Manganese reduction coupled to the oxidation of ammonium and sulphur - a geochemical curiosity or an important biogeochemical process?

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While the contribution of organic matter oxidation to the biogeochemical cycles is well understood, a large number of putative lithotrophic processes has so far been overlooked but are assumingly widespread and important in the environment. Examples for these 'novel' processes are the oxidation of reduced sulphur species or ammonium coupled to manganese reduction, processes driven by the isolates investigated in this study. The manganese-dependent oxidation of ammonium produces nitrogen gas and may be responsible for 90% of the nitrogen loss in marine sediments. Investigating this process is, therefore, not only important for the understanding of the biogeochemical cycles. As nitrogen is removed from the system and not available for primary production, this type of anaerobic ammonium oxidation may play an important role in avoiding eutrophication, particularly in coastal areas. Similarly, manganese-dependent oxidation of sulphur compounds (elemental sulphur, thiosulphate) is a so far unknown process. However, it connects the element cycles of sulphur and oxygen in marine sediments and helps solving a major biogeochemical problem: the transfer of electrons from sulphide to oxygen spatially separated in different sediment layers. As these compounds are present also in subsurface sedments and aquifers they might also provide a basis for life for the 'Deep Biosphere'.