Commensalism in theMimiviridaegiant virus family

Abstract

22Acanthamoeba-infecting Mimiviridae belong to three clades: Mimiviruses (A), Moumouviruses (B) 23and Megaviruses (C). The uniquely complex mobilome of these giant viruses includes virophages and 24 linear 7 kb-DNA molecules called "transpovirons". We recently isolated a virophage (Zamilon vitis) 25 and two transpovirons (ma B tv and mv C tv) respectively associated to B-clade and C-clade mimiviruses. 26We used the capacity of the Zamilon virophage to replicate both on B-clade and C-clade host viruses 27 to investigate the three partite interaction network governing the propagation of transpovirons. We 28 found that the virophage could transfer both types of transpovirons to B-clade and C-clade host 29 viruses provided they were devoid of a resident transpoviron (permissive effect). If not, only the 30 resident transpoviron was replicated and propagated within the virophage progeny (dominance 31 effect). Although B-and C-clade viruses devoid of transpoviron could replicate both ma B tv and mv C tv, 32 they did it with a lower efficiency across clades, suggesting an ongoing process of adaptive co-33 evolution. We performed proteomic comparisons of host viruses and virophage particles carrying or 34 cleared of transpovirons in search of proteins involved in this adaptation process. These experiments 35 revealed that transpoviron-encoded proteins are synthetized during the combined 36 mimiviruses/virophage/transpoviron replication process and some of them are specifically 37 incorporated into the virophage and giant virus particles together with the cognate transpoviron 38 DNA. This study also highlights a unique example of intricate commensalism in the viral world, where 39 the transpoviron uses the virophage to propagate from one host virus to another and where the 40 Zamilon virophage and the transpoviron depend on their host giant virus to replicate, this without 41 affecting the giant virus infectious cycle, at least in laboratory conditions. 42 43 3 Author Summary 44 The Mimiviridae are giant viruses with dsDNA genome up to 1.5 Mb. They build huge viral factories in 45 the host cytoplasm in which the nuclear-like virus-encoded functions (transcription and replication) 46 take place. They are themselves the target of infections by 20 kb-dsDNA virophages, replicating in 47 the giant virus factories. They can also be found associated with 7kb-DNA episomes, dubbed 48 transpovirons. We investigated the relationship between these three players by combining 49 competition experiments involving the newly isolated Zamilon vitis virophage as a vehicle for 50 transpovirons of different origins with proteomics analyses of virophage and giant virus particles. Our 51 results suggest that relationship of the virophage, the transpoviron, and their host giant virus, extend 52 the concept of commensalism to the viral world. 53 54 55

The Astounding World of Glycans from Giant Viruses

“…51 They can also be found associated with transpovirons, which are 7 kb linear episomes. 51,86 With regard to glyco-related genes, all of the members of this genus encode for several GTs and other enzymes involved in sugar metabolism, as discussed in section 3.1.2.5. 87…”