Organosulfur consumption and cycling in marine chemosynthetic symbioses (OSSY)

• Applicant: Dr. Eileen Kröber
• Subject Area: Microbial Ecology and Applied Microbiology ; Metabolism, Biochemistry and Genetics of Microorganisms
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 519818445

The importance of organosulfur (OS) compounds for the biology and ecology of the oceans has only recently become clear. It is now recognized that OS compounds play a key role in biogeochemical cycles, ranging from critical sources of sulfur, carbon and energy for marine microorganisms to affecting the Earth's climate. Despite the realization of their importance, our understanding of how OS compounds are produced, consumed and cycled is still limited. Environments rich in OS compounds such as dimethylsulfoniopropionate (DMSP) and dimethylsulfide (DMS), like coral reef sediments, seagrass meadows, and mangroves, often harbor a wide diversity of chemosynthetic symbioses. In these associations, the chemosynthetic bacteria provide their eukaryotic hosts with nutrition by assimilating inorganic and organic carbon. Remarkably, it is not known if OS compounds can be metabolized by chemosynthetic symbionts. Given that nutrition is often limiting in the environments where chemosynthetic hosts thrive, the ability to use OS compounds would provide a valuable source of energy and carbon to the symbiosis. In this project, I propose to show that OS compounds are important for the nutrition of chemosynthetic symbioses. My analyses of the metagenomes of several groups of chemosynthetic hosts, such as gutless oligochaetes and clams have revealed that their symbionts encode key genes involved in degrading DMSP, DMS, and their intermediates such as methanethiol. Furthermore, these genes are expressed based on transcriptomic analyses of the gutless oligochaete Olavius algarvensis. These preliminary analyses lay the groundwork for an in-depth analysis of OS consumption and cycling in chemosynthetic symbioses. I will combine biogeochemical and molecular biological approaches such as metatranscriptomics, metaproteomics and metabolomics, coupled with incubation experiments using labelled OS compounds, to identify the pathways used by chemosynthetic symbionts to gain energy and carbon from DMSP and DMS. The proposed research will focus on the following questions: 1) How widespread is OS degradation in chemosynthetic symbioses? 2) Which metabolic pathways are fueled by OS degradation, and how is the carbon and sulfur from these compounds cycled within the symbiosis? 3) Are the pathways used by chemosynthetic symbionts for OS degradation and cycling also present in their closely-related free-living relatives? Or were these pathways acquired recently through horizontal gene transfer? 4) What is the environmental relevance of chemosynthetic OS degradation and cycling? Given the extensive expertise I have gained during my PhD and postdoctoral research in the biogeochemistry and molecular biology of microbial OS degradation and cycling, combined with my close collaborations with research groups working on chemosynthetic symbioses, I am well positioned to fill in major gaps of our understanding of how chemosynthetic symbioses contribute to the marine organic sulfur cycle.

• DFG Programme: Independent Junior Research Groups