Temporal distributions of functional microbes and putative genes associated with halogenated phenol anaerobic dehalogenation and further mineralization

Abstract

Several anaerobic systems have been established for mineralizing halogenated aromatics (HACs) by construction of dehalogenation and oxidative degradation consortia. However, functional interplay of bacterial and genetic activity during HAC mineralization is poorly understood. In this study, the temporal distributions of potential dehalogenators, oxidative degraders and relevant functional genes were investigated in an anaerobic consortium for mineralizing HACs. The consortium held wide mineralization potential, and was able to mineralize various types of HACs with halogens in the ortho- and meta-positions, such as 4-chlorophenol (4-CP) and 2,4,6-trichlorophenol (2,4,6-TCP). Copy numbers of the potential dehalogenators (Dehalobacterium and Sulfurospirillum spp.) and phenol degraders (Geobacter spp.) proliferated enormously (10–10² copies per ml) and remained at a high level (10⁵ to 10⁷ copies per ml) throughout the 4-CP and 2,4,6-TCP mineralization processes (60 days). Meanwhile, the growth of two functional genes, putative chlorophenol reductive dehalogenase cprA and benzoyl-CoA reductase bamB genes showed similar trends, with numbers increased by over 10 copies per ml on average. In comparison, without the addition of HAC, no significant growth of potential dehalogenators, degraders and functional genes was observed. The distribution trends of functional bacteria and genes revealed simultaneous satisfaction of the redox niches of both dehalogenation and oxidative degradation by the enriched consortium. This study proposed the complete mineralization of a wide range of HACs by supplying one consortium containing multiple functional microbes and a simple nutrient supplement under anaerobic conditions.