Marine sediments: interaction partners of cable bacteria revealed through metagenomics

Cable bacteria from the family Desulfobulbaceae are multicellular filamentous electroactive bacteria found worldwide in aquatic sediments. They are capable of coupling sulfide oxidation and oxygen or nitrate reduction by transferring electrons over centimeter-long distances. It was hypothesized that other microorganisms might exploit this feature to access otherwise unreachable environments via direct interspecies electron transfer. In this thesis, a screening for extracellular electron transfer proteins was performed on high-quality genomic bins obtained through the integration of four binning tools. This screening led to a shortlist of ten taxonomic groups which have the potential to conduct electron exchange with cable bacteria, thrive in their presence, or compete with them. The Sulfurimonas genus was the most interesting group. There is evidence that this group may use cable bacteria to indirectly access oxygen in shortage in marine sediments. Simultaneously, Sulfurimonas contain proteins for iron reduction and oxidation, suggesting a potential for electron exchange with cable bacteria. To test this hypothesis, fluorescence in situ hybridization experiment was set up, where two signals were found co-localized with filaments of cable bacteria. Along with previous studies and the presence of electron transfer proteins, this indicates the involvement of Sulfurimonas in electron exchange with cable bacteria.