THE UTILIZATION OF PURINES, PYRIMIDINES, AND INORGANIC NITROGENOUS COMPOUNDS BY EFFECTIVE AND INEFFECTIVE STRAINS OF RHIZOBIUM MELILOTI

Abstract

Ammonium chloride was not utilized by three strains of Rhizobium meliloti as the sole source of nitrogen in a sucrose medium, unless either amino or certain non-nitrogenous carboxylic acids were also present. This was also essentially true for the utilization of nitrate, nitrite, purines, and pyrimidines, all of which are potentially able to form ammonia. These results may be interpreted on the assumption that washed cells of alfalfa – sweet clover rhizobia require, for growth initiation in a nitrogen-free medium, either preformed amino acids or compounds such as ammonia and certain carboxylic acids from which amino acids can be synthesized. Since α-ketoglutarate was extremely active in promoting growth in a medium containing ammonium chloride it was implied that the ammonia may be fixed by L-glutamic acid dehydrogenase activity, especially since this particular enzyme was located in these organisms. No aspartase activity could be demonstrated. The ineffective strain differed from the effective strains in that it was unable to use purines or pyrimidines as accessory nitrogen sources in amino acid media. This was a result of strain variation and it was not coupled with the state of ineffectiveness itself. A synthetic medium has been formulated for further growth studies on washed Rhizobium cells and for investigations on auxotrophic mutants of these bacteria.