2-KETOGLUCONATE FERMENTATION BY STREPTOCOCCUS FAECALIS

Abstract

Goddard , J. L. (University of Oklahoma School of Medicine, Oklahoma City), and J. R. Sokatch . 2-Ketogluconate fermentation by Streptococcus faecalis . J. Bacteriol. 87: 844–851. 1964.— Streptococcus faecalis 10Cl did not grow with 2-ketogluconate alone as an energy source, but did grow when gluconate was added. More growth was obtained than could be accounted for by the gluconate alone. The requirement for gluconate in the stimulation of growth on 2-ketogluconate was found to be stoichiometric, not catalytic. Glucose did not replace gluconate in this phenomenon, apparently owing to the repression of the 2-ketogluconate pathway by glucose. Resting cells grown on a combination of gluconate and 2-ketogluconate did ferment 2-ketogluconate without added gluconate. Fermentation balance studies with resting cells detected the following products in moles (per mole of 2-ketogluconate): carbon dioxide, 0.98; lactic acid, 0.19; formic acid, 1.42; acetic acid, 0.70; and ethanol, 0.42. 2-Ketogluconate- 1-C 14 and - 2-C 14 were prepared and fermented. The data were interpreted to show that 90% of the substrate was decarboxylated to carbon dioxide and pentose phosphate. Pentose phosphate was then fermented to pyruvate through the sedoheptulose diphosphate variation of the pentose phosphate pathway found in this organism. The other 10% of the substrate was converted to pyruvate by way of the Entner-Doudoroff pathway. Calculations of the energy available by the above combination of pathways indicated that about 2.3 moles of adenosine triphosphate per mole of 2-ketogluconate could be obtained if the energy available in acetate formation is conserved through the acetokinase reaction.