Microbial Communities Associated with Anaerobic Benzene Degradation in a Petroleum-Contaminated Aquifer

Abstract

Microbial community composition associated with benzene oxidation under in situ Fe(III)-reducing conditions in a petroleum-contaminated aquifer located in Bemidji, Minn., was investigated. Community structure associated with benzene degradation was compared to sediment communities that did not anaerobically oxidize benzene which were obtained from two adjacent Fe(III)-reducing sites and from methanogenic and uncontaminated zones. Denaturing gradient gel electrophoresis of 16S rDNA sequences amplified with bacterial orGeobacteraceae-specific primers indicated significant differences in the composition of the microbial communities at the different sites. Most notable was a selective enrichment of microorganisms in the Geobacter cluster seen in the benzene-degrading sediments. This finding was in accordance with phospholipid fatty acid analysis and most-probable-number–PCR enumeration, which indicated that members of the familyGeobacteraceae were more numerous in these sediments. A benzene-oxidizing Fe(III)-reducing enrichment culture was established from benzene-degrading sediments and contained an organism closely related to the uncultivated Geobacter spp. This genus contains the only known organisms that can oxidize aromatic compounds with the reduction of Fe(III). Sequences closely related to the Fe(III) reducer Geothrix fermentans and the aerobe Variovorax paradoxus were also amplified from the benzene-degrading enrichment and were present in the benzene-degrading sediments. However, neither G. fermentans nor V. paradoxusis known to oxidize aromatic compounds with the reduction of Fe(III), and there was no apparent enrichment of these organisms in the benzene-degrading sediments. These results suggest thatGeobacter spp. play an important role in the anaerobic oxidation of benzene in the Bemidji aquifer and that molecular community analysis may be a powerful tool for predicting a site’s capacity for anaerobic benzene degradation.

Identification of enzymes involved in anaerobic benzene degradation by a strictly anaerobic iron‐reducing enrichment culture

“…For aerobic degradation of benzene well studied pathways are known (Gibson et al, 1968). Furthermore, enrichment cultures and microcosm studies indicated that benzene can be effectively degraded in the absence of molecular oxygen under iron-reducing (Lovley et al, 1996;Anderson et al, 1998;Rooney-Varga et al, 1999;Kunapuli et al, 2008), sulfate-reducing (Lovley et al, 1995;Kazumi et al, 1997;Phelps et al, 1998;Caldwell and Suflita, 2000;Abu Laban et al, 2009), denitrifying (Burland and Edwards, 1999;Coates et al, 2001;Ulrich and Edwards, 2003) and methanogenic (Ulrich and Edwards, 2003;Chang et al, 2005) conditions. So far, only two anaerobic benzene-degrading strains were isolated to purity, which were described as denitrifying members of the genera Dechloromonas and Azoarcus (Coates et al, 2001;Kasai et al, 2006).…”

Fluorescent properties of c‐type cytochromes reveal their potential role as an extracytoplasmic electron sink in Geobacter sulfurreducens

“…Molecular analyses of microbial communities have indicated that Geobacter species are the predominant metal-reducing microorganisms in various subsurface sediments in which dissimilatory metal reduction is an important process (Rooney-Varga et al, 1999;Holmes et al, 2002;Anderson et al, 2003;Roling et al, 2003;North et al, 2004;Vrionis et al, 2005). One of the hallmark features of Geobacter species is their abundant c-type cytochromes.…”

Anaerobic degradation of benzene by a marine sulfate‐reducing enrichment culture, and cell hybridization of the dominant phylotype

“…Still, benzene in anoxic surroundings is apparently less readily degraded than its alkylated derivatives; anaerobic degradation of the latter, in particular of toluene, has thus been studied more frequently and in much more detail (Heider, 2007). Anaerobic degradation of benzene was demonstrated under conditions of nitrate reduction (Burland and Edwards, 1999;Ulrich et al, 2005), iron(III) reduction (Anderson et al, 1998;Rooney-Varga et al, 1999), sulfate reduction (Lovley et al, 1995;Phelps et al, 1996;Kazumi et al, 1997;Caldwell and Suflita, 2000) or methanogenesis (Grbić-Galić and Vogel, 1987;Ulrich and Edwards, 2003), either in situ, in laboratory microcosms or in enrichment cultures. Only few pure cultures were reported to utilize benzene anaerobically.…”