Mixed-Culture Interactions I. Commensalism of Proteus vulgaris with Saccharomyces cerevisiae in Continuous Culture

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Shindala, Adnan (Virginia Polytechnic Institute, Blacksburg), Henry R. Bungay III, Noel R. Krieg, and Kathleen Culbert. Mixed-culture interactions. I. Commensalism of Proteus vulgaris with Saccharomyces cerevisiae in continuous culture. J. Bacteriol. 89:693–696. 1965.—A chemically defined medium was selected which supported the growth of Saccharomyces cerevisiae, but not Proteus vulgaris, in pure culture; however, P. vulgaris grew in mixed culture with the yeast. Steady-state populations of each organism in mixed culture at various dilution rates were enumerated with a Coulter electronic counter. The size differences in the organisms permitted easy resolution. An essential niacinlike factor elaborated by the yeast and required by the bacterium caused a dependence of the bacterium on the growth of the yeast. At high dilution rates causing wash-out, the bacterial population continued to reflect changes in the numbers of yeast. The numbers of S. cerevisiae were identical in pure culture or in mixed culture; thus, the interaction is a true commensalism. A single addition of niacin or related compound was made to a steady-state mixed culture, and the dependence of the bacterium on the yeast was upset. The numbers of the bacteria rose, causing a decrease in the yeast population, until continued pumping diluted the added niacin and restored the initial steady state.

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