Mutants ofBacillus stearothermophiluslacking NAD-linked l-lactate dehydrogenase

Abstract

Bacillus stearothermophilus produces low levels of ethanol following fermentation of glucose at temperatures in excess of 60°C. A major by‐product is l‐lactic acid. To improve ethanol yields mutants of this organism were isolated which lacked NAD‐linked l‐lactate dehydrogenase, the enzyme responsible for lactic acid production. This was achieved by selection for resistance to a suicide substrate, fluoropyruvate. Such mutants no longer produced lactic acid and yields of ethanol from glucose were increased by at least a factor of two.

Growth of a lactate dehydrogenase deficient mutant of bacillus stearothermophilus in continuous culture

“…Bacillus stearothermophilus is a well characterized thermophile and since the time when it was first suggested that it might be a suitable candidate for industrial ethanol production, [5], significant advances have been made in obtaining high ethanol yielding mutants. It was isolated by selecting for suicide substrate resistance [6] and since its isolation has been extensively studied [7,8,91. It was isolated by selecting for suicide substrate resistance [6] and since its isolation has been extensively studied [7,8,91.…”