Microbial aspects of anaerobic sulphate reduction with methane as electron donor


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Title Microbial aspects of anaerobic sulphate reduction with methane as electron donor
Period 06 / 2004 - 11 / 2009
Status Completed
Dissertation Yes
Research number OND1309775


Atmospheric methane (CH4) is the second most important greenhouse gas. Only CO2 as an anthropogenic source has a stronger greenhouse effect. The main sources for methane production in ocean sediments are thermogenic methane formation and microbial methane formation in past and present. Also methane hydrates at the seafloor are releasing methane to the seawater and consequently to the atmosphere.
Sulphate reduction is an anaerobic microbial process in which sulphate is converted to sulphide. Recent research has indicated that sulphate reduction can be coupled with methane oxidation. In order to reduce sulphate an electron donor is needed. Common electron donors are hydrogen and a variety of organic compounds, like organic acids and alcohols, and methane. Sulphate reducing bacteria (SRB) are well studied and are able to reduce sulphate under anaerobic and micro-aerobic conditions. Also a large amount of substrates and electron donors can be used for growth and sulphate reduction. In vitro oxidation of methane by SRB has not been found, but first clear evidence for anaerobic oxidation of methane (AOM) came from geochemical in situ studies of marine sediments.
No microorganism capable of anaerobic growth on methane as the sole carbon source has yet been cultivated. Fluorescent in situ hybridisation combined with secondary ion mass spectrometry analyses, has provided direct evidence for the involvement of at least two distinct archaeal groups (ANME-1 and ANME-2) in AOM at methane seeps. Although both archaeal groups often occurred in direct physical association with bacteria, they also were observed as monospecific aggregations and as single cells. The driving force for research on this process is that microbial communities intercept and consume methane from anoxic environments, which would otherwise enter the atmosphere. The amount of methane consumed by anaerobic methane oxidation each year is approximately equivalent to 5 to 20% of the total annual methane flux to the atmosphere. Anaerobic methane oxidation is biogeochemically important because methane is a potent greenhouse gas in the atmosphere and is abundant in anoxic environments. Geochemical evidence for this process has been observed in numerous marine sediments along the continental margins, in methane seeps and vents, around methane hydrate deposits, and in anoxic waters.
Current reseach focussus on the microbial aspects of different deep sea sediments and sludge from bioreactors. These samples are screened for anaerobic oxidizing capabilities and can possibly be used in methane fed bioreactors in the future.
Microbial analysis are done with FISH and DGGE and standard microbial techniques.
[Future Research]:
Future research will focus on the microbial behaviour in a membrane or gas-lift bioreactor. The microbial community will be monitored with FISH and DGGE so the change in time can be followed. Chemical analysis on sulphide production, sulphate reduction and methane oxidation will be performed and with the use of 13C-labeled methane. The formation of 13C-CO2 can be measured. (Formation of 13C-CO2 is a positive identification for the occurence of AMO)

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D22100 Microbiology

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