Synergistic degradation of polycyclic aromatic hydrocarbons by two functional strains in the presence of Tween-80

Abstract:

[Objective] To study the synergistic remediation efficiency of polycyclic aromatic hydrocarbons (PAHs) by mixed functional bacteria constructed by Pseudomonas putida B6-2 and Klebsiella sp. CW-D3T, and explore the effect of non-ionic surfactant Tween-80 on the degradation of PAHs by mixed bacteria, to provide the potentials and insights for the biodegradation of aromatic compounds. [Methods] In this study, we measured the bacteria-growth curve and the determined proportion of mixed bacteria by standard plate count method, thereby exploring the feasibility of mixed bacteria degradation system. We investigated the degradation efficiencies of PAHs by pure cultures and bacterial mixed cultures at different concentrations of Tween-80 using high-performance liquid chromatography. Finally, we conducted the cell surface hydrophobicity assay by an alkane adsorption method to explore the mechanism of Tween-80 in affecting the degradation of PAHs by mixed functional bacteria. [Results] The growth state of the two strains mixed in equal proportion was better than that of the pure culture system. After 7 days, the degradation rates of mixed PAHs (phenanthrene, fluoranthene, and pyrene) were 33.4%, 30.1%, and 28.6%, respectively, which were 1.31 times, 1.46 times and 1.42 times higher than those of strain CW-D3T. The degradation rates of phenanthrene, fluoranthene, and pyrene with the addition of 500 mg/L Tween-80 to the mixed bacterial culture were 47.7%, 43.2%, and 38.8%, respectively, which were 1.55 times, 1.38 times, and 1.31 times higher than those in the control group. However, higher concentrations of Tween-80 did not significantly promote or slightly inhibit the degradation of PAHs. The addition of Tween-80 increased the surface hydrophobicity of strain CW-D3T and mixed bacteria while decreasing that of strain B6-2. Combined with the number of bacterial colonies results, the higher concentration of Tween-80 produced certain toxicity to strain B6-2 and inhibited its growth, thereby affecting the degradation efficiency of mixed bacteria. [Conclusion] The composite functional bacteria constructed by P. putida B6-2 and Klebsiella sp. CW-D3T has a good efficiency in degrading aromatic compounds. A low concentration of Tween-80 can be utilized as a carbon source and change the hydrophobicity of the cell surface, thus significantly improving the removal efficiency of phenanthrene, fluoranthene and pyrene.