The thermophilic fermentation of cellulosic material is generally regarded-as a result of the combined action of several species of bacteria, some of which attack the cellulose and others the sugars formed from the breakdown of the cellulose. Much effort has been spent on attempts to isolate the cellulose fermenters but very little attention has been paid to the associated sugar-fermenting organisms. Snieszko and Kimball (1933) isolated and described two types of such bacteria but gave no chemical data on the fermentation products formed. It, therefore, seemed desirable to make such a study. EXPERIMENTAL Medium and cultures The following medium was used in most of the experiments: Medium 1 NaNHiHPO4........
Although the nutritional factors essential for yeast growth have been extensively studied, the yeast cell yields obtained on media of known composition have always been much lower than those attainable on a natural medium. In the present investigation yeast nutritional requirements have been studied under aeration conditions shown to be optimal. A synthetic medium has been found on which yields equal to those attainable on natural media can be obtained. A number of papers on the nutritional requirements of yeast have appeared since the review of Williams (1941). Leonian and Lilly (1942), Burkholder (1943), Burkholder, McVeigh, and Moyer (1944), and Thorne (1945) have presented data on the vitamin and nitrogen requirements of yeast. Joslyn (1941) has reviewed yeast mineral metabolism. De Becze and Liebmann (1944) and Singh, Agarwal, and Peterson (1948) have discussed the effects of aeration on yeast yields. METHODS Fermentation method8. The strains of yeast used in this work were obtained from Professor McCoy of the Agricultural Bacteriology Department of the University of Wisconsin. Saccharomyces cerevisiae y-30, which has been used for the major part of this work, is a single cell isolate from a commercial bakers' yeast. The 500-ml Erlenmeyer flasks that were used for studying yeast growth were plugged with cotton and sterilized. Twenty-five ml of the fermentation medium, previously sterilized at 120 C for 30 minutes, were transferred aseptically to each sterile flask just before inoculation. The inoculum was prepared by making two consecutive 18-hour transfers in basal medium. In the case of the mineral studies, the element to be tested for was removed from the basal medium. If the experiment warranted, as in the study of growth factor requirements, the yeast was washed once and then resuspended in sterile distilled water before use as inoculum. Five-hundredths ml of the second transfer were used to inoculate each experimental flask. This volume contained approximately 0.15 mg of dry yeast except when the growth of the inoculum was decreased because of the absence of some metal. After inoculation the flasks were shaken for 24 hours at 30 C on a Gump rotary shaker that described a 2k-inch diameter circle at 253 rpm. In mineral re-1 Published with the approval of the Director of the Wisconsin Agricultural Experiment Station. This investigation was supported in part by a grant from Standard Brands, Inc.,
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