Nucleotide sequence of the sspE genes coding for gamma-type small, acid-soluble spore proteins from the round-spore-forming bacteria Bacillus aminovorans, Sporosarcina halophila and S. ureae

Extremely variable conservation of γ-type small, acid-soluble proteins from spores of some species in the bacterial order Bacillales

γ-Type small, acid-soluble spore proteins (SASP) are the most abundant proteins in spores of at least some members of the bacterial order Bacillales, yet they remain an enigma from both functional and phylogenetic perspectives. Current work has shown that the γ-type SASP or their coding genes (sspE genes) are present in most spore-forming members of Bacillales, including at least some members of the Paenibacillus genus, although they are apparently absent from Clostridiales species. We have applied a new method of searching for sspE genes, which now appear to also be absent from a clade of Bacillales species that includes Alicyclobacillus acidocaldarius and Bacillus tusciae. In addition, no γ-type SASP were found in A. acidocaldarius spores, although several of the DNA-binding α/β-type SASP were present. These findings have elucidated the phylogenetic origin of the sspE gene, and this may help in determining the precise function of γ-type SASP.

Studies on the mechanism of the osmoresistance of spores of Bacillus subtilis

AIMS

To determine the reason that spores of Bacillus species, in particular Bacillus subtilis, are able to form colonies with high efficiency on media with very high salt concentrations.

METHODS AND RESULTS

Spores of various Bacillus species have a significantly higher plating efficiency on media with high salt concentration (termed osmoresistance) than do log or stationary phase cells. This spore osmoresistance is higher on richer media. Bacillus subtilis spores lacking various small, acid-soluble spore proteins (SASP) were generally significantly less osmoresistant than were wild-type spores, as shown previously (Ruzal et al. 1994). Other results included: (a) spore osmoresistance varied significantly between species; (b) the osmoresistance of spores lacking SASP was not restored well by amino acid osmolytes added to plating media, but was completely restored by glucose; (c) the osmoresistance of spores lacking SASP was restored upon brief germination in the absence of salt in a process that did not require protein synthesis; (d) significant amounts of amino acids generated by SASP degradation were retained within spores upon germination in a medium with high but not low salt; (e) slowing but not abolishing SASP degradation by loss of the SASP-specific germination protease (GPR) did not affect spore osmoresistance; (f) sporulation at higher temperatures produced less osmoresistant spores; and (g) spore osmoresistance was not decreased markedly by the absence of the stress sigma factor for RNA polymerase, sigmaB.

CONCLUSIONS

Spore osmoresistance appears as a result of three major factors: (1) specific characteristics of spores and cells of individual species; (2) the precise sporulation conditions that produce the spores; and (3) sufficient energy generation by the germinating and outgrowing spore to allow the spore to adapt to conditions of high osmotic strength; the substrates for this energy generation can come from either the endogenous generation of amino acids by SASP degradation or from the spore's environment, in the form of a readily taken up and metabolized energy source such as glucose. SIGNFICANCE AND IMPACT OF STUDY: These results provide information on the mechanisms of spore osmoresistance, a spore property that can be of major applied significance given the use of high osmotic strength with or without high salt as a means of food preservation.