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Marine microbes block greenhouse gas entering atmosphere

Scientists have developed two novel bioreactors for studying the anaerobic oxidation of methane (AOM) in marine environments in order to learn more about the role of microorganisms in limiting this greenhouse gas.
Marine microbes block greenhouse gas entering atmosphere
Methane (CH4) is a powerful greenhouse gas, but the amount emitted to the environment from ecosystems is limited by some types of microorganisms. These microorganisms, known as methanotrophs, oxidise CH4 to obtain energy and a carbon source for their metabolism. Although methane oxidation can occur aerobically or anaerobically little is known about anaerobic methanotrophs.

The anaerobic oxidation of methane by microbes known as archaea coupled to the reduction of sulphate (SO42-) by bacteria prevents CH4 from being emitted to the atmosphere from the marine environment. The microorganisms responsible for this process and their pathways were investigated by the SUREANMETOX (Sulphate reduction dependent anaerobic methane oxidation in novel membrane and electrochemical bioreactors) project.

Researchers developed two distinct reactors for the enrichment of microorganisms conducting AOM. In one reactor an external membrane was used to enable the efficient retention of biomass, while the other reactor was designed as a trickling packed bed to ensure retention. Sulphate reduction was measured together with sulphide production in both the membrane bioreactor (MBR) and the packed bed reactor (PBR).

Sediment from the Ginsburg mud volcano in the Gulf of Cadiz was used as an anaerobic inoculum for the MBR reactor. Illumina high-throughput sequence analysis of 16SrRNA genes showed that even after operating the reactor for about 360 days levels of anaerobic methanotroph (ANME) archaea were low. Similar results were found for the PBR.

Because of the logistical difficulties involved in the retrieval of deep marine sediments with high AOM activity researchers also explored the use of sediments taken from Lake Grevelingen. This is a marine lake in the Netherlands that was formerly part of the Rhine Meuse estuary.

High rates of deposition and the degradation of organic matter have resulted in methane rich anoxic sediments, which combined with sulphate from seawater means the lake is a potential niche for AOM. Evidence of AOM was found at depths of 5 to 15cms in the sediment. ANME and archaeal cells were detected by 16rRNA gene sequencing and observed using fluorescence in situ hybridization (FISH) analysis.

SUREANMETOX revealed for the first time evidence for the occurrence of AON in sediments from Lake Grevelingen. In addition, the MBR and PBR reactors enabled project partners to obtain enrichment cultures which will help to isolate key players in the global CH4 cycle.

Related information


Anaerobic oxidation, methane, methanotrophs, archaea, sulphate, bacteria, SUREANMETOX, membrane bioreactor, packed bed reactor, 16SrRNA, Lake Grevelingen, fluorescence in situ hybridization
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