Anaerobic Benzene Oxidation in the Fe(III) Reduction Zone of Petroleum-Contaminated Aquifers

Abstract

The potential for anaerobic benzene oxidation in the Fe(III)reduction zone of petroleum-contaminated aquifers was evaluated. Sediments were incubated under strict anaerobic conditions without any amendments in order to simulate in situ conditions. [ 14 C]Benzene was not oxidized to 14 CO 2 at most sites examined, which is consistent with previous studies that have found that benzene tends to persist in unamended, anaerobic aquifer materials and/or long periods of time are required in order to adapt the microbial population for benzene degradation. However, at one site located in Bemidji, MN, [ 14 C]benzene was oxidized to 14 CO 2 in unamended sediments without an apparent lag, suggesting that benzene was anaerobically degraded in situ. Benzene was not significantly oxidized in sediments from nearby Fe(III)-reducing sites nor in sediments collected from an uncontaminated background site in the same aquifer. Culturing and 16S rRNA-based molecular studies of the Bemidji aquifer demonstrated that while all sites contained similar numbers of Fe(III)-reducing microorganisms closely related to Geothrix fermentens, the site at which anaerobic benzene degradation was observed was greatly enriched with microorganisms in the family Geobacteraceae. This study provides the first data consistent with in situ anaerobic oxidation of benzene to carbon dioxide in the Fe(III)reducing zone of a petroleum-contaminated aquifer and suggests that comparative studies on the size of the Geobacteraceae community in petroleum-contaminated aquifers might aid in the location of zones in which benzene degradation coupled to Fe(III) reduction is taking place.

Subsurface clade of Geobacteraceae that predominates in a diversity of Fe(III)-reducing subsurface environments

“…Fe(III) reduction is an important terminal electron-accepting process in portions of the aquifer (Lovley et al, 1989;Lovley, 1995;Anderson et al, 1998;Rooney-Varga et al, 1999;Holmes et al, 2005;Nevin et al, 2005). Sediments were collected from the Fe(III) reduction zone of the contaminant plume in 2004 with split spoon sample cores and transported immediately to the laboratory as previously described .…”

“…In sediments collected in 2004 from the previously described (Lovley et al, 1989;Lovley, 1995;Anderson et al, 1998;Rooney-Varga et al, 1999;Holmes et al, 2004bHolmes et al, , 2005Nevin et al, 2005) petroleum-contaminated aquifer in which Geobacter Serial dilutions were made in medium containing acetate (10 mM) provided as the electron donor, and poorly crystalline Fe(III)-oxide (100 mM) provided as the electron acceptor. A standard three-tube MPN chart was consulted to estimate cell numbers (95% confidence interval).…”

“…To address these questions, we conducted detailed field experiments for two consecutive summers at the previously described (Anderson et al, 2003;Holmes et al, 2005;Vrionis et al, 2005) uranium-contaminated site located in Rifle, CO. We also investigated two other sites: (1) an acetateimpacted aquifer in Plymouth, MA which serves as an analog for the long-term inputs of acetate that could be expected in subsurface environments during prolonged in situ bioremediation of uranium contamination; and (2) a petroleum-contaminated aquifer in which Geobacter species are considered to play an important role in the oxidation of aromatic hydrocarbon contaminants coupled to Fe(III) reduction (Anderson et al, 1998;RooneyVarga et al, 1999;Holmes et al, 2004b). The results suggest that a phylogenetically coherent subsurface clade of Geobacter species dominates the microbial communities associated with these diverse Fe(III)-reducing subsurface environments, as well as several previously investigated subsurface environments.…”

The use of stable isotope probing to identify key iron-reducing microorganisms involved in anaerobic benzene degradation

“…Benzene has caused the most concern since it is known to be a potential human carcinogen (Dean, 1985) and the factors that control its degradation especially in anaerobic environments are still poorly understood. Aerobic degradation of benzene is well studied and also several reports are available on anaerobic benzene degradation under denitrifying (Burland and Edwards, 1999), sulfate-reducing (Lovley et al, 1995;Phelps and Young, 1999), iron-reducing (Kazumi et al, 1997;Anderson et al, 1998;Jahn et al, 2005) and methanogenic conditions (Weiner and Lovley, 1998).…”

Developments in Bioremediation of Soils and Sediments Polluted with Metals and Radionuclides – 1. Microbial Processes and Mechanisms Affecting Bioremediation of Metal Contamination and Influencing Metal Toxicity and Transport

“…Both Fe(III)-and sulfate-reducing organisms are known to enzymatically reduce contaminant metals such as U(VI), Cr(VI), Co(III) and Tc(VII) in laboratory cultures (Lovley et al 1991;Lovley & Phillips 1992a, b;Gorby & Lovley 1992;Lovley 1993;Caccavo Jr. et al 1994;Gorby & Bolton 1998;Tebo & Obraztsova 1998; but for remediation purposes it is necessary to demonstrate that the appropriate microorganisms are present within the contaminated subsurface. Members of the Geobacteraceae (d-proteobacteria) are of particular note as these organisms have been identified as a dominant group within sediments upon the stimulation of Fe(III)-reducing conditions (Snoeyenbos-West et al 2000;Finneran et al 2002;Holmes et al 2002;Anderson et al 2003) and in contaminated sediment where Fe(III) reduction is a dominant process (Anderson et al 1998;Ro¨ling et al 2001;Cummings et al 2003). Geobacteraceae were also recently detected within the groundwater of an uraniumcontaminated aquifer during a test of stimulated in situ U(VI) reduction (Anderson et al 2003).…”