Do Viruses Exchange Genes across Superkingdoms of Life?

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

To test, we divided eukaryoviruses into five subgroups representing viruses of fungi, plants, metazoa, protozoa, and invertebrates-plants (viruses that can replicate in both plants and insect vectors), as defined by the NCBI Viral Genomes Resource (Figure 4) . FSF distributions of the five subgroups of eukaryoviruses were mapped to the seven Venn groups already defined for eukaryoviruses (Figure 2) . The majority of eukaryoviruses belonged to metazoa (n = 1,057) and plant hosts (963) revealing strong biases in the sequencing of human infection, livestock and agriculture related viruses. Interestingly, only 27 viruses were associated to protozoa. These viruses encoded a total of 291 FSFs (the second largest amongst the five eukaryoviral subgroups after 306 FSFs of metazoan viruses). This is expected since protozoa act as natural hosts of many "giant viruses" (e.g., Acanthamoeba polyphaga), which surpass parasitic cellular species both in particle and genome sizes and sometimes encode more than a thousand proteins (La Scola also Table S5 ). P-values were calculated from two-sample Welch t-tests. Arslan et al., 2011; Philippe et al., 2013; Legendre et al., 2015) . However, out of the total 65 BE FSFs detected in eukaryoviruses (Figure 2) , 40 (62%) were detected in metazoan viruses and 32 (49%) in protozoan viruses (overlap of 14 common FSFs) (Figure 4) . Animals are known hosts for symbiotic bacteria and also harbor large microbiota communities, especially in the gastrointestinal tract that is considered to be a "melting pot" for HGT (Shterzer and Mizrahi, 2015) . Similarly, freeliving amoeba (e.g., Acanthamoeba) are notorious reservoirs for both facultative and obligate intracellular bacteria and serve as "training grounds" to facilitate bacterial adaptation in eukaryotic cells (Barker and Brown, 1994; Molmeret et al., 2005) . These two eukaryotic host subgroups therefore provide ample opportunities for eukaryoviruses to exchange genetic material either directly with bacterial proteomes or through prophages integrated in bacterial genomes.