Mutant strains of Escherichia coli K-12 unable to form ubiquinone.

A strain of Escherichia coli was isolated which was unable to form ubiquinone. This mutant was obtained by selecting strains unable to grow on malate as sole source of carbon. Such strains were further screened by examination of the quinone content of cells grown on a glucose medium. A mutant unable to form vitamin K was also isolated by this procedure. A genetic analysis of the ubiquinoneless strain showed that it possessed two mutations affecting ubiquinone biosynthesis.