Do Viruses Exchange Genes across Superkingdoms of Life?

Malik, Shahana S.; Azem-e-Zahra, Syeda; Kim, Kyung Mo; Caetano-Anollés, Gustavo; Nasir, Arshan

A total of 66 ABE FSFs were detected in the proteomes of archaeoviruses, bacterioviruses, and eukaryoviruses (Venn group abe), again enriched in cell-like functions (highlighted in Table S6 ). The abe "universal" or "core" group of FSFs therefore included FSFs detected in the proteomes of all virus groups (archaeoviruses, bacterioviruses, and eukaryoviruses) and the three superkingdoms (Archaea, Bacteria, and Eukarya). While significant cross-superkingdom indirect genetic exchange cannot be ruled out, the possibility of the same HGT event occurring three times independently and in different ecological habitats should be considered unlikely. The origin of abe FSFs is therefore better and more parsimoniously reconciled with an origin of modern viral lineages in ancient cells that existed prior to the diversification of cellular life and experienced high levels of genome reduction (Nasir et al., 2012a; Claverie and Abergel, 2016) . One interesting observation was the existence of only 2 FSFs belonging to the ae group. An origin of Eukarya from within Archaea has recently been postulated following the reconstruction of the genomes of the candidate archaeal phylum "Lokiarchaeota" and "Asgard" archaea (Zaremba-Niedzwiedzka et al., 2017), which harbor several eukaryote-specific proteins (Guy et al., 2014; Spang et al., 2015 , see Nasir et al., 2016 Da Cunha et al., 2017 for opposite views) . Under this scenario, one should expect stronger affiliation of eukaryoviruses with archaeoviruses, which however does not materialize in the FSF data. also Table S6 ).