ALDONIC ACID METABOLISM I. Streptococcus faecalis

Abstract

Gluconic acid serves as an energy source for the growth of the homofermentative coccus S. faecalis strain 10C1. Comparison of cell yield per moles of glucose and of gluconate as energy source showed them to be roughly equivalent, suggesting that the gluconate fermentation approaches the Embden-Meyerhof pathway in energy yield to the cells. Calculations of phosphorylation energy available from known reactions in the pathways indicated by the products of fermentation account for a net of only 1.3 moles of energy-rich phosphate per mole of gluconate, thus suggesting a need for further clarification. Induction of gluconate fermentation results in simultaneous adaptation to 2-keto- but not to 5-ketogluconate fermentation. Gluconate fermentation, at acid pH, yields 0.5 mole CO2 and 1.5 moles lactate. In the presence of 10-3 [image]arsenite, the CO2 yield remains 0.5 mole and the lactate yield is increased to 1.75 mole per mole of gluconate. These data, and the product labeling during fermentation of gluconate-1-C14, -2-C14, and -6-C14, suggest complete conversion of gluconate to CO2 and lactate via a combined pentose phosphate and Entner-Doudoroff pathways.