Biodegradation of glyphosate by Stenotrophomonas maltophilia GP-1 involves C-P lyase pathway

In bacteria, the biodegradation of glyphosate involves the aminomethylphosphonic acid (AMPA) pathway and the C-P lyase pathway. In the present study, the pathway involved in biodegradation of glyphosate by isolate Stenotrophomonas maltophilia GP-1 was elucidated. Sarcosine and glycine were detected in the cell-free extracts of S. maltophilia GP-1 using thin layer chromatography and LC-MS/MS indicating the role of a glyphosate-specific C-P lyase. However, aminomethylphosphonic acid (AMPA); the key intermediate of glyphosate degradation was found to be absent. The C-P lyase activity (0.4 U) was determined in terms of the release of Pi from glyphosate breakdown. The key genes involved in C-P lyase and AMPA pathway are (i) phnJ and sox, and (ii) goxB (glyphosate oxidoreductase), respectively. Using polymerase chain reaction, amplicons of expected sizes for individual genes encoding for components of C-P lyase were obtained suggesting the presence of phn operon. Subsequently, in the genome sequence of S. maltophilia GP-1, the entire phn operon and sox gene were found to be present. When the expression of key genes of C-P lyase pathway phnJ and sox was studied using qRT-PCR, higher expression of phnJ (tenfold) was observed in the absence of phosphate, while the expression of sox (5.5 fold) remained unaffected. Thus, the presence of phosphate in the environment affects the catabolism of glyphosate through the interplay between phn operon and Pho regulon. The present study, is the first report on the existence of the C-P lyase pathway and the genes encoding the components of the above pathway in a strain of S. maltophilia.