We have been working to characterize viruses that infect the HAB-forming pelagophyte Aureococcus anophagefferens Hargraves et Sieburth. Field samples were collected during brown-tide events in 2002 and tested for the presence of lytic agents. Here, we describe a recently isolated, lytic virus-like particle (VLP) that is morphologically similar to particles observed in thin sections of infected A. anophagefferens cells from natural samples. TEM and SEM have revealed VLPs consistent with the morphological characteristics of previously described Phycodnaviridae. Large icosahedral particles (similar to 140 nm) of similar shape and morphology dominate cell lysates and are accompanied by smaller phage-like particles and heterotrophic prokaryotes that appear to be incurable from our cultures. To determine which of these particles interacts with the Aureococcus cells, we preserved cultures during the early stage of infection so that SEM could be used to visualize those particles that attach to the surface of naive cultures. SEM revealed that 63% of the large icosahedral-shaped particles attached to A. anophagefferens cells after only 30 min of exposure, while no significant frequency of attachment to the alga was observed for the phage-like particles. The results of these observations are in contrast to previous studies, where phage-like particles were reported to infect cells. When considered in conjunction with field observations, the results suggest that this newly isolated virus represents the dominant virus-morphotype associated with bloom collapse and termination.
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