好アルカリ性Bacillus ASSC-2の中性pH非感受性突然異変株について

Intracellular pH of an alkalophilic Bacillus sp. ASSC-2 was acidified in the K^+-limited media and could not grow at neutral pH range unless K^+ was added to the media (Oshima & Onoda, 1990). The neutral pH-insensitive mutant, Bacillus ASSC-2NI, was isolated by the treatment with N-methyl-N'-nitro-N-nitrosoguanidine. The mutant could grow in the K^+-limited media even at neutral pH range in the absence of exogenously added K^+, and the intracellular pH was not acidified. The mutant has gained high K^+-transport activity and,consequently, the respiratory activities of the mutant were higher than the parent strain in the absence of added K^+ at neutral pH range. Further, the mutant has retained Na+/H+-antiporter activity at pH 7. The properties of the mutant indicated that if K^+-transport system was actively operating at neutral pH the intracellular pH was protected from acidification by the active Na + /H+-antiport system at neutral pH.