End products of glucose fermentation by Brochothrix thermosphacta

Abstract

Anaerobically, B. thermosphacta fermented glucose primarily to L-lactate, acetate, formate, and ethanol. The ratio of these end products varied with growth conditions. Both the presence of acetate and formate and a pH below about 6 increased L-lactate production from glucose. Small amounts of butane-2,3-diol were also produced when the pH of the culture was low (≤ 5.5) or when acetate was added to the growth medium. Radioactive label from [1-14C]acetate was incorporated into ethanol and L-lactate, implying reversibility of pyruvate-formate lyase. In crude extracts, the following enzymes involved in pyruvate metabolism were demonstrated: lactate dehydrogenase, phosphotransacetylase, acetate kinase, acetaldehyde dehydrogenase (coenzyme A acetylating), ethanol dehydrogenase, pH 6 acetolactate-forming enzyme, and diacetyl (acetoin) reductase. The lactate dehydrogenase did not require fructose-1,6-diphosphate or Mn2+ for activity.