Biodegradation of selected homocyclic aromatic compounds and carbon tetrachloride under iron(III) reducing conditions

Possible treatments of selected non-oxygenated, homocyclic aromatic hydrocarbons (e.g., benzene, toluene, ethylbenzene, and o-xylene) and compounds with oxygenated substituents (e.g., cresols, phenol, and benzoic acid) as well as (bio)transformation of carbon tetrachloride were evaluated under Fe(III)-reducing conditions. Fe(III)-reducing cultures enriched from sediments at a former manufactured gas plant (MGP) site (Baltimore, Maryland) used toluene, ethylbenzene, and o-xylene, and p-cresol as sole carbon and energy sources with initial concentrations of 30 μM to 130 μM. In the presence of 100 mM amorphous Fe(OH)₃(s), the cell growth doubling times (T_d) ranged from 27 to 47 days. The addition of 1 mM NTA (nitrilotriacetic acid, a Fe(III) chelating agent) to the Fe(III)-reducing enrichment cultures enhanced biodegradation of toluene in the presence of 100 mM amorphous Fe(OH)₃(s).; The toluene-degrading, Fe(III)-reducing enrichment cultures were capable of using amorphous Fe(OH)₃(s) as the terminal electron acceptor coupled to p-cresol transformation. p-Hydroxybenzaldehyde, p-hydroxybenzoic acid, and benzoic acid were detected as metabolic intermediates during p-cresol transformation. Addition of acetate, lactate, fumarate and succinate as co-substrates significantly stimulated benzene degradation in several sediment samples from the former MGP site under strictly anaerobic conditions (Fe(III)-reducing conditions).; The Fe(III)-reducing bacterium, Geobacter metallireducens, was capable of using acetate as carbon and energy source coupled to reduction of selected quinonoid-type compounds such as anthraquinone-2,6-disulfonate (AQDS), anthraquinone-2-sulfonate (AQS) and 1,8-dihydroxy-9,10-anthraquinone (AQDH). In the presence of benzoic acid, phenol, and p-cresol as carbon and energy sources, Geobacter metallireducens was capable of degrading benzoic acid, phenol, and p-cresol coupled to the reduction of AQDS and AQS. The addition of 1 mM AQDS to the Geobacter metallireducens cultures stimulated the transformation of p-cresol and Fe(III) reduction in the presence of amorphous Fe(OH)₃(s). Both biologically and chemically reduced AQDS could reduce Fe(III) to Fe(II).; Carbon tetrachloride was transformed to chloroform in the presence of different electron donors, Fe(III) forms, and electron transfer mediators (e.g., riboflavin, lawsone, and AQDS) under Fe(III)-reducing conditions. Chloroform was detected as a transformation product in all experiments. Microbial-mediated and Fe(II, III)-mineral-surface-mediated reactions may catalyze the transformation of carbon tetrachloride under Fe(III)-reducing conditions.; Dissimilatory iron(III) reducing bacteria (DIRB) with versatile metabolic characteristics not only are capable of degrading (or transforming) organic (e.g., petroleum pollutants and chlorinated solvents), but also create reactive Fe(II, III) surfaces that may catalyze transformation of chlorinated solvents. Enhancement of biodegradation of petroleum pollutants may be achieved by addition of humic substances as electron transfer mediators under Fe(III)-reducing conditions.