Abstract
Mimivirus bradfordmassiliense (Mimivirus) is a giant virus that infects Acanthamoeba species - opportunistic human pathogens. Long- and short-read sequencing were used to generate a de novo transcriptome of the host and followed the dynamics of both host and virus transcriptomes over the course of infection. The assembled transcriptome of the host included 22,604 transcripts and 13,043 genes, with N50 = 2,372 nucleotides. Functional enrichment analysis revealed major changes in the host transcriptome, namely, enrichment in downregulated genes associated with cytoskeleton homeostasis and DNA replication, repair, and nucleotide synthesis. These modulations, together with those implicated by other enriched processes, indicate cell cycle arrest, which was demonstrated experimentally. We also observed upregulation of host genes associated with transcription, secretory pathways and, as reported here for the first time, peroxisomes and the ubiquitin-proteasome system. In Mimivirus, the early stages of infection were marked by upregulated genes related to DNA replication, transcription, translation, and nucleotide metabolism, and in later stages, enrichment in genes associated with lipid metabolism, carbohydrates, and proteases. Some of the changes observed in the amoebal transcriptome likely point to Mimivirus infection causing dismantling of host cytoskeleton and translocation of endoplasmic reticulum membranes to viral factory areas.