Bacterial strains isolated from fertilizer industry effluent: characterization and exploration of their efficiency in potentially toxic elements bioremoval

Industrial discharges contain often hazardous components particularly potentially toxic elements (PTEs). Autochthons bacteria isolated from industrial effluents could play a pivotal role on its bio depollution particularly in terms of PTEs. The present investigation was conducted with the objective of isolating, identifying bacterial strains from effluent discharged by the phosphate fertilizer industry (PFI) in southwestern Tunisia, and exploring their potential for PTEs removal. Using various in-vitro procedures and media, we have isolated ten bacterial strains from the effluent. The isolates were identified by 16S rDNA gene sequencing, and their potential attributes for bioremediation were evidenced. In addition to their remarkable acidity and salinity, the effluent contained significant levels of PTEs. Hence, the acidotolearnt and halotolerant isolated bacteria were found to belong to the genera Bacillus, Pseudomonas, Stenotrophomonas and Providencia. Safety consideration features (DNase, hemolysin and antibiotics susceptibility) confirmed collectively the non-pathogenicity of the bacterial isolates. Moreover, the strains exhibited substantial tolerance to PTEs (Cd, Cr, Fe, Mn, Al, Pb and Zn). PTEs removal assays using the newly isolated bacteria, in single and multi-element aqueous media, revealed encouraging results. In single element solutions removal efficiencies were as following Cd (27.76%-65.08%), Fe (5.83%-40.69%), Zn (3.01%-61.41%), Cr (1.57%-76.77%), Mn (19.47%-58.31%), Pb (8.20%-75.45%) and Al (3.53%-25.38%). Overall, removal efficiencies in multi-element system were lower than in single element solutions. Stenotrophomonas maltophilia (S7) exhibited the highest removal potential of PTEs in the multi-element solution. Inoculating pure colonies of each isolate in PFI wastewaters showed substantial capacities of detoxification of all PTEs. Joining good features of multi-stress tolerance and eminent potentialities of PTEs removal, the isolated strains could be used as a strong tool for PTEs bioremediation and mitigating therefore the harmful impacts on the ecosystem.