Abstract
We examined the potential for CH4 oxidation to be coupled with oxygen derived from the dissimilatory reduction of perchlorate, chlorate, or via chlorite (ClO−2) dismutation. Although dissimilatory reduction of ClO−4 and ClO−3 could be inferred from the accumulation of chloride ions either in spent media or in soil slurries prepared from exposed freshwater lake sediment, neither of these oxyanions evoked methane oxidation when added to either anaerobic mixed cultures or soil enriched in methanotrophs. In contrast, ClO−2 amendment elicited such activity. Methane (0.2 kPa) was completely removed within several days from the headspace of cell suspensions of Dechloromonas agitata CKB incubated with either Methylococcus capsulatus Bath or Methylomicrobium album BG8 in the presence of 5 mM ClO−2. We also observed complete removal of 0.2 kPa CH4 in bottles containing soil enriched in methanotrophs when co-incubated with D. agitata CKB and 10 mM ClO−2. However, to be effective these experiments required physical separation of soil from D. agitata CKB to allow for the partitioning of O2 liberated from chlorite dismutation into the shared headspace. Although a link between ClO−2 and CH4 consumption was established in soils and cultures, no upstream connection with either ClO−4 or ClO−3 was discerned. This result suggests that the release of O2 during enzymatic perchlorate reduction was negligible, and that the oxygen produced was unavailable to the aerobic methanotrophs.
Highlights
In-situ production of CO2 by microbial activity is encouraged during enhanced oil recovery as a means of reducing oil viscosity and improving flow characteristics (Lazar et al, 2007; Youseff et al, 2009)
We examined the potential for CH4 oxidation to be coupled with oxygen derived from the dissimilatory dissimilatory reduction of perchlorate, reduction of ClO−4 and cChlOlo−3ratceo, uolrdvibaechinlofreitrere(dClfOro−2m) ditshme uatcactiuomn.uAlaltthioonugohf chloride ions either in spent media or in soil slurries prepared from exposed freshwater lake sediment, neither of these oxyanions evoked methane oxidation when added to either anaerobic mixed cultures or soil enriched in methanotrophs
Little is known about the fate ofchlorate in anoxic environments like oil reservoirs
Summary
In-situ production of CO2 by microbial activity is encouraged during enhanced oil recovery as a means of reducing oil viscosity and improving flow characteristics (Lazar et al, 2007; Youseff et al, 2009). Targeted growth of microbes and intentional precipitation of solid phase minerals can be applied to selectively decrease permeability and direct flow to enhance oil recovery (Jenneman et al, 1984; Zhu et al, 2013) These enhancements rely on the availability of appropriate electron acceptors to supply oxidant to microbes utilizing hydrocarbons or other reduced compounds as electron donors. A similar phenomenon was noted that could link biological oxidation of arsenite to the reduction of chlorate ions, presumably by liberation of O2 (Sun et al., 2010) This type of interaction has not been extended to the oxidation of low molecular weight hydrocarbons such as methane (CH4). In our study we explored the potential for aerobic CH4 oxidizing bacteria to utilize oxygen produced by DPRB during (per)chlorate reduction and chlorite dismutation
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