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SUMMARY: The power of fermentation by yeast cells was decreased when the cultures were grown in media deficient in any of seven essential growth factors. A rapid increase in the rate of fermentation upon the addition of a growth factor was obtained in every case except that of inositol, where the response was much slower. The absence of a nitrogen source decreased the response to biotin, pantothenic acid or pyridoxin to a much greater extent than to aneurin or nicotinic acid. Differences were noted also in the behaviour of the two pups towards sodium azide, which can be explained on the assumption that biotin, pantothenic acid and pyridoxin affect fermentation only in a relatively indirect manner. The decrease in the power of fermentation produced by pyridoxin deficiency was not observed until the pyridoxin content of the cells was only about one-fifth of the normal. Such yeast showed also an enhanced Pasteur effect. Pyridoxin deficiency produced no decrease in the proportion of glucose assimilated by resting cells. The recognition of the importance of members of the vitamin B complex in the growth of yeast is of long standing. Ample data are now available concerning the requirements of a wide range of species for individual members of the group {e.g. Burkholder, McVeigh & Moyer, 1944; Emery, McLeod & Robinson, 1946), and, of course, some of these requirements form the basis of microbiological assays in common use. It is now known that if one or more of the following compounds or their analogues, biotin, pantothenic acid, pyridoxin, aneurin, nicotinic acid, inositol, or p-aminobenzoic acid, is absent from the growth medium, certain species show a partial or complete restriction of growth. Two of these compounds, aneurin and nicotinic acid, are involved in the generally accepted scheme of alcoholic fermentation. The exact significance of the others is less clearly understood. Few studies have been reported of the direct effect of the lack of essential growth factors upon the power of fermenta- tion. Observations of the effect upon CO, production in a medium otherwise adequate for growth (e,g. Atkin, Schultz & Frey, 1946) may be difficult to interpret, since any differences may result merely from different concentrations of yeast, due to differing growth rates. Williams, Mosher & Rohrman (1936) showed that a deficiency of pantothenic acid diminished the rate of fermenta- tion, and a similar effect resulting from biotin deficiency has also been demon- strated and investigated in some detail (Winder, Burk & du Vigneaud, 1944). The results presented here concern observations made with yeasts deficient in each of the seven above-mentioned essential growth factors. -

The Effect of Growth-factor Deficiencies upon Fermentation of Glucose by Yeasts