigF) and spoIIIE mutants but was reduced only approximately 50% in a spoIIIG (sigG) mutant. However, the kinetics of the initial approximately 50% of gpr-lacZ expression were unaltered in a spoIIIG mutant. The in vivo transcription start site of gpr has been identified and found to be identical to the in vitro start site on this gene with either E sigma F or E sigma G. Induction of sigma G synthesis in vivo turned on gpr-lacZ expression in parallel with synthesis of glucose dehydrogenase. These data are consistent with gpr transcription during sporulation first by E sigma F and then by E sigma G.

Control of intracellular serine protease expression in Bacillus subtilis

Expression of the major intracellular serine protease (ISP-1) gene of Bacillus subtilis was studied by using a translational fusion plasmid in which the isp promoter region was fused to the lacZ gene. beta-Galactosidase activity, used to measure transcription from the isp promoter, was produced immediately after the end of exponential growth, whereas intracellular protease activity was not detected until 4 h later. These results are consistent with a previous suggestion that ISP-1 initially accumulates in the cell in an enzymatically inactive form. ISP-1 activity was detected in all of the sporulation-deficient strains examined, and the amount of protease activity always corresponded to the amount of beta-galactosidase activity. These results indicate that the activation of ISP-1 is not dependent on a sporulation-specific gene product. Expression of ISP-1 is regulated by a number of mutations known to affect the expression of extracellular enzymes. In sacU(h) and sacQ(h) mutants, the expression of ISP-1 was 10-fold higher than in the wild-type strain. In catA, hpr, and scoC strains, expression of ISP was stimulated two- to threefold, whereas in sacU mutants the expression of ISP-1 was reduced to less than 10% of the wild-type level. The temporal expression and activation of ISP-1 was not affected by any of these mutations. This is the first evidence that the expression of a native intracellular protein is affected by these hyperproduction mutations.

Elastase-producing microorganisms in horse lungs: their possible role in the pathogenesis of chronic pulmonary disease in the horse

Seventeen out of 21 horses had pulmonary microbial organisms which reached considerable numbers in seven cases. Elastase-producing microorganisms from the environment (Streptomyces species and to a lesser extent Bacillus species) constituted 22 per cent to 99 per cent (mean 79 per cent) of the total growth. There was a considerable number of microorganisms with in vitro-produced elastases which were not or only slightly affected by horse serum. There was no correlation between numbers of organisms and pulmonary histopathological findings thus the significance of these microorganisms in the pathogenesis of alveolar emphysema is unknown. The growth of a strain of Streptomyces collinus/diastatochromogus isolated from the lungs was suppressed by fresh horse serum but not by decomplemented horse serum. Complement activation in response to this organism could contribute to airway inflammation through the production of mediators.