We assessed the presence and quantified the intracellular virus-like particles (VLPs) in natural populations of Aureococcus anophagefferens during the 1999-2000 brown tide blooms that occurred in New Jersey coastal waters. From samples taken during the blooms in both years, 0.2 to 8.1% of individual A. anophagefferens cells contained VLPs and displayed a wide range of ultrastructural changes from apparently healthy cells to those showing late stages of production of VLPs. VLP-infected cells usually had an electron dense plasma membrane and lacked the typical exocellular polysaccharide layer (EPS). The VLPs were similar in size (c. 140 nm) and morphology to those initially, reported in natural populations of A. anophagefferens and to brown tide viruses (BtVs) which were previously isolated and inoculated into laboratory cultures of A. anophagefferens. VLP-infected A. anophagefferens were found consistently throughout the brown tide blooms in both years in Little Egg Harbor. Percentages of VLP-infected cells were 8.1% at the beginning of a bloom, which decreased to less than 2% at the height of the blooms during both years, and increased at the end of the 2000 bloom to 2.5%. While these percentages appear low, the estimated VLP infection rate of A. anaphagefferens cells, which ranged from 0.83%-50% of the standing population, is comparable to other studies.
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