Characterization of a lytic virus infectious to the bloom-forming microalga Aureococcus anophagefferens (Pelagophyceae)

Aureococcus anophagefferens Hargraves and Sieburth has caused recurring monospecific blooms in Long Island embayments since it was first described in 1985. It was termed the 'brown tide,' due to the resulting water color, and has had a devastating effect on Long Island's (New York) marine ecosystem. In 1992, a virus that was capable of causing lysis of A. anophagefferens was isolated and maintained in culture. We report on the further characterization of this virus, Aureococcus anophagefferens virus-1 (AaV-1), indicated by a buoyant density of 1.2776 g·mL^-1 in a CsCl equilibrium gradient. Electron microscopy revealed a phage with a hexagonal head and tail similar to previously described phages. By using adenovirus for calibration, the virus was found to have a head 50-55 nm wide and a tail 70-75 nm long. The viral band was infectious to A. anophagefferens after dialysis. The virus was composed of at least 16 distinct polypeptides ranging in molecular weight from 20 to 230 kDa. The adsorption coefficient for the virus was 7.2 x 10^-9 mL·min^-1, and the burst size was calculated to be 9.4 viruses per A. anophagefferens cell at 20°C. Complete lysis of A. anophagefferens occurred with a titer as low as 893 viruses·mL^-1, and the lower limit of infectivity was 93 viruses·mL^-1. The virus lost its infectivity between 30°and 40°C. These results suggest that AaV-1 is highly infectious and that the role of the virus in preventing or ending A. anophagefferens blooms needs further investigation.