Ethanol production by thermophilic bacteria: biochemical basis for ethanol and hydrogen tolerance in Clostridium thermohydrosulfuricum.
The metabolic and enzymatic bases for growth tolerance to ethanol (4%) and H2 (2 atm [1 atm = 101.29 kPa]) fermentation products in Clostridium thermohydrosulfuricum were compared in a sensitive wild-type strain and an insensitive alcohol-adapted strain. In the wild-type strain, ethanol (4%) and H2 (2 atm) inhibited glucose but not pyruvate fermentation parameters (growth and end product formation). Inhibition of glucose fermentation by ethanol (4%) in the wild-type strain was reversed by addition of acetone (1%), which lowered H2 and ethanol production while increasing isopropanol and acetate production. Pulsing cells grown in continuous culture on glucose with 5% ethanol or 1 atm of H2 significantly raised the NADH/NAD ratio in the wild-type strain but not in the alcohol-adapted strain. Analysis of key oxidoreductases demonstrated that the alcohol-adapted strain lacked detectable levels of reduced ferredoxin-linked NAD reductase and NAD-linked alcohol dehydrogenase activities which were present in the wild-type strain. Differences in the glucose fermentation product ratios of the two strains were related to differences in lactate dehydrogenase and hydrogenase levels and sensitivity of glyceraldehyde 3-phosphate dehydrogenase activity to NADH inhibition. A biochemical model is proposed which describes a common enzymatic mechanism for growth tolerance of thermoanaerobes to moderate concentrations of both ethanol and hydrogen.
Lovitt
R W
RW
Michigan Biotechnology Institute, Lansing 48910.
Shen
G J
GJ
Zeikus
J G
JG
D003013:Clostridium / Q000378:metabolism*; D000431:Ethanol / Q000096:biosynthesis*; D005285:Fermentation; D005987:Glyceraldehyde-3-Phosphate Dehydrogenases / Q000378:metabolism; D006859:Hydrogen / Q000378:metabolism*; D009243:NAD / Q000378:metabolism
D009243:NAD; D000431:Ethanol; D006859:Hydrogen; D005987:Glyceraldehyde-3-Phosphate Dehydrogenases