Abstract
A PAPER1 from this laboratory described an improved method for the estimation of Oospora lactis Fres. (formerly known as Oidium lactis) in pressed bakers' yeast, using a medium consisting of ammonium succinate, mineral salts and agar. The method worked well with most yeasts, but one strain (Saccharomyces cerevisiae D.C.L. 557) prevented the growth of visible colonies of Oospora on the above medium. This effect has been further studied, and it has been found that the immediate cause of the inhibition was the presence in the medium of 2 × 10−2 M potassium (as the dihydrogen phosphate). This was demonstrated by excluding potassium from the medium, adding the phosphate as the sodium or ammonium salt. The mould then developed into dense colonies; these were not, however, quite so large as those grown on normal medium (containing potassium) in the absence of yeast. This reduction in size was due to the fact that Oospora required 3 × 10−4 M potassium ions for optimal growth on ammonium succinate, mineral salts, agar medium. When Yeast 557 was present, however, this concentration of potassium, added as sulphate or chloride to the medium (containing sodium or ammonium dihydrogen phosphate), inhibited the growth of the mould. The inhibition was largely overcome by the addition of 5 × 10−4 M aluminium (as ammonium alum) to the normal medium.
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References
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Fleming, W. R., J. Cell. and Comp. Physiol., 49, 129 (1957).
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MILLER, E. Novel Action of Potassium on a Yeast and a Counteraction by Aluminium. Nature 181, 191 (1958). https://doi.org/10.1038/181191a0
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DOI: https://doi.org/10.1038/181191a0
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