Vitamin K-deficient Mutants of Bacteria

Abstract

AUXOTROPHIC mutants of bacteria with various metabolic blocks have proved useful for the elucidation of intermediary steps in biosynthetic pathways¹. Until recently this approach has not been applied to the biosynthesis of K vitamins (menaquinones), chiefly because of the lack of adequate vitamin K-deficient mutants² which would accumulate significant intermediary metabolites. We have isolated some menaphthone-requiring, small-colony mutants of Staphylococcus aureus by selection with neomycin³ and found that they grow and respire normally on media supplemented with menadione. This could be attributed to bridging of the main electron transport chain by menadione, which is known to be capable of by-passing flavin, vitamin K2 and cytochrome b (ref. 4). If so, the mutants stimulated by menadione might equally represent flavin-deficient, vitamin K-deficient, or cytochrome 6-deficient mutants. Alternatively, if menadione is an intermediate in the biosynthesis of K vitamins, these mutants may simply be of the vitamin K-deficient type. The biosynthesis of menaquinones up to chorismic acid follows the common pathway of aromatic amino-acids², so that some of the vitamin K-deficient mutants stimulated by menadione might be stimulated by shikimic acid as well, provided that the latter can penetrate the bacterial Cell.