New Isolates of Betachloroviruses Shed Light on the Diversity and Biological Complexity of an Unexplored Group of Giant Algal Viruses

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Abstract
The majority of giant algal viruses belong to the family Phycodnaviridae, class Algavirales, phylum Nucleocytoviricota. Among them, the genus Chlorovirus is the most studied, with three recognized groups based on genomics and host range, although many fundamental questions remain to be elucidated, particularly regarding their diversity. In this study, we focus on betachloroviruses, a poorly explored subgroup that infects the alga Micractinium conductrix Pbi. Here, we describe the isolation and genomic analysis of 11 new betachloroviruses from water samples collected in Nebraska, USA. With 25 fully sequenced genomes now available, we assessed the genomic diversity of these viruses. They have double-stranded DNA genomes ranging from 295 to 374 kbp, encoding hundreds of ORFs, of which a large number (~40%) lack known function. Comparative genomics and phylogenetic analyses revealed three species of betachlorovirus, each with high intra-species genomic identity. Notably, some isolates with over 99.5% genomic identity display markedly different plaque phenotypes, which led us to propose the use of the term genomovar among giant algal viruses, a concept potentially applicable to other giant viral groups yet to be explored. Altogether, this work advances our understanding of betachloroviruses and highlights the importance of linking viral genotype to phenotype, opening new avenues for exploring the diversity of giant algal viruses.
Funding Information
  • Conselho Nacional de Desenvolvimento Científico e Tecnológico (402038/2023-1, APQ-01057–23, Finance Code 001, 1736030)
  • Fundação de Amparo à Pesquisa do Estado de Minas Gerais (402038/2023-1, APQ-01057–23, Finance Code 001, 1736030)
  • Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (402038/2023-1, APQ-01057–23, Finance Code 001, 1736030)
  • National Science Foundation (402038/2023-1, APQ-01057–23, Finance Code 001, 1736030)
  • University of Nebraska-Lincoln Agricultural Research Division (402038/2023-1, APQ-01057–23, Finance Code 001, 1736030)
  • University of Nebraska-Lincoln Office of Research and Economic Development (402038/2023-1, APQ-01057–23, Finance Code 001, 1736030)
  • University of Nebraska-Collaboration Initiative (402038/2023-1, APQ-01057–23, Finance Code 001, 1736030)
  • Algal Virus Research Funds from the University of Nebraska Foundation (402038/2023-1, APQ-01057–23, Finance Code 001, 1736030)

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