Studies On Biodegradation Of Herbicide Glyphosate By Stenotrophomonas Maltophilia Gp 1

Abstract

In the present study, biodegradation of glyphosate by specifically isolated bacterial isolates is described. For quantification of glyphosate during its biodegradation, the use of spectrophotometric methods is convenient compared to more sophisticated chromatographic methods such as LC-MS, GC-MS, etc. Hence, a new spectrophotometric method based on formation of dithiocarbamate copper complex of glyphosate was developed with LOD of 28.9 and#956;g/mL, LOQ of 96.4 and#956;g/mL and Beer Lambert Law range up to 500 and#956;g/mL. The above method could quantify glyphosate in culture medium and soil microcosm without interference of AMPA, glycine and soil contaminants. Among 115 bacterial isolates capable of degrading glyphosate which were obtained by enrichment culture technique, three isolates identified using their 16S rRNA sequence i.e. Stenotropomonas maltophilia GP-1, Citrobacter europaeus GP-75, Bacillus wiedmannii GP-105 were selected for evaluation of their glyphosate degradation ability. After 96 h, Stenotropomonas maltophilia GP-1, Citrobacter europaeus GP-75, Bacillus wiedmannii GP-105 utilized glyphosate to an extent of 76.6%, 69.2% and 54.2 %, respectively. S. maltophilia GP-1, grew and completely mineralized high concentrations of glyphosate (up to 1.0 g/L) suggesting that it could be used for bioremediation of glyphosate-contaminated environments. The effect of various factors influencing growth and biodegradation of glyphosate by S. maltophiia GP-1 such as concentration of glyphosate, nutrient supplementation, pH, temperature, aeration, inoculum, etc. were studied using one-factor at a time followed by response surface methodology. Under optimum conditions i.e. glyphosate 1.0 g/L; glucose 1.5 g/L; ammonium sulphate 1.8 g/L, KH2PO4 0.6 g/L and 1% (v/v) inoculum with agitation (150 rpm, 30±1 and#730;C) for 48 h, S. maltophilia GP-1 could utilize 71.0% of glyphosate present initially. Using resting cell assay, when cells of S. maltophilia GP-1 were incubated with glyphosate, release of phosphate through breakdown of C-P bond was obse