Date of Award

1986

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Abstract

The pathway for the degradation of glyphosate (N-phosphonomethylglycine) by Pseudomonas sp. PG2982 has been determined using metabolic radiolabeling experiments. Radiorespirometry experiments utilizing 3-('14)C glyphosate revealed that approximately 50-59% of the C3 carbon was oxidized to CO(,2). Fractionation of stationary phase cells labeled with 3-('14)C glyphosate revealed that from 45-47% of the assimilated C3 carbon is distributed to proteins and that the amino acids methionine and serine are highly labeled. The nucleic acid bases adenine and guanine received 90% of the C3 label that was incorporated into nucleic acids, and the only pyrimidine base labeled was thymine. These results indicated that C3 of glyphosate was at some point metabolized to a C1 compound whose ultimate fate could be both oxidation to CO(,2) and distribution to amino acids and nucleic acid bases that receive a C1 group from the C1-donating coenzyme tetrahydrofolate. Pulse labeling of PG2982 cells with 3-('14)C glyphosate revealed that 3-('14)C sarcosine is an intermediate in glyphosate degradation. Examination of crude extracts prepared from PG2982 cells revealed the presence of an enzyme that oxidizes sarcosine to glycine and formaldehyde. These results indicate that the first step in glyphosate degradation by PG2982 is cleavage of the carbon-phosphorus bond, resulting in the release of sarcosine and a phosphate group. The phosphate group is utilized as a source of phosphorus, and the sarcosine is degraded to glycine and formaldehyde. This pathway is supported by the results of 1,2-('14)C glyphosate metabolism studies which showed that radioactivity in the proteins of labeled cells was found only in the glycine and serine residues. Inorganic phosphate inhibits glyphosate metabolism at the transport level but does not seem to have a direct effect on the oxidation of C3 of glyphosate to CO(,2). Phosphonate utilization by Pseudomonas sp. PG2982 was investigated. Each of the ten phosphonates tested were utilized as a sole source of phosphorus by PG2982. Representative compounds tested included alkylphosphonates, 1-amino-substituted alkylphosphonates, amino-terminal phosphonates, and an arylphosphonate. PG2982 cultures degraded phenylphosphonate to benzene and produced methane from methylphosphonate. The data indicate that PG2982 is capable of cleaving the carbon-phosphorus bond of several structurally different phosphonates.

Pages

98

Share

COinS