"Acidic pH-sensitive mutants": acid resistance in acetic acid bacteria

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1) Fifteen strains of acidic pH-sensitive mutants were isolated from Gluconobacter cerinus IFO 3267 by treatment of nitrosoguanidine, followed by the conventional replica method. The isolated strains showed the properties of the dissolution of <CaCO_3> , the absence of oxidizing lactate and acetate to carbon dioxide and water and the presence of ubiquinone-10. The cell-free extracts of the strains had the respective enzyme activities of membrane-bound glucose dehydrogenase, 5-ketofructose reductase, mambrane-bound mannitol dehydrogenase and so on.2) The growth of all the mutant strains was negative at pH 4.0. However, the better growth was observed at and near the neutral pH. Of the isolated mutant strains, the six strains of PSM-51, PSM-64, PSM-104, PSM-110, PSM-120 and PSM-121 were especially sensitive to the acid and alkaline pHs. They showed maximal growth at pH 6.0. However, in the both sides of the neutral.pH, i.e., pH 5.0 and pH 7.0, their growth gradually decreased.3) The membr … More ane lipid composition of all the mutant strains were analyzed. Three mutant strains, PSM-51, PSM-120 and PSM-121 were different in phospholipid composition compared with the parent strain. Firstly, PSM-51 was increased in the content of phosphatidylethanolamine from two to three times and decreased in that of phosphatidylcholine from 25 to 30%. Secondly, other two mutant strains, PSM-120 and PSM-121 had 60% phospholipid content compared with the parent strain.4) The biosynthetic pathway of phosphatidylcholine from phosphatidylethanolamine was analyzed by using the intact cells and the cell-free extract of PSM-51 with [methyl- <^(14)C> ]methionine. The activities of the mutant strain was 60% in the intact cells and the same in the cell-free extract compared with the parent strain.5) The intracellular and extracellular pHs of the mutant and the parent strains were measured across the cell membrane with a radioactive weak organic acid, 5,5-dimethyl[2- <^(14)C> ]oxazolidine-2,4-dione. In the parent strain, the intracellular pH was not affected by the alteration of the extracellular pH, i.e., from pH 3.0 to pH 7.0: the intracellular pH was almost constantly retained in the pH range of 6.0-6.5. On the other hand, the intracellular pH of all the mutant strains decreased below pH 5.9 when incubated at pH 4.0. At the extracellular pH 3.0, the intracellular pHs of the mutant strains were not able to be measured. The intracellular pH of the parent strain was retained at pH 6.03. Less