Competition among Amino Acids for Incorporation into Methylococcus capsulatus

SUMMARY: Amino acid uptake by Methylococcus capsulatus was found to be effected by a transport system common to a wide range of amino acids. Some correlation existed between the amount of an amino acid incorporated and its effectiveness as a competitor against other amino acids, thus indicating different affinities among amino acids for the transport system. Uptake of some amino acids (e.g. the aromatic group and lysine) by an additional mechanism(s) is also suggested. Relief of threonine-inhibition of growth by metabolically related and unrelated amino acids is explained in terms of inhibition by other amino acids of the accumulation into the organisms of bacteriostatic levels of threonine. The threonine-resistant mutants isolated had decreased capacities to incorporate threonine and all the other amino acids tested.