Novel alcohol dehydrogenase activity in a mutant of Salmonella able to use ethanol as sole carbon source

We selected a mutant of Salmonella enterica serovar Typhimurium that is capable of growing in air on ethanol as sole carbon and energy source. This adhI mutant expressed high levels of a novel alcohol dehydrogenase (AdhI) that uses ethanol, 1-propanol and 2-propanol as substrates. The fermentative AdhE alcohol dehydrogenase was not expressed aerobically in the adhI mutant. Anaerobically, both the novel AdhI enzyme and the AdhE were expressed simultaneously in the adhI mutant. However, the adhI mutant showed no alteration in the composition of the fermentation products. In addition we found that both the parental Salmonella and its alcohol using adhI mutant expressed substantial levels of a dye-linked aldehyde dehydrogenase that is presumably responsible for conversion of acetaldehyde to acetate. This contrasts with the situation in Escherichia coli where mutants able to grow on ethanol express high aerobic levels of the AdhE enzyme, which performs both the alcohol dehydrogenase and aldehyde dehydrogenase reactions.