Successional changes in an evolving anaerobic chlorophenol-degrading community used to infer relationships between population structure and system-level processes

The response of a complex methanogenic sediment community to 2-chlorophenol (2-CP) was evaluated by monitoring the concentrations of this model contam inant and important metabolic intermediates and products and by using rRNA- targeted probes to track several microbial populations. Key relationships b etween the evolving population structure, formation of metabolic intermedia tes, and contaminant mineralization were identified. The nature of these re lationships was intrinsically linked to the metabolism of benzoate, an inte rmediate that transiently accumulated during the mineralization of 2-CP. Be fore the onset of benzoate fermentation, reductive dehalogenation of 2-CP c ompeted with methanogenesis for endogenous reducing equivalents. This suppr essed H-2 levels, methane production, and archaeal small-subunit (SSU)-rRNA concentrations in the sediment community. The concentrations of bacterial SSU rRNA, including SSU rRNA derived from "Desulfovibrionaceae" populations , tracked with 2-CP levels, presumably reflecting changes in the activity o f dehalogenating organisms. After the onset of benzoate fermentation, the a bundance of Syntrophus-like SSU rRNA increased, presumably because these sy ntrophic organisms fermented benzoate to methanogenic substrates. Consequen tly, although the parent substrate 2-CP served as an electron acceptor, cle avage of its aromatic nucleus also influenced the sediment community by rel easing the electron donors H, and acetate. Increased methane production and archaeal SSU-rRNA levels, which tracked with the Syntrophus-like SSU-rRNA concentrations, revealed that methanogenic populations in particular benefi ted from the input of reducing equivalents derived from 2-CP.