Cobaltous ion effect on diauxie

Cobaltous ions extended the duration of the diauxic lag in Escherichia coli K-12. Growth in glucose in the presence of Co(++) was necessary for the effect. Medium in which cells had been grown in the presence of Co(++) produced an extended lag when inoculated with fresh cells and lactose. Valine was found in this medium. Reversal of the extended lag was brought about by addition of l-isoleucine and related l-amino acids, but not by several metal ions. Cobaltous ion does not inhibit beta-galactosidase or the galactoside permease. These results, together with the known growth sensitivity of K-12 to valine, indicate that Co(++) disturbs the normal valine-isoleucine balance.