Biological Role of Gramicidin S in Spore Functions

Abstract

Gramicidin‐S‐negative mutants of Bacillus brevis ATCC9999 have been isolated with a remarkly higher yield after ethidium bromide or acridine orange treatment, than after N ‐methyl‐ N' ‐nitro‐ N ‐nitrosoguanidine treatment. Four (MIV, Sm r 170, R5 and EB 16) of 38 isolated mutants were characterized with respect to the lesion in gramicidin‐S‐synthesizing activity. The mutants sporulate to the same extent as the parental strain except mutant Sm r 170 which sporulates less. However, mutant spores were more heat‐sensitive and possessed a reduced level of dipicolinic acid content. No significant difference was observed in the germination time of wild‐type and mutant spores. All spores germinated after 80–110 min, but the outgrowth time was different: all gramicidin‐S‐negative mutants grew out immediatly after germination whereas wild‐type spores required a lag period of 9–10 h. When the mutants were allowed to sporulate in the presence of gramicidin S, the spores were found to be heat‐resistant and their outgrowth postponed to the same period as the parent spores. The addition of gramicidin also eliminated the deficiency of dipicolinic acid. A new class of gramicidin‐S‐negative mutant, R5, which only activates L ‐valine and L ‐leucine, is described. A possible biological function of gramicidin S in the heat‐resistance and in the timing of spore outgrowth is discussed.