Large virus-like particles from vacuoles of phaeodarian radiolarians and from other marine samples

Abstract

Large icosahedral virus-like particles (LVLPs) ranging in dameter from ca 300 to 750 nm occurred in food or waste vacuoles of phaeodarian radiolarians collected in the Paciflc Ocean, the Sargasso Sea and the Weddell Sea. The samples were from coastal to open-ocean waters, surface waters to 2000 m depth, and a variety of seasons. A few LVLPs were also found in bulk sediment trap material, in zooplankton guts and fecal pellets, and in minipellets. Phaeodarians are unique among small marine organisms because they carry a record of their past feeding activity within their phaeodium, a collection of food and waste vacuoles. This probably explains why they often contain abundant LVLPs. Phaeodarians appeared to have acquired the LVLPs while feeding on sinking or suspended particulate material. Calculations based on serial sections indicate that a single phaeodarian could contain thousands of LVLPs. Although their hosts have not been determined, LVLPs are clearly ubiquitous. These particles are being called LVLPs because of similarities in morphology with viruses, but they could be as yet unidentified microorganisms, a type of spore, or possibly an organelle of a eukaryote.