VIRUSES INFECTING THE MARINE PRYMNESIOPHYTE CHRYSOCHROMULINA SPP - ISOLATION, PRELIMINARY CHARACTERIZATION AND NATURAL-ABUNDANCE

Sixty-four natural virus communities were concentrated from seawater collected from 3 locations in Texas (USA) coastal waters (Gulf of Mexico, 27 degrees 31' N, 96 degrees 18' W; Aransas Pass, 27 degrees 50' N, 97 degrees 02' W; Laguna Madre, 27 degrees 30' N, 97 degrees 18' W) and screened for the presence of lytic pathogens which infect the marine Prymnesiophyte (Haptophyte) Chrysochromulina brevifilum. Viruses were detected in 16 of the samples and ranged in abundance from 2 to 688 infectious units l(-1). The pathogens were detected at the 3 locations, but not on all dates, from December through June when water temperatures were less than 28 degrees C. A clonal isolate of the virus (CbV-PW1) was obtained by determining the concentration of the infectious agent by a most-probable-number assay and adding 0.2 of an infective unit into each of 20 exponentially growing cultures, removing an aliquot from a culture which lysed and repeating the procedure. The isolate also caused lysis of C. strobilus, but did not lyse 8 other isolates of Chrysochromulina or 5 other genera of Prymnesiophytes that were screened. The double-stranded DNA virus is a polyhedron of about 145 to 170 nm in diameter with a heavily staining central region that is distinct from the capsid. The appearance of the virions is associated with a granular region in the cytoplasm that does not appear within uninfected cells. Ultimately, viral production results in disruption of the organelles, lysis of the cell and release of the virus particles. Although the number of viruses produced per lytic event is presently unknown we have counted more than 320 virus particles in a single ultrathin section of an infected cell. These results suggest that viruses are likely important in regulating Chrysochromulina populations in the sea and may be the reason that blooms of the genus are relatively rare and ephemeral.