Designed deletion and insertion were constructed on plasmids into nhaA gene, coding a Na+/h+ antiporter A(NhaA) of Escherichia coli. The chromosomal nhaA gene was replaced with the mutated genes, resulting deletion and insertion mutants. The designed mutations in chromosomal nhaA genes of the mutants were confirmed by genetic analysis and after retrieval of the chromosomal mutations on plasmids. The deletion and insertion mutants displayed sodium (lithium) and alkalinity sensitive phenotypes. The Na+/H+ antiport activity of the mutants is not significantly altered, due to another Na+/H+ antiporter (NhaB) in E. coli (Seo, 1992, Kor. J. Microbiol. 30: 269-277).