MEDIUM SUPPLEMENTATION WITHL- ANDD-AMINO ACIDS RELATIVE TO GROWTH AND EFFICIENCY OF RHIZOBIUM MELILOTI

Abstract

Five strains of Rhizobium meliloti serially cultivated on a basal yeast water mannitol mineral salts medium supplemented with increments of nine amino acids, respectively, produced ellipsoidal, bacteroidal, and elongated cell forms. Colonies produced on media containing D-amino acids and glycine were smaller and less opalescent than were those on the basal medium. Growth of two strains on media supplemented with the L-isomers of alanine, histidine, and phenylalanine, respectively, exceeded that in media to which the D-isomers of these amino acids were added. Growth was negative or sparse in the basal medium supplemented with 0.075% L-cysteine. Serial cultivation in media containing increments of D-cysteine, D-alanine, D-phenylalanine, and glycine produced the maximum loss in nitrogen-fixing ability; L-alanine and L-histidine were the least deleterious. Four strains became ineffective after serial cultivation on at least two of the nine amino acid media. The infective and nitrogen-fixing properties of an ineffective strain were unchanged after cultivation in amino acid supplemented media.