Propionate metabolism

The data presented are concerned with factors regulating adaptation of Escherichia coli to growth on propionate. A mutant strain of E. coli E-26 was employed; this mutant grows on acetate and on a number of other substrates, but is unable to initiate growth when propionate is the sole source of carbon. The mutant possesses a functional tricarboxylic acid cycle and glyoxylate bypass; is able to oxidize propionate to acetate; but is unable to effect sufficient formation of C 4 acids required for initiation of growth on propionate. This deficiency can be overcome by the addition of either succinate or HCO 3 − to propionate media. It is proposed that the mutant is deficient in one or more carboxylation reactions, since such cells possess a markedly decreased capacity to incorporate 14 CO 2 into cell material. It is further suggested that carboxylation reactions are most active during initiation of growth on propionate and decline as growth proceeds.