Pathways of pyruvate metabolism and energetics of growth of Brochothrix thermosphacta

Brochothrix thermosphacta, a psychrophilic, facultative anaerobe, exhibited homolactic fermentation under anaerobic conditions in the presence of excess glucose. In glucose-limited chemostat culture (on synthetic medium), ethanol, acetate, formate and lactate were formed. Formation of ethanol and acetate was accounted for by the formate concentrations in culture filtrates. Acetate, formate and ethanol formation was enhanced at low growth rates in chemostat culture. O2-limited chemostat studies indicated that formate formation was inhibited by oxygen (<0.2 μM) and studies with a variant, strain 301, which lacked pyruvate dehydrogenase activity, showed that cell culture in basal medium did not occur at O2 tensions greater than that preventing formate production in the wild-type strain. The data are consistent with stimulation of pyruvate formate lyase activity by glucose limitation, possibly because of decreased concentrations of glycolytic intermediates.