Potential role of Pseudomonas fluorescens c50 and Sphingobium yanoikuyae HAU in enhancing bioremediation of persistent herbicide atrazine and its toxic metabolites from contaminated soil

This research aimed to decipher the potential utility of Pseudomonas fluorescens strain c50 and Sphingobium yanoikuyae strain HAU in biodegradation and the mechanism of biochemical events occurring during the metabolic route of the herbicide atrazine. The bacterial strains c50 and HAU were isolated and identified based on 16S rRNA gene sequence analysis as P. fluorescens (accession no. OM838401) and S. yanoikuyae (accession no. OM830303), respectively. Both strains could survive in a concentration as high as 200 µg/mL of AT. Desethyl atrazine (DEA), desisopropyl atrazine (DIA), and desethylhydroxy atrazine (DEHA) were three critical metabolites produced during catabolism and quantified using GC–MS/MS. In culture medium, both strains effectively removed AT and its metabolites within 30 d with half-lives ranging from 2 to 9.9 d. Strain c50 performed better than HAU in rapid removal of AT and metabolites. In natural soil without microbial treatment, AT, DEA, DIA and DEHA persisted for 120, 90, 60 and 90 d, respectively with half-lives ranging from 12.1 to 26 d. Application of c50 and HAU accelerated degradation in soil. Persistence time of AT, DEA, DIA and DEHA was reduced to 25–30 d with half-lives ranging from 2.8 to 5.1 d. Strain HAU performed marginal better during biodegradation in soil. Performance of both the strains together was found at par. First-order dissipation kinetics was observed during biodegradation. Increase in microbial biomass carbon from 230 to 670 mg/kg soil indicated about initial surge (150 times) in bacterial population in treated soil and rapid biodegradation of contaminants using later as a food source. This study further revealed that identification of almost all major metabolites and intermediate products is possible using GC–MS/MS. However, reliable quantification of only DEA, DIA, and DEHA is possible without derivatization. Both bacteria could provide eco-friendly alternatives for attenuation of these toxicants from the contaminated soils.