Properties of Bacillus megaterium and Bacillus subtilis Mutants Which Lack theProtease That Degrades Small, Acid-Soluble Proteins during Spore Germination

摘要

During germination of spores of Bacillus species the degradation of the spore'spool of small, acid-soluble proteins (SASP) is initiated by a protease termed GPR, the product of the gpr gene. Bacillus megaterium and B. subtilis mutants with an inactivated gpr gene grew, sporulated, and triggered spore germination as did gpr+ strains. However, SASP degradation was very slow during germination of gpr mutant spores, and in rich media the time taken for spores to return to vegetative growth (defined as outgrowth) was much longer in gpr than in gpr+ spores. Not surprisingly, gpr spores had much lower rates of RNA and protein synthesis during outgrowth than did gpr+ spores, although both types of spores had similar levels of ATP. The rapid decrease in the number of negative supertwists in plasmid DNA seen during germination of gpr+ spores was also much slower in gpr spores. Additionally, UV irradiation of gpr B. subtilis spores early in germination generated significant amounts of spore photoproduct and only small amounts of thymine dimers (TT); in contrast UV irradiation of germinated gpr+ spores generated almost no spore photoproduct and three to four times more TT. Consequently, germinated gpr spores were more UV resistant than germinated gpr+ spores. Strikingly, the slow outgrowth phenotype of B. subtilis gpr spores was suppressed by the absence of major a/B-type SASP. These data suggest that (1) Jo-type SASP remain bound to much, although not all, of the chromosome in germinated gpr spores; (2) the a/B-type SASP bound to the chromosome in gpr spores alter this DNA's topology and UV photochemistry; and (3) the presence of a/B-type SASP on the chromosome is detrimental to normal spore outgrowth.