Do Viruses Exchange Genes across Superkingdoms of Life?

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

Virus-host affiliations however are largely established by observing the cytopathic effects of viral infection or by microscopy detection of virion particles. These properties relate to the lytic mode of viral reproduction that has historically remained on focus due to the noxious effects that lysis has on human health, livestock, and agriculture. However, viruses can also frequently endogenize by integration into cellular genomes (Feschotte and Gilbert, 2012) , sometimes providing useful novel genes to make them evolutionarily competitive (Cornelis et al., 2012) . Moreover, many viruses either infect bacterial symbionts of eukaryotic cells (e.g., the bacterial component of the human microbiota, Turnbaugh et al., 2007) or reside as prophages in the genomes of obligate intracellular bacteria that infect a wide range of eukaryotic hosts . These virus-cell interactions are largely non-lytic in nature and because they do not yield the classic phenotypic effects of viral infection, have likely remained underestimated through established methods of virus discovery (reviewed in . Importantly, such interactions blur the traditional concept of "virus host" and raise the possibility of viruses interacting (not necessarily in a lytic manner) and exchanging genetic material simultaneously with more than one superkingdom of life. Bordenstein and Bordenstein (2016) recently reported an example of a eukaryotic gene module in bacteriophage WO residing as prophage in the intracellular α-proteobacterium Wolbachia, which infects a large group of insects. In order to produce viral progeny, the bacteriophage WO must neutralize antiviral defense and enter/exit the membranes of both bacterial and eukaryal organisms (Bordenstein and Bordenstein, 2016) . The study therefore offered unique insights into virus-cell interactions that extend beyond their known hosts and identified viruses of endosymbiotic bacteria as interesting examples of vectors with genetic material from non-host superkingdoms.