Physiological and functional diversity of phenol degraders isolated from phenol-grown aerobic granules: Phenol degradation kinetics and trichloroethylene co-metabolic activities

Abstract

Aerobic granule is a novel form of microbial aggregate capable of degrading toxic and recalcitrant substances. Aerobic granules have been formed on phenol as the growth substrate, and used to co-metabolically degrade trichloroethylene (TCE), a synthetic solvent not supporting aerobic microbial growth. Granule formation process, rate limiting factors and the comprehensive toxic effects of phenol and TCE had been systematically studied. To further explore their potential at the level of microbial population and functions, phenol degraders were isolated and purified from mature granules in this study. Phenol and TCE degradation kinetics of 15 strains were determined, together with their TCE transformation capacities and other physiological characteristics. Isolation in the presence of phenol and TCE exerted stress on microbial populations, but the procedure was able to preserve their diversity. Wide variation was found with the isolates’ kinetic behaviors, with the parameters often spanning 3 orders of magnitude. Haldane kinetics described phenol degradation well, and the isolates exhibited actual maximum phenol-dependent oxygen utilization rates of 9–449 mg DO g DW−1 h−1, in phenol concentration range of 4.8–406 mg L−1. Both Michaelis–Menten and Haldane types were observed for TCE transformation, with the actual maximum rate of 1.04–21.1 mg TCE g DW−1 h−1 occurring between TCE concentrations of 0.42–4.90 mg L−1. The TCE transformation capacities and growth yields on phenol ranged from 20–115 mg TCE g DW−1 and 0.46–1.22 g DW g phenol−1, respectively, resulting in TCE transformation yields of 10–70 mg TCE g phenol−1. Contact angles of the isolates were between 34° and 82°, suggesting both hydrophobic and hydrophilic cell surface. The diversity in the isolates is a great advantage, as it enables granules to be versatile and adaptive under different operational conditions.