| Budget Amount *help |
¥2,100,000 (Direct Cost: ¥2,100,000)
Fiscal Year 1993: ¥1,100,000 (Direct Cost: ¥1,100,000)
Fiscal Year 1992: ¥1,000,000 (Direct Cost: ¥1,000,000)
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| Research Abstract |
Nicroorganisms are good materials for clarifying the adaptationof living things to ensironmental changes, since their habitat encompasses all surface of the earth. We have studied the bacterial adaptation to change in environmental pH, and found that the change in cellular metabolisms to ones resistant to alkaline pH is essential for the adaptation to an alkaline pH, rather than the maintenance of the neutral cytoplasm. In the present study, we have carried out biochemical and genetical studies of genes which are essential for growth in an alkaline medium, and following results have been obtained. (1) In desagreenent with the previous propasal that Na^+/H^+ antiporter maintains the neutral cytoplasm of E.coli growing in an alkaline medium, it is suggested that the physiological functionof this antiporter is to maintain the internal sodium ion concentration at a low level in an alkaline medium as well as neutral and acidic madia. (2) We have found that ChaA, which was originally reported to be a Ca^<++>/ antiporter, is a third system for sodium ion extrusion fuctioning at an alkaline pH.Our present data suggest that E.coli uses NhaB to extrude sodium ion in neutral and acidec media, and that NhaA and ChaA are used at an alkaline pH.(3) We have isolated mutants which are unable to grow at an alkaline pH, even if the medium level of sodium ion is low. It is therefore suggested that, in addition to nhaA and chaA, E.cli has other genes fumctioning at a high pH.
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