Characterization of anaerobic methane-oxidizing consortia

Within the last decade we have become aware that the sulfate-dependent anaerobic oxidation of methane (AOM) in marine sediments, which had been a geochemical enigma for nearly 30 years, is catalyzed by an inter-domain syntrophic partnership of anaerobic methanotrophic archaea (ANME) and sulfate-reducing bacteria (SRB). These microbial consortia live in sediment zones in which both sulfate and methane are readily available and, most importantly, have been observed to make up the bulk of biomass in sediments above ice-like reservoirs of methane, so-called methane hydrates. Very recently, microbes involved in the AOM with electron acceptors other than sulfate have been discovered, but data on the biology and environmental distribution of these organisms is still very limited. Despite their importance in biogeochemical cycling, the molecular biology of microbial consortia involved in the AOM is far from being understood. Calculations of the underlying energy-yielding reaction suggest that they barely can make a living of the AOM, which is consistent with in situ observations that imply generation times of many months. Yet, these organisms are responsible for the consumption of most of the methane produced below the world`s oceans seafloor and are of considerable importance for the global climate. In this project, ANME/SRB- consortia living from the AOM with either iron, manganese, nitrate and, most importantly, sulfate as electron acceptor will be analyzed using lab mesocosms. By the combination of community-wide metaproteomics and nanometer-scale secondary ion mass spectrometry (NanoSIMS) crucial proteins of these peculiar microbes will be identified and localized on the single-cell to subcellular level. In addition, enzymes which in former studies have been related to these consortia will be examined as well as expression-patterns of selected proteins under different environmental stresses be studied. Information gained in this study will be put into context to each other and the data acquired via the concomitant chemical and geochemical analysis of the mesocosms. By this yet unparalleled combination of high-end techniques we try to bridge the two extremes of the microbiological scale, the ecosystem and the single cell. We expect to gain fundamental new insights into the functional organization of these uncultured microbes and their influence on biogeochemical cycling from the microscopic to global level. Furthermore, the proposed project has the potential to shed new light onto the general principles governing syntrophic partnerships in nature.