The silent bacterial majority: understanding the genetic, metabolic and membrane contribution of non-mitochondrial symbioses to the origin of eukaryotes (BACSYMEK)

A project funded by the join Moore and Simons Foundations' initiative 'Deciphering the origin of the eukaryotic cell'. PI, Puri Lopez-Gacia. In collaboration with David Moreira, Laura Eme and Philippe Nghé.

Eukaryogenesis represents a unique evolutionary transition. Elusive for a long time, reconstructing a mechanistically and ecologically plausible model for the origin of eukaryotes now appears feasible thanks to advances in molecular phylogenomics and a better understanding of microbial diversity and interactions in natural ecosystems. In particular, the discovery of Asgard archaea, which share more, and more similar, genes with eukaryotes than other archaea, along with the syntrophic nature of the first cultured Asgard members strongly support cooperative, symbiogenetic models for the origin of the eukaryotic cell, whereby higher complexity evolved from the physical integration of prokaryotic cells and extensive gene and genome shuffling. Most symbiogenetic models invoke only two partners at the origin of the eukaryotic cell, an Asgard-like archaeon and the alphaproteobacterial ancestor of mitochondria. However, non-alphaproteobacterial genes seem to outnumber genes of alphaproteobacterial origin in eukaryotes. Is this silent bacterial majority the consequence of horizontal gene transfer (HGT) from bacteria to the archaeal ancestor of eukaryotes? Do those genes, often encoding cohesive functions, attest to pre-mitochondrial symbioses? Could the host of the eukaryogenetic consortium have been a bacterium and the nucleus derive from an Asgard-like endosymbiont as the Syntrophy Hypothesis posits?

BACSYMEK aims at answering these questions combining data from classical microbiology, microfluidics, metagenomics, single-consortium genomics and phylogenomics.