Anaerobic utilization of toluene by marine alpha- and gammaproteobacteria reducing nitrate

Abstract

Aromatic hydrocarbons are among the main constituents of crude oil and represent a major fraction of biogenic hydrocarbons. Anthropogenic influences as well as biological production lead to exposure and accumulation of these toxic chemicals in the water column and sediment of marine environments. The ability to degrade these compounds in situ has been demonstrated for oxygen-and sulphate-respiring marine micro-organisms. However, if and to what extent nitratereducing bacteria contribute to the degradation of hydrocarbons in the marine environment and if these organisms are similar to their well-studied freshwater counterparts has not been investigated thoroughly. Here we determine the potential of marine prokaryotes from different sediments of the Atlantic Ocean and Mediterranean Sea to couple nitrate reduction to the oxidation of aromatic hydrocarbons. Nitrate-dependent oxidation of toluene as an electron donor in anoxic enrichment cultures was elucidated by analyses of nitrate, nitrite and dinitrogen gas, accompanied by cell proliferation. The metabolically active members of the enriched communities were identified by RT-PCR of their 16S rRNA genes and subsequently quantified by fluorescence in situ hybridization. In all cases, toluene-grown communities were dominated by members of the Gammaproteobacteria, followed in some enrichments by metabolically active alphaproteobacteria as well as members of the Bacteroidetes. From these enrichments, two novel denitrifying toluenedegrading strains belonging to the Gammaproteobacteria were isolated. Two additional toluenedegrading denitrifying strains were isolated from sediments from the Black Sea and the North Sea. These isolates belonged to the Alphaproteobacteria and Gammaproteobacteria. Serial dilutions series with marine sediments indicated that up to 2.2¾10 4 cells cm -3 were able to degrade hydrocarbons with nitrate as the electron acceptor. These results demonstrated the hitherto unrecognized capacity of alpha-and gammaproteobacteria in marine sediments to oxidize toluene using nitrate.

Implications of Limited Thermophilicity of Nitrite Reduction for Control of Sulfide Production in Oil Reservoirs

“…S3 in the supplemental material). Although we did not detect nitrate reduction with xylenes, the use of m-xylene as an electron donor for nitrate reduction with accumulation of nitrite under mesophilic conditions has been reported previously (34,48).…”

Acetate Production from Oil under Sulfate-Reducing Conditions in Bioreactors Injected with Sulfate and Nitrate

“…With nitrate and/or nitrite breakthrough, the proportion of the hNRB Thauera increases considerably (see 2-PW and 7-PW in Table S1). Increases in other potential hNRB, e.g., Pseudomonas (32) and Deferribacteraceae (7), are also seen. The latter were not observed in bioreactors, but Thauera clearly increases in bioreactors when nitrate is included.…”

“…In applying this biotechnology (25)(26)(27)(28), volatile fatty acids (VFA; e.g., acetate, propionate, and butyrate) are often considered to be the predominant electron donors for nitrate reduction and decisions with respect to the nitrate dose to be used take VFA concentrations in produced waters into account (29). Direct use of oil components, especially toluene, as electron donors for nitrate reduction has also been demonstrated (30,31,32). When VFA were used as electron donors in microcosm or bioreactor studies, production of acetate from propionate and butyrate was seen under sulfate-reducing, but not under nitrate-reducing, conditions (33,34).…”

Microbial response to oil enrichment in Gulf of Mexico sediment measured using a novel long-term benthic lander system

“…These groups are not known to be involved in anaerobic hydrocarbon degradation. Most known anaerobic hydrocarbon degraders from marine sediment are either sulfate-reducing bacteria from the Deltaproteobacteria (Rueter et al, 1994;Kniemeyer et al, 2007;Musat et al, 2008) or nitrate reducers from the Alphaproteobacteria, Betaproteobacteria, and Gammaproteobacteria (Heider et al, 1999;Alain et al, 2012). These phylogenetic classes were present in relatively low and unchanging abundance in this study (Figure 9).…”