Synergistic effects of a functional bacterial consortium on enhancing phenanthrene biodegradation and counteracting rare earth biotoxicity in liquid and slurry systems.

ABSTRACT

The biodegradation of polycyclic aromatic hydrocarbons (PAHs) by micro-organisms in the environment is often inhibited by coexisting metal ions. The aim of this work is to study a bacterial consortium for enhancing phenanthrene biodegradation under the inhibition effect of the rare earth (RE) ions Ce3+ and Y3+ . This bacterial consortium was composed of two bacteria, namely, the RE-adsorbing Bacillus subtilis MSP117 and the phenanthrene-degrading Moraxella osloensis CFP312. Ce3+ and Y3+ at the concentration of 1·15 mmol l-1 inhibited CFP312 from degrading phenanthrene but not glucose. Using glucose as a co-substrate could promote the proliferation of CFP312 but decreased phenanthrene degradation. Adsorption experiments and electron microscopy imaging showed that CFP312 had no RE ions adsorption capacity for RE ions and that RE elements could not be observed on its cell surfaces. MSP117 could adsorb 0·14 and 0·12 mmol g-1 wet cells of Ce3+ and Y3+ in aqueous solution, respectively, thus demonstrating considerable adsorption capacity. The MSP117 cell surface immobilized part of the free RE ions and reduced their bioaccessibility, thereby alleviating their biotoxic effect on phenanthrene degradation by CFP312. In liquid and slurry systems, glucose, which was used as the co-substrate of the bacterial consortium, must be kept at a low level to avoid the catabolism repression of phenanthrene degradation by CFP312.