Work Package 3
Tracking microbially-mediated biogeochemical processes in oxygen-deficient waters and sediments by metatranscriptomics
Important biogeochemical transformations within the sulfur and nitrogen cycles take place in anoxic or suboxic bottom waters of the BUS, particularly where these meet with oxygen or nitrate containing water from mixing or lateral advection. Here, different groups of prokaryotes contribute to nitrogen loss processes (e.g., anammox), oxygen consumption, and, in the case of sulfidic conditions, to sulfide oxidation (Lavik et al. 2009). The distribution and spatio-temporal variability of these processes, as well as the microbial response towards fluctuating conditions is currently not known. Metagenomic and transcriptomic approaches now allow to assess the metabolic network of the involved microorganisms and to track their responses to changing environmental factors. They can also detect processes that are otherwise overlooked due to fast element cycling as in the case of the cryptic sulfur cycle (Canfield et al. 2010). Further, expressed functional genes are indicators for the localization of specific processes and could be used to improve and validate biogeochemical models of oxygen-deficient marine systems (Louca et al. 2016).
General Questions and Research topics:
- Which microbially-mediated biogeochemical processes occur in water columns and sediments characterized by different degrees of oxygen deficiency?
- Which are the responsible key organisms for the different processes?
- How do the microbial communities change and adapt to shifts in physico-chemical factors?
Samples for metatranscriptomics as well as for microbial abundance and diversity (based on 16S rRNA genes) will be collected by a special in situ fixation system (Feike et al. 2012) at locations for which the physico-chemical settings have been described in detail, and from experiments in which oxygen and sulfide concentrations will be changed. The results will allow to locate specific biogeochemical transformation zones in relation to oxygen concentration and assess the microbial potential to react towards changes in abiotic parameters such as a sudden increase in sulfide concentration.