Several strains of the family Rhizobiaceae were tested for their ability to degrade the phosphonate herbicide glyphosate (isopropylamine salt of N-phosphonomethylglycine). AR organisms tested (seven Rhizobium meliloti strains, Rhizobium leguminosarum, Rhizobium galega, Rhizobium trifolii, Agrobacterium rhizogenes, and Agrobacterium tumefaciens) were able to grow on glyphosate as the sole source of phosphorus in the presence of the aromatic amino acids, although growth on glyphosate was not as fast as on Pi. These results suggest that glyphosate degradation ability is widespread in the family Rhizobiaceae. Uptake and metabolism of glyphosate were studied by using R. meliloti 1021. Sarcosine was found to be the immediate breakdown product, indicating that the initial cleavage of glyphosate was at the C-P bond. Therefore, glyphosate breakdown in R. meliloti 1021 is achieved by a C-P lyase activity. Glyphosate (isopropylamine salt of N-phosphonomethylglycine) is the active ingredient in Roundup, a broad-spectrum postemergence herbicide sold worldwide for use in a large number of agricultural crops and industrial sites. It is a potent inhibitor of the enzyme 3-enol-pyruvylshikimate-5phosphate synthase (EPSP synthase, EC 2.5.1.19), which is involved in the biosynthesis of the aromatic amino acids phenylalanine, tyrosine, and tryptophan (6, 21). It is immobilized by soil and is rapidly degraded by soil organisms (22). Only a few bacteria have been isolated that can utilize phosphonates, which include glyphosate, as their sole source of phosphorus for growth. Two pathways for the breakdown of glyphosate (Fig. 1) have been documented (5, 8, 12, 14, 16, 19). One involves cleavage of the molecule to give aminomethylphosphonate, which is further broken down by subsequent unknown steps. The second pathway is via initial cleavage of the C-P bond to give sarcosine by a C-P lyase activity. Bacteria known to degrade glyphosate via sarcosine include Pseudomonas sp. strain PG2982 (8) and Arthrobacter sp. strain GLP-1 (14). In this paper, Rhizobium meliloti and many other members of the family Rhizobiaceae are shown to possess glyphosate-degrading ability. Our efforts have focused on R. meliloti 1021 (RM1021), since this strain is well characterized both genetically and biochemically. Metabolism of glyphosate by RM1021 was found to follow the sarcosine pathway, implicating C-P lyase activity. MATERIALS AND METHODS Chemicals. N-Phosphonomethylglycine (isopropylamine salt; technical grade, 86%) was provided by Monsanto Co., St. Louis, Mo. Methyl-and ethylphosphonic acids and diethylphosphite were obtained from Alfa Products, Danvers, Mass. Sarcosine, aminomethyl phosphonic acid (AMPn), and vitamins were obtained from Sigma Chemical Co., St. Louis, Mo. Formaldehyde (37%) and glycine were purchased from Aldrich Chemical Co., Milwaukee, Wis.
