Distribution, community assembly and metabolic potential of sulfate-reducing microorganisms in marine sediments

Publikation: Bog/antologi/afhandling/rapportPh.d.-afhandlingForskning

    Lara Jochum
The marine sulfur and carbon cycles are coupled closely together by the activity of sulfate reducing microorganisms (SRM) in marine subsurface sediments. Here, they are responsible for oxidizing up to 50 % of the organic carbon contained in marine sediments. Marine sediments are characterized by decreasing availability of organic matter and sulfate with sediment depth. SRM are a taxonomically and metabolically diverse group and populate both surface and subsurface marine sediments. Large subgroups of environmental SRM are uncultured, particularly in marine subsurface sediments, and their physiology and strategy for subsisting under sulfate and organic carbon limitation in marine sediments is poorly understood.
In this thesis I have studied the distribution, community assembly and metabolic potential of SRM populating in the coastal marine sediments of Aarhus Bay. Firstly, I investigated how SRM communities in marine sediment change across the vertical depth profile of sediment cores by next generation sequencing of a functional marker gene indicative of SRM. The abundance, distribution and identity of SRM at different depths were assessed and the results compared with geochemical data. Thereby, I could identify that the SRM community structure and size is most heavily influenced by bioturbation and the associated changes in the availability of organic carbon. Sulfate concentrations had less if any impact on the SRM community structure and therefore it was concluded that marine SRM can thrive under high and low sulfate concentrations.
Further, I used single cell genome sequencing of cells extracted from Aarhus Bay sediments to assess the metabolic potential of deltaproteobacterial populations related to the sulfate reducer Desulfatiglans anilini. These deltaproteobacteria are abundant in subsurface marine sediments and I aimed to understand the metabolic strategies that enable their survival in the subsurface seabed. The results support the theory that a versatile metabolism is important for subsurface microorganisms to be able to adapt to increasingly energy limited conditions the deeper they are buried in the sediment. Notably, however, one group of Desulfatiglans-related bacteria did not show any genetic indication for sulfate reduction, despite this group being generally considered as SRM until now.
The presented results highlight the factors that determine which groups of SRM become predominant in marine sediments, thus providing clues for physiological properties of interest for further studies of marine subsurface SRM. They further emphasize the metabolic diversity that characterizes SRM and likely enables them to thrive across a wide range of environmental conditions.
StatusUdgivet - 28 okt. 2017

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