Daphnia Iridovirus 1 Genome Assembly. Daphnia Iridovirus 1

The planktonic freshwater crustacean Daphnia magna is a model system for the ecology and evolution of host-parasite interactions, but so far no virus has been characterized for this system. White fat cell disease (WFCD) has been studied in Daphnia for over 60 years without its causative agent being described. This disease is highly virulent for its host and has been reported from several sites in Eurasia. Iridovirus infections have been observed with symptoms similar to those of WFCD in natural Daphnia populations. Here we report that an iridovirus is the causative agent of WFCD. We report the genome sequence of this iridovirus, named Daphnia iridescent virus 1 (DIV-1). It has a length of ~288 kbp, a G+C content of 38.8% and encodes 367 predicted open reading frames. The DIV-1 genome seems to have experienced both substantial gene loss and gain of a high number of unique genes, probably acquired through horizontal gene transfer (HGT). These genes may play a role in adaptations of the virus to its crustacean host. DIV-1 represents the first invertebrate iridovirus encoding proteins with putative functions for RNA capping, and contains unique genes for an immunoglobulin-like protein, a membrane glycoprotein, and a DnaJ-like protein, which may mediate host-pathogen interactions and pathogenicity. DIV-1 clusters together with other invertebrate iridoviruses, but has by far the largest genome among all sequenced iridoviruses. Our findings end a 60-year search for the causative agent of WFCD and adds substantially to our knowledge of iridovirus genomics.