AROMATIC BIOSYNTHESIS IV

Abstract

Mutants of Escherichia coli, Aerobacter aerogenes, Salmonella typhimurium, and Bacillus subtilis that require 2, 3, 4, or 5 aromatic compounds are blocked in the synthesis of precursors common to all 5 of the compounds. The multiplicity of the requirement depends on the completeness of the block. Increasing inability to synthesize the common precursors leads to successive growth requirements in the following order tyrosine, phenylalanine, tryptophan, p-aminobenzoic acid, and finally p-hydroxybenzoic acid. The recognition of these incomplete blocks and of this preferential synthesis reconciles the growth requirements of the 62 available multiple aromatic auxotrophs with their accumulation and utilization of intermediates. A general scheme of aromatic biosynthesis, therefore, can be constructed, including the common precursors compound W, 5-dehydroshikimic acid, and shikimic acid. Since tyrosine, phenylalanine, and tryptophan cannot replace each other as growth factors for the quintuple auxotrophs, it is concluded that the bacterial species studied, in contrast to the rat, cannot utilize any one of these amino acids as a precursor of another.