A distinct lineage of giant viruses brings a rhodopsin photosystem to unicellular marine predators

Needham DM, Yoshizawa S, Hosaka T, Poirier C, Choi CJ, Hehenberger E, Irwin NAT, Wilken S,Yung CM, Bachy C et al. – PNAS

Although viruses are well-characterized regulators of eukaryotic algae, little is known about those infecting unicellular predators in oceans. We report the largest marine virus genome yet discovered, found in a wild predatory choanoflagellate sorted away from other Pacific microbes and pursued using integration of cultivation-independent and laboratory methods. The giant virus encodes nearly 900 proteins, many unlike known proteins, others related to cellular metabolism and organic matter degradation, and 3 type-1 rhodopsins. The viral rhodopsin that is most abundant in ocean metagenomes, and also present in an algal virus, pumps protons when illuminated, akin to cellular rhodopsins that generate a proton-motive force. Giant viruses likely provision multiple host species with photoheterotrophic capacities, including predatory unicellular relatives of animals.

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