Kinetic study of the biodegradation of glyphosate by indigenous soil bacterial isolates in presence of humic acid, Fe(III) and Cu(II) ions

Abstract

The present study was executed to investigate the kinetics of the biodegradation of glyphosate in an aqueous medium. Three bacterial strains (Streptomyces sp., Bacillus subtilis, and Rhizobium leguminosarum) with excellent glyphosate-degrading capabilities were isolated from the agricultural soils and characterized on the basis of 16S ribosomal RNA (rRNA) gene sequencing methods. Biodegradation of glyphosate was performed with and without applications of metal ions [Fe(III) and Cu(II)] and humic acid (HA). In thirty days experiment, three strains were utilized 85-90% (with half life periods from 8.36 to 9.12 days) of glyphosate. Applications of Fe(III) and Cu(II) have inhibited the biodegradation to 70-80% (with half life periods from 10.03 to 11.15 days). In the presence of HA, biodegradation was inhibited significantly (57-70%) with half life periods from 12.54 to 13.09 days. Overall, glyphosate’s biodegradation inhibition order under different conditions was as HA > Cu(II) > Fe (III). UV-visible and mass spectrometric results indicated two concurrent pathways of degradation of glyphosate with major metabolites included glycine, aminomethylphosphonic acid (AMPA), sarcosine, glyoxylate, metaphosphoric acid and phosphate. Glyphosate breakdown by these three strains was achieved by the C-P lyase and the glyphosate oxidoreductase activity. Hence, these strains could be used as potential biological agents in the effective biodegradation campaign for other pesticide-contaminated sites.