Graduate Thesis Or Dissertation
 

Yeast extractives in the nutrition of San Francisco sourdough bacteria (Lactobacillus sanfrancisco)

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  • A laboratory-prepared hot-water extract of yeast is required for vigorous growth of San Francisco sourdough bacteria (Lactobacillus sanfrancisco) in pure culture. This requirement was examined with the goal of determining what is unique about fresh yeast extractives (commercial extractives exhibit much lower growth promoting activity), and which components of fresh yeast extractives are required or stimulatory in the nutrition of these bacteria. Autolysis, the process by which most commercial extractives are prepared, was shown to be less efficient in releasing growth promoting materials for sourdough bacteria than the hot-water extraction procedure used for the preparation of fresh extractives. Essential nutrients supplied by fresh yeast extractives were found to include manganous ion, which the organisms require at a concentration of about 0.2 μg /ml for maximal growth, several vitamins and nucleic acid bases, and a short peptide which accounts for the unique growth promoting activity of this material. The four strains of sourdough organisms examined were found to require thiamine, nicotinic acid, and calcium pantothenate for growth in the test medium employed, while one strain requires, in addition, folic acid. One or more of the nucleic acid bases adenine, guanine, or uracil were demonstrated to be required or stimulatory for all strains. The peptide to which the unique growth promoting activity of fresh yeast extractives may be attributed was isolated and found to contain aspartic acid, cysteine, glutamic acid, glycine, and lysine, with a chain length of about nine residues and a molecular weight of approximately 1,065.
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