Previously unknown ssDNA molecules co‐occurring with CdebDNAV infecting the marine planktonic diatom Chaetoceros debilis

Abstract

SUMMARYSince the first discovery of diatom viruses, more than a dozen species have been identified, and these viruses can significantly affect the dynamics of diatoms in nature. To better understand marine primary productivity, details of the relationship between viruses and their diatom hosts must be elucidated. The marine diatom Chaetoceros debilis is a cosmopolitan species and its blooms are often observed in highly productive areas. To date, only C. debilis DNA virus (CdebDNAV) has been isolated and characterized. In this study, we successfully identified a previously unknown virus‐like particle (VLP) and ssDNA molecules co‐occurring with CdebDNAV. Transmission electron microscopy analysis of the cytoplasm of infected C. debilis revealed particles that were 21 and 36 nm in size, corresponding to the newly identified VLPs and CdebDNAV, respectively. The ssDNA molecules encode a putative capsid protein (CP); however, no proteins related to replication were detected. The estimated molecular weight of the CP is 24.4 kDa, similar to that of VLPs in the protein electrophoresis analysis. Genetic analyses revealed that the CP shows low levels of similarity with uncultured marine ssDNA viruses, but seems to be independent of the known virus genera. Although the relationships between the smaller VLP and ssDNA molecules identified in this study were not fully revealed, it might be a new virus. The finding is important for understanding diatom virus ecology and to promote further characterization of uncultured aquatic ssDNA viruses.