Work Package 8 (Simon, Dittmar, Blasius)

"Bridging the gap between bacterial species exometabolomics and geometabolomics in pelagic ecosystems"

Broader background of the proposed research project

There is accumulating evidence that marine DOM is an extraordinarily diverse blend of indi-vidual organic compounds and consists of thousands of different molecular formulae (Flerus et al. 2012, Lechtenfeld et al. 2015, Osterholz et al. 2015a). The DOM diversity patterns appear to be very constant over space and time in marine pelagic systems, assuming that sources and sinks act rather similarly. Phytoplankton primary production and microbial DOM processing, are the primary biological sources and sinks but still little is known about the impact of individual phytoplankton algae and heterotrophic bacteria on the composition of marine DOM. It has been shown that the molecular diversity of the exometabolome of a marine pelagic alphaproteobacterium, Pseudovibrio sp., growing in rich organic media is very different from that of marine DOM (Romano et al. 2014) but, when growing at natural DOM concentrations, has a distinct impact on the diversity of marine DOM (Schwedt et al. 2015). Also natural marine bacterial communities clearly influence the diversity and composition of marine DOM (Lechtenfeld et al. 2015, Osterholz et al. 2015a).

Outline for the proposed PhD research project

We hypothesize that the concerted action of individual marine microbes are instrumental in shaping the marine geometabolome. To address the above mentioned hypothesis we will carry out a comprehensive comparative data analysis of the exometabolomes of individual and mixed bacterial species, phytoplankton communities, geometabolomic DOM patterns and the composition und functional properties of bacterioplankton communities. The aim is to elucidate how the marine geometabolome is shaped by the metabolic activity of microbes and to identify the significance and function of individual microbial species and communities for these processes. Data will be provided by ongoing projects on the exometabolome of marine Roseobacter species within TRR 51 Roseobacter and approved research cruises of RV Sonne in the Pacific in 2016 (transect at ~180°E from 30°S to 60°N) and 2017 (transect at ~180°E from 30°S to 60°S) for marine DOM and bacterioplankton community data. Further, if granted, additional data will be provided by large scale mesocosm experiments to investigate phytoplankton blooms under different nutrient stoichiometry which are planned for 2016 and 2017 (PlanktoDyn). If necessary, these data will be complemented by few specific experiments to address distinct questions on the role of individual microbes, bacteria and/or phytoplankton algae, in the context of DOM processing and their role in geometabolomics.