Large double-stranded DNA viruses which cause the lysis of a marine heterotrophic nanoflagellate (Bodo sp) occur in natural marine viral communities

A virus (BV-PW1) which causes lysis of 2 strains of a marine heterotrophic nanoflagellate belonging to the genus Bodo (strains E1 and E4) was isolated from the coastal waters of Texas, USA. Transmission electron microscopy of ultrathin sections of infected nanoflagellates revealed the presence of intracellular virus-like particles 48 h following infection, concomitant with a decline in flagellate numbers. The virus contains double-stranded DNA, is hexagonal in cross section, ca 230 to 300 nm in diameter and contains an electron dense core. It is morphologically similar to virus-like particles which have been observed in other heterotrophic nanoflagellates, and to viruses which have been isolated which infect eukaryotic phytoplankton. Addition of the virus to cultures of Pseudobodo parvulus (ATCC 50091, formerly Bodo parvulus) or Paraphysomonas imperforata (strain VS1) did not result in lysis. To our knowledge this is the first virus infecting heterotrophic nanoflagellates which has been isolated and maintained in culture. The presence of viruses in seawater which cause lysis of phagotrophic nanoflagellates implies that viruses infect microzooplankton populations in the sea and suggests another important role for viruses in aquatic microbial communities.