“Quasigenus” amongPhycodnaviridae: A diversity of chlorophyte-infecting viruses in response to a dense algal culture in a high-rate algal pond

Abstract

This study approaches a high rate algal pond (HRAP) culture by metagenomic sequencing of the viral DNA fraction, this includes the so-called giant virus fraction (phylumNucleocytoviricota), with the goal of revealing viruses coexisting within an intensified algal culture. A wealth of interesting novel viruses is revealed, including members ofNucleocytoviricota,Lavidaviridae, and polinton-like viruses, which are taxa containing previously characterized algal viruses. Our sequencing results are coupled with a virus targeted qPCR study and 18S rDNA metabarcoding to elucidate potential virus-host interactions. Several species of green algae are identified (Chlorophyta), likely representing the alternating dominant populations during the year of study. Finally, we observe a bloom of viral diversity within the familyPhycodnaviridae(Nucleocytoviricota), including highly related but non-identical genotypes, appearing in the HRAP in September and October 2018. This bloom is most likely the cause of a mass mortality event of the cultured algae that occurred during these same months. We hypothesize that these relatedPhycodnaviridaelineages selectively infect different strains of the same algal species of the GenusPicochlorumthat have been identified in the HRAP by metabarcoding and coined this phenomenon a "quasigenus" by analogy to the RNA virus quasispecies concept.

Time of day of infection shapes development of a eukaryotic algal-Nucleocytoviricotavirocell

“…). In terms of evolution, we relate this to the so-called “quasigenus” effect, where giant viruses diversify into a closely related group capable of different infection strategies to match different strains of a bloom species ( e.g., A. anophagefferens ) and environmental (including light) conditions (Highfield et al, 2014, 2017; Chase et al, 2022a). Seemingly, the mixotrophic capabilities of A. anophagefferens should help the host persist in a bloom state during light-limitation, with the consequence of reducing viral production.…”

“…At this point we note this is a study of just one virus-host system alone, and that in situ other K. quantuckense-related viruses may exhibit different energetics (e.g., physiology, burst sizes, viral particle production in relation to light, etc.). In terms of evolution, we relate this to the so-called "quasigenus" effect, where giant viruses diversify into a closely related group capable of different infection strategies to match different strains of a bloom species (e.g., A. anophagefferens) and environmental (including light) conditions (Highfield et al, 2014(Highfield et al, , 2017Chase et al, 2022a). Seemingly, the mixotrophic capabilities of A. anophagefferens should help the host persist in a bloom state during light-limitation, with the consequence of reducing viral production.…”