Summary auto-generated
Researchers isolated and characterized Geothrix fermentans strain H-5T, a novel dissimilatory Fe(III)-reducing bacterium from petroleum-contaminated aquifer sediments. This Gram-negative, strictly anaerobic rod is notable for being the first Fe(III)-reducing bacterium belonging to the Holophaga-Acidobacterium phylum. The organism oxidizes simple organic acids (acetate, propionate, lactate) and long-chain fatty acids (palmitate) completely to CO₂ using Fe(III) as the sole electron acceptor. It can also use alternative electron acceptors including Mn(IV), nitrate, and humic acid analogues. Unusually, strain H-5T can grow fermentatively on citrate or fumarate without an electron acceptor present, producing acetate and succinate as end-products. The bacterium contains c-type cytochrome(s) characteristic of Fe(III)-reducing organisms. Phylogenetic analysis based on 16S rRNA sequencing showed it is only distantly related to other known Fe(III) reducers. Field studies indicated this organism and closely related species are numerically significant in Fe(III)-reducing zones of aquifers, potentially as numerous as Geobacter species.
Key findings
- Geothrix fermentans is a novel Fe(III)-reducing bacterium phylogenetically distinct from all previously characterized Fe(III) reducers, belonging to the Holophaga-Acidobacterium phylum.
- The organism can completely oxidize long-chain fatty acids like palmitate and various organic acids to CO₂ using Fe(III) as the sole electron acceptor.
- Strain H-5T can grow fermentatively on citrate or fumarate without an external electron acceptor, producing acetate and succinate as primary end-products.
- Field evidence indicates that organisms closely related to H-5T are numerically significant in petroleum-contaminated aquifers, being as abundant as Geobacter species in some zones.
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Abstract
In an attempt to understand better the micro-organisms involved in anaerobic degradation of aromatic hydrocarbons in the Fe(III)-reducing zone of petroleum-contaminated aquifers, Fe(III)-reducing micro-organisms were isolated from contaminated aquifer material that had been adapted for rapid oxidation of toluene coupled to Fe(III) reduction. One of these organisms, strain H-5(T), was enriched and isolated on acetate/Fe(III) medium. Strain H-5(T) is a Gram-negative strict anaerobe that grows with various simple organic acids such as acetate, propionate, lactate and fumarate as alternative electron donors with Fe(III) as the electron acceptor. In addition, strain H-5(T) also oxidizes long-chain fatty acids such as palmitate with Fe(III) as the sole electron acceptor. Strain H-5(T) can also grow by fermentation of citrate or fumarate in the absence of an alternative electron acceptor. The primary end-products of citrate fermentation are acetate and succinate. In addition to various forms of soluble and insoluble Fe(III), strain H-5(T) grows with nitrate, Mn(IV), fumarate and the humic acid analogue 2,6-anthraquinone disulfonate as alternative electron acceptors. As with other organisms that can oxidize organic compounds completely with the reduction of Fe(III), cell suspensions of strain H-5(T) have absorbance maxima indicative of a c-type cytochrome(s). It is proposed that strain H-5(T) represents a novel genus in the Holophaga-- Acidobacterium phylum and that it should be named Geothrix fermentans sp. nov., gen. nov.