Isolation and characterization of polycyclic aromatic hydrocarbons (PAHs) degrading, pH tolerant, N-fixing and P-solubilizing novel bacteria from manufactured gas plant (MGP) site soils

Dearth of high molecular weight contaminant degradation, pH tolerance and growth limiting nutrient assimilation potentials of the selected microorganisms are some of the prime factors reasonable for the failures in field-scale bioremediation of PAHs contaminated soils. Hence an effort was made in this study for the first time to identify HMW PAHs degrading, N-fixing and P-solubilizing bacteria with pH tolerance from long-term manufactured gas plant site soils. Four distinct strains that could degrade both LMW and HMW PAHs were identified. Among the isolates, Stenotrophomonas (MTS-2) followed by Citrobacter (MTS-3) and Pseudomonas (MTS-1) were furthermost effective in the degradation of HMW PAHs either as individual or in the presence of co-substrate (LMW PAHs). MTS-1, 2 and 3 (co)degraded model LMW PAHs, Phe (100% of 150 mg L^-1) and HMW PAHs Pyr (100% of 150 mg L^-1) or BaP (90-100% of 50 mg L^-1) in 3, 12-15 and 30 days, respectively and recorded the least half-life time (t^1/2) and highest biodegradation rate constants (k). One of the significant findings is the diazotrophic P-solubilization ability, acid and alkali tolerance (optimum pH=5.0-8.0) of the HMW PAHs degrading Pseudomonas strain MTS-1. Stenotrophomonas (MTS-2) was also found to be superior as it could solubilize P and tolerate acidic condition (optimum pH=5.0-7.5) during HMW PAHs degradation. Further, our study is the first evidence of diazotrophic P solubilization potential of Agrobacterium (MTS-4) and P-solubilizing capacity of Citrobacter (MTS-3) during bioremediation. Thus, the results of this study demonstrate the promising use of the newly identified PAH degraders, notably MTS-1, 2 and 3 either as individuals or as consortia as an excellent candidate in the bioremediation or phytoremediation of PAHs contaminated soils.