The ppa gene for inorganic pyrophosphatase is essential for the growth of Escherichia coli. A recombinant with a chromosomal ppa::Kanr lesion and a temperature-sensitive replicon with a ppa+ gene showed a temperature-sensitive growth phenotype, and a mutant with the sole ppa+ gene under control of the lac promoter showed inducer-dependent growth. When the lacp-ppa mutant was subcultured without inducer, the pyrophosphatase level decreased, the PPi level increased, and growth stopped. Cellular PPi reached 16 mM about 6 h after growth arrest without loss of cell viability.