Abstract
The characteristics of the pH-dependent biotin requirement of Lipomyces starkeyi IAM 4753 were investigated in growing cells. Microbiological and radioisotope assays were employed to measure biotin content in the cells and in the medium. This yeast exhibited a strict biotin requirement in a medium with a pH ranging from 5.5 to 6.5. The minimum amount of biotin needed for normal growth in the bufferized medium with a pH of 6.0 was 0.1μg/liter. The maximum growth rate was observed when 0.5μg or more of biotin was added to the bufferized medium with a pH of 6.0; cellular radioactivity increased gradually accompanied by an increase of true biotin in the cells until the concentration of true biotin in the medium became undetectable. A part of the biotin added was degraded during the growth. Cellular biotin content remained constant for about 10hr followed by a gradual increase. The reincrease of the cellular true biotin content began at a point when the pH of the medium was below 5.5. From these results, it was concluded that the initiation of biotin biosynthesis in L. starkeyi IAM 4753 depends on the pH value of the medium.
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