Viruses occur in astronomic numbers everywhere on Earth, from the atmosphere to the deepest ocean. Surprisingly, considering the abundance and nutrient-richness of viruses, no organisms are known to use them as food. On September 24, 2020, in Frontiers in Microbiology (https://www.frontiersin.org/articles/10.3389/fmicb.2020.524828/full), researchers published the first compelling evidence that two groups of ecologically important marine protists, choanozoans (image) and picozoans, are virus eaters, catching their "prey" through phagocytosis (i.e., engulfing). The open-access article is titled “Single Cell Genomics Reveals Viruses Consumed by Marine Protists.” "Our data show that many protist cells contain DNA of a wide variety of non-infectious viruses but not bacteria, strong evidence that they are feeding on viruses rather than on bacteria. That came as a big surprise, as these findings go against the currently predominant views of the role of viruses and protists in the marine food webs," says corresponding author Ramunas Stepanauskas, PhD, Director of the Single Cell Genomics Center at Bigelow Laboratory for Ocean Sciences in East Boothbay, Maine, USA. Dr. Stepanauskas and colleagues sampled surface seawater from two sites: the Northwestern Atlantic in the Gulf of Maine, USA, in July 2009, and the Mediterranean off Catalonia, Spain, in January and July 2016. They used modern single-cell genomics tools to sequence the total DNA from 1,698 individual protists in the water. Each of the resulting “single amplified genomes” (SAGs) consists of the genome of a single protist, with or without associated DNA: for example, from symbionts, ingested prey, or viruses or bacteria sticking to its exterior.
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