Escherichia coli mutants lacking NADH dehydrogenase I have a competitive disadvantage in stationary phase.

We have previously characterized mutant strains of Escherichia coli that are able to take over stationary-phase cultures. Here we describe two insertion mutations that prevent such strains from expressing this phenotype. Both insertions were mapped to min 51, and sequence analysis revealed that both mutated genes encode proteins homologous to subunits of mitochondrial NADH dehydrogenase I. Crude extracts prepared from both mutant strains were able to oxidize NADH but lacked the enzymatic activity needed to oxidize deamino-NADH, a substrate specific for NADH dehydrogenase I. This is the first identification of genes encoding subunits of NADH dehydrogenase I in E. coli. The significance of the inability of these mutant strains to compete in stationary-phase cultures is discussed.