Ultrastructural analysis of viral infection in the brown-tide alga, Aureococcus anophagefferens (Pelagophyceae)

Abstract

The DNA-containing virus (BtV) is known to lyse laboratory cultures of Aureococcus anophagefferens Hargraves et Sieburth, an alga known to cause blooms devastating to shellfish and eelgrass beds. Ultrastructural study of the infection of A. anophagefferens by this virus shows a progressive degradation of host algal cells. Healthy uninfected algal cells (c. 2.0 μm) exhibit organelles typical of the Pelagophyceae and are surrounded by a prominent fibrous glycocalyx. All laboratory cultures of A. anophagefferens inoculated with the BtV virus were lysed within 24–48 h, leaving no living cells. Infected brown-tide cells had an unusually electron-dense, crenated plasma membrane and lacked a glycocalyx. During early stages of infection, the vacuole disappeared, and the nucleus was disrupted by the formation of viroplasm. The organelles disappeared, with the chloroplast being the last to degrade. A few intracellular viral capsids (c. 140–160 nm) were observed during the degeneration of the organelles. In the final stages of infection, the entire host cell was filled with viroplasm and viral capsids, and no organelles remained.