Strain diversity of giant viruses infecting chlorarachniophyte algae in the subtropical Pacific

The chlorarachniophyte alga Bigelowiella natans has been suggested as a potential host for giant viruses, but no isolates could thus far confirm this observation. Here, we present four closely related strains of giant viruses that infect B. natans and related algae, and therefore we designate them as chlorarachniophyte viruses (ChlorVs).

We characterize their infection cycle and show that ChlorVs possess a large host range among chlorarachniophytes. The genomes of all strains were assembled using a combination of long and short reads, revealing linear topologies with terminal inverted repeats and sizes between 469 and 493 kbp. Phylogenetic analysis of marker genes using complex evolutionary models places the ChlorVs in the same subfamily as the Cafeteria roenbergensis virus (CroV) and the Chlorella virus XW01, indicating that switches between distantly related hosts are more common than previously known.