Delayed inducibility of sulphite reductase in cysM mutants of Salmonella typhimurium under anaerobic conditions.

Salmonella typhimurium cysM mutants grow at a normal rate under aerobic conditions, but only after a lag period under anaerobic conditions. No difference in the induction of two cysteine biosynthetic enzymes--sulphite reductase and O-acetyl-L-serine sulphydrylase--in wild-type, cysK and cysM strains was observed under aerobic conditions. Under anaerobic conditions, however, the cysM strain differed from the others in showing a long delay in the induction of sulphite reductase. These observations are consistent with the assumption that the observed growth delay of the cysM mutant under anaerobic conditions is the result of abnormalities in the regulation of sulphite reductase.