UTILIZATION OF AROMATIC AMINO ACIDS BY HYDROGENOMONAS FACILIS

Abstract

DeCicco , B. T. (Rutgers, The State University, New Brunswick, N.J.), and W. W. Umbreit . Utilization of aromatic amino acids by Hydrogenomonas facilis . J. Bacteriol. 88: 1590–1594. 1964.—An auxotrophic mutant of Hydrogenomonas facilis was isolated which requires tryptophan, phenylalanine, and p -aminobenzoic acid (PABA) for growth. With glucose as the main carbon and energy source, the quantitative requirements for tryptophan and PABA were at normal microgram levels, but the requirement for phenylalanine was very large and approached substrate concentrations. The large phenylalanine requirement is due to a rapid oxidation and degradation of phenylalanine by the mutant. The utilization of both phenylalanine and glucose is adaptive, and the presence of phenylalanine partially inhibits the induction of the glucose-utilizing system. Wild-type H. facilis can utilize either phenylalanine or tyrosine for growth. Tracer studies indicated that during growth on phenylalanine, the aromatic ring is opened and degraded. Wild-type cells grown on either phenylalanine or tyrosine can oxidize phenylalanine, tyrosine, or phenylpyruvate without a lag. Another inducible pathway enables H. facilis to utilize either quinate or 3,4-dihydroxybenzoate for growth, and sequential adaptation studies revealed that quinate is converted to 3,4-dihydroxybenzoate during its degradation. Mutants may be obtained which can also utilize 2,5-dihydroxybenzoate for growth.