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Ethanol production by thermophilic bacteria: biochemical basis for ethanol and hydrogen tolerance in Clostridium thermohydrosulfuricum
Author(s) -
Robert W. Lovitt,
GwoJenn Shen,
J. G. Zeikus
Publication year - 1988
Publication title -
journal of bacteriology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.652
H-Index - 246
eISSN - 1067-8832
pISSN - 0021-9193
DOI - 10.1128/jb.170.6.2809-2815.1988
Subject(s) - alcohol dehydrogenase , fermentation , biochemistry , ethanol , biology , clostridium , strain (injury) , dehydrogenase , nad+ kinase , lactate dehydrogenase , hydrogenase , ethanol fuel , bacteria , enzyme , genetics , anatomy
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.

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