Membrane changes during syntrophic growth of an archaeal/bacterial consortium: a model for eukaryogenesis

The first eukaryotic cell is assumed to have arisen from a symbiosis of an archaeal cell, likely an Asgard archaeon, and a bacterial partner. As an early stage of eukaryogenesis a syntrophic interaction between the partners has been suggested. Yet, little is known about the role of cell-to-cell contacts for the emergence of eukaryotes. Due to the lack of cultivated and genetically tractable Asgard archaea or closely relevant lineages, model systems of syntrophic interacting microorganisms can help to shed light on how cell-to-cell interactions between different species arose. Here, we specifically focus on determining which membrane lipids and proteins are involved in cell-to-cell interactions. To this end, we use syntrophic cocultures of the sulfate-reducing bacterium Desulfovibrio vulgaris and the methanogenic archaeon Methanococcus maripaludis. In addition to an ancestor coculture, evolved cocultures after 300 & 1000 generations [1] were being analyzed by transcriptomics and proteomics to identify differentially expressed proteins connected to cell-to-cell interactions with a focus on membrane proteins. These analyses are further complemented with lipid analyses to determine changes in the cell membrane of the syntrophic coculture partners as a response to changes in the membrane proteins. To visualize cell interactions fluorescence microscopy was used. The combination of methods revealed membrane changes based on lipids and proteins between mono cultures and syntrophically grown cultures. Furthermore, comparing different coculture generations showed how the cell membrane of both species adapt to syntrophic growth. The observed differences indicate that membrane changes might have already occurred in early stages of eukaryogenesis. In summary, the in-depth analysis of a model syntrophic co-culture will provide clues on how interdomain cell-to-cell interactions lead to the emergence of the first eukaryotic cell and which role early archaea had in it.

[1] Turkarslan et al., (2021) The ISME Journal 15(8):2233-2247.