Viruses are the most abundant biological entities throughout marine and terrestrial ecosystems. They interact with all life forms, including archaea, bacteria and eukaryotic organisms and are present in natural or agricultural ecosystems, essentially wherever life forms can be found (Roossinck, 2010). The concept of a virus challenges the way we define life, especially since the recent discoveries of viruses that possess ribosomal genes. These discoveries include the surprisingly large viruses of the Mimiviridae (Claverie and Abergel, 2012; Yutin et al., 2013), the Pandoraviruses that lack phylogenetic affinity with any known virus families (Philippe et al., 2013) and Pithovirus sibericum that was recovered from Siberian permafrost after being entombed for more than 30,000 years (Legendre et al., 2014). Apparently they co-occurred and even predated cellular forms on our planet, yet arguably they have no certain place in our current view of the tree of life (Brüssow, 2009; Koonin and Dolja, 2013; Thiel et al., 2013). Besides their potential role in evolution, viruses have facilitated the understanding of various basic concepts and phenomena in biology (Pumplin and Voinnet, 2013; Scholthof, 2014). However, they have also long been considered as disease-causing entities and are regarded as major causes of considerable losses in food crop production. Pathogenic viruses imperil food security by decimating crop harvests as well as reducing the quality of produce, thereby lowering profitability.
