Diversity and evolution of the emerging Pandoraviridae family

Abstract

With DNA genomes up to 2.5 Mb packed in particles of bacterium-like shape and dimension, the first two Acanthamoeba-infecting Pandoraviruses remained the most spectacular viruses since their description in 2013. Our isolation of three new strains from distant locations and environments allowed us to perform the first comparative genomics analysis of the emerging worldwide-distributed Pandoraviridae family. Thorough annotation of the genomes combining transcriptomic, proteomic, and bioinformatic analyses, led to the discovery of many non-coding transcripts while significantly reducing the former set of predicted protein-coding genes. We found that the Pandoraviridae exhibit an open pan genome, the enormous size of which is not adequately explained by gene duplications or horizontal transfers. As most of the strain specific genes have no extant homolog and exhibit statistical features comparable to intergenic regions, we suggests that de novo gene creation is a strong component in the evolution of the giant Pandoravirus genomes.