Amino acid transport in Azotobacter vinelandii: implications of nonavailability of amino acid auxotrophs

Abstract

Amino acid uptake studies in Azotobacter vinelandii were undertaken to determine whether absence of uptake could be a possible reason for the difficulty in isolating auxotrophic mutants in this organism. A. vinelandii cells were found to be capable of transporting amino acids via an active mechanism. Kinetic studies with four amino acids and respiratory inhibitors confirmed the presence of energy dependent amino acid uptake systems. The K_t values for L-glutamate, L-alanine, L-cysteine and L-lysine were 10, 23, 91 and 233 µM, respectively. Incorporation of amino acids into trichloroacetic acid precipitable fractions further confirmed that the transported amino acids were incorporated into proteins. Thus the lack of at least some classes of amino acid auxotrophs of A. vinelandii is probably not because of poor transport of amino acids.