Visualization of RNA virus infection in a marine protist with a universal biomarker

Abstract

Abstract Half of the marine virosphere is hypothesized to be RNA viruses (kingdom Orthornavirae) that infect abundant micro-eukaryotic hosts (e.g. protists). To test this, quantitative approaches that broadly track infections in situ are needed. Here, we describe a technique – dsRNA-Immunofluorescence (dsRIF) – that uses monoclonal antibodies to assess host infection status based on the presence of double-stranded RNA (dsRNA), a replicative intermediate of all Orthornavirae infections. We show that the dinoflagellate Heterocapsa circularisquama produces dsRIF signal ~1000 times above background autofluorescence when infected by the +ssRNA virus HcRNAV. dsRNA positive virocells were detected across >50% of the 48-hour infection cycle and represented up to 63% of the population. Photosynthetic and chromosomal integrity remained intact during peak replication, indicating HcRNAV avoids interrupting these processes. This work validates the use of dsRIF on marine RNA viruses and their hosts, setting the stage for quantitative environmental applications that will accelerate understanding of virus-driven ecosystem impacts.