Microbial degradation of glyphosate and its metabolite AMPA in mineral medium and soil

Glyphosate is a non-selective herbicide and pose significant threat to humans and the environment. In the present study, glyphosate degradation abilities of four microbial cultures (Bacillus amyloliquefaciens, Bacillus subtilis, Pseudomonas fluorescens, and Bacillus piscis) were assessed in mineral salt medium. Glyphosate degradation followed first-order degradation kinetics with half-life of 18.6, 28.9, and 15.9 days in B. amyloliquefaciens, B. subtilis, and B. piscis inoculated media, respectively. Degradation of glyphosate in P. fluorescens inoculated media was found negligible. Bacterial culture of B. piscis, identified by partial sequencing of 16S rRNA gene, exhibited the highest potential for glyphosate degradation in mineral salt medium. Glyphosate degradation using B. piscis was further studied in non-sterile and sterile sandy loam soil at 20 and 50 μg g^-1 fortification levels. It degraded at a faster rate in non-sterile soil than in sterile soil, confirming predominant microbial degradation of glyphosate in soil. Enhanced degradation was not observed by inoculation with B. piscis in soil, however enrichment culture obtained from B. piscis inoculated non sterile soil showed faster degradation in mineral salt medium than that of non-inoculated-non-sterile medium, which confirms that predominant degradation of glyphosate was due to native soil microbes.