Microbial symbioses play an essential role in most aspects of life’s evolution. Yet, despite the importance of symbioses, our knowledge is based on a limited number of microbial host-symbiont systems, few of which include Archaea. Considering that Archaea comprise a primary domain of life next to the much better studied Bacteria, and that Archaea engaging in symbiotic interactions are hypothesized to have played a major role in the evolution of complex eukaryotic cells, this represents a severe lack in our understanding of the deep history of cellular life and our own origins.
Notably, recent cultivation-independent approaches have revealed two very diverse microbial groups of archaeal and bacterial symbionts referred to as DPANN and CPR, respectively. These symbionts have small genomes and cell sizes and seem to be obligately dependent on partner organisms for growth and survival. However, the hosts of most of these symbionts are unknown and their effect on host populations in the environment has not been addressed so far. Furthermore, the placement of these lineages in the tree of life is unclear: for example, initial work suggests that they may diverge early from the tree of life raising questions as to whether these organisms could help us to better understand the nature of cellular life in the deep past.
The major aims of ASymbEL are to test the hypotheses that (a) DPANN, together with CPR, have key positions in the tree of life, requiring to revise our view on the early evolution of cells and (b) that the diverse DPANN substantially shape the evolution of life through symbiont-host interactions. To this end, we integrate knowledge from both micro- and macroevolutionary levels and use both computational and experimental approaches. Together, this will shed light on the mysterious DPANN archaeal symbionts and their role in life’s biodiversification.
