Characterization of microbial consortia that reductively dechlorinate 4-chlorophenol and transform phenol to benzoate enriched from estuarine sediment of Lake Shinji

Magnetite drives self-dechlorination of 4-chlorophenol in anoxic aquatic sediments

The lack of available electron donors is well known as a major factor limiting the efficiency of microbial dechlorination of 4-chlorophenol (4-CP) in anoxic aquatic sediments. Considering that Fe(III) minerals largely contained in sediments can especially enrich Fe(III)-reducing bacteria and unlock the ring-like intermediates produced by dechlorination of 4-CP via dissimilatory Fe(III) reduction, a strategy of self-dechlorination of 4-CP utilizing its metabolism intermediates such as short-fatty acids (SCFAs) as the endogenous electron donors with magnetite was proposed in this study. The results showed that the removal efficiency of 4-CP increased by 156-203% in magnetite-supplemented biotic groups compared with the magnetite-free biotic group. Liquid chromatography-mass spectrometer (LC-MS) and gas chromatography (GC) revealed the possible metabolic pathway of anoxic 4-CP degradation with magnetite: 4-CP→phenol→cyclohexene-1-carboxylic acid→2-hydroxycyclohexanecarboxylic acid→hexanoic acid/valeric acid→butyric/propionic acids→CO₂. High-throughput sequencing analysis showed that the abundance of functional bacteria, Desulfuromonas, Pseudomonas and Bacillus species, were increased by 1.38-1.97, 1.50-2.04, and 11.60-17.18 folds in magnetite-supplemented biotic groups, compared with the magnetite-free biotic groups. Analysis of Fe²⁺ concentration and cyclic voltammetry (CV) suggested that the potential Fe(III)/Fe(II) transformation occurred and proceeded the anoxic 4-CP degradation continuously.

Anaerobic 4-chlorophenol mineralization in an enriched culture under iron-reducing conditions

We enriched an anaerobic, soil-free 4-chlorophenol (4-CP)-degrading culture under iron-reducing conditions. The [ring-(14)C(U)]4-CP tracer experiment showed that 65 μM 4-CP mineralized to CO2 and CH4 through phenol, 4-hydroxybenzoate, and benzoate intermediates over 60 days. 16S rRNA gene analyses suggested the involvement of Dehalobacterium in the 4-CP dechlorination in the culture.

Bacterial degradation of chlorophenols and their derivatives

Chlorophenols (CPs) and their derivatives are persistent environmental pollutants which are used in the manufacture of dyes, drugs, pesticides and other industrial products. CPs, which include monochlorophenols, polychlorophenols, chloronitrophenols, chloroaminophenols and chloromethylphenols, are highly toxic to living beings due to their carcinogenic, mutagenic and cytotoxic properties. Several physico-chemical and biological methods have been used for removal of CPs from the environment. Bacterial degradation has been considered a cost-effective and eco-friendly method of removing CPs from the environment. Several bacteria that use CPs as their sole carbon and energy sources have been isolated and characterized. Additionally, the metabolic pathways for degradation of CPs have been studied in bacteria and the genes and enzymes involved in the degradation of various CPs have been identified and characterized. This review describes the biochemical and genetic basis of the degradation of CPs and their derivatives.