Both Escherichia coli (E. coli) and Salmonella enterica serovar Typhimurium (S. Typhimurium) have a tdc operon that encodes enzymes involved in a metabolic pathway for the degradation of L-serine and L-threonine. However, S. Typhimurium does not have the tdcR gene, which is a positive regulator in E. coli. In the present study, transcriptional analysis revealed that tdcA expression in E. coli is higher under anaerobic than aerobic growth conditions, but the opposite is true in S. Typhimurium. Interestingly, a tdcR mutant strain of E. coli showed a similar expression pattern to that observed in S. Typhimurium and was also induced by anaerobic shock. These results suggest that the induction of tdcA expression by anaerobic conditions is observable when tdcA expression is low owing to the absence of TdcR.