A multilevel approach to address the role of Archaeal Symbionts in the Evolution of Life

ongoing

Microbial symbioses play an essential role in most aspects of life’s evolution and enabled major evolutionary events such as the origin of eukaryotes. But in spite of the importance of symbioses, our knowledge is based on a limited number of microbial host-symbiont systems, few of which include Archaea. Notably, recent cultivation-independent approaches have revealed two hugely diverse microbial groups of putative deep-branching archaeal and bacterial symbionts referred to as DPANN and CPR, respectively. 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. This will be achieved using a unique three-pronged strategy that will integrate knowledge from both micro- and macroevolutionary levels: I will place the diverse DPANN in a rooted tree of life including CPR, reconcile the history of their genome content evolution and identify novel host-symbiont systems using sophisticated phylogenomic approaches combined with microscopy. Further, I will elucidate fundamental principles of their genome evolution and interactions, for the first time using experimental evolution approaches to study two cultivated DPANN symbionts in co-culture with their hosts. Finally, I will determine the dynamics of natural populations of known and newly identified archaeal host-symbiont systems and the influence of symbionts on host population structure and genome evolution using a unique approach combining single-cell, metagenomics and population genomics. Altogether, this will allow to provide key insights into the global impact of these symbionts in the deep origins and diversification of cellular life on Earth. Thereby, ASymbEL paves the way for a deeper understanding of symbiotic evolutionary theory and the fundamental laws of cellular evolution.