Genetical and molecular studies on gerM, a new developmental locus of Bacillus subtilis

A transposon Tn917 insertion between gerE and ilvB has identified a new developmental locus, gerM, in Bacillus subtilis. gerM96::Tn917 affects both sporulation and germination. DNA on either side of the transposon has been cloned and includes the previously cloned sdhC and gerE loci. gerE terminates 2.1 kb from the end of the transposon. The gerM96::Tn917 mutant is oligosporogenous, yielding approximately 1% of the number of wild-type heat resistant spores in liquid medium and 10% on solid medium. Six hours after the onset of sporulation alkaline phosphatase and glucose dehydrogenase levels were 90% and 7%, respectively, of those of the wild-type. At this time 50% of the mutant cells were still dividing. The occurrence of multiple polar septa and 'pygmy' cells suggested a block at stage II of sporulation. Following addition of germinants, mutant spores prepared on nutrient agar lost heat resistance normally but released slightly less dipicolinic acid than wild-type spores. They also showed only partial loss of optical density, associated with a phase-grey appearance and striations in the cortex suggesting partial degradation. Expression of the gerM gene was monitored by production of beta-galactosidase encoded by a promotorless lacZ gene fused to the gerM96::Tn917 insertion. It occurred 1.5-4 h after commencement of sporulation. Transcription was directed from a promoter on the gerE side of gerM and was unaffected by a mutation in the gerE gene.