The anaplerotic fixation of carbon dioxide by Escherichia coli

Abstract

The isolation of a mutant (AB 1622) of Escherichia coli K 12 is described, which differs from its parent organism (AB 1621) in lacking the ability to grow upon glucose, glycerol or pyruvate unless utilizable intermediates of the tricarboxylic acid cycle are also supplied in the growth media; both the mutant and its parent grow readily on acetate as sole carbon source. Washed suspensions of AB 1622 oxidized pyruvate only to the level of acetate, which accumulated; when catalytic quantities of L-malate were also supplied, pyruvate was oxidized further and the extent to which it was oxidized approached that observed with suspensions of the wild-type organisms. These observations suggest that the mutant is unable to effect the net formation of tricarboxylic acid cycle intermediates from pyruvate or phosphopyruvate. Analysis of extracts of the mutant, and of its parent organism, showed that the former lacked phosphopyruvate carboxylase activity (EC 4.1.1.31), although other enzymes capable in theory of catalysing the carboxylation of C 3 -acids were abundant in both extracts. It is thus concluded that the net formation of C 4 -acids through carboxylation of C 3 -precursors is necessarily achieved through the agency of phosphopyruvate carboxylase.