Temporal transcriptomes of a marine cyanopodovirus and its Synechococcus host during infection

Marine picocyanobacteria belonging to genera Synechococcus and Prochlorococcus are genetically diverged and distributed into distinct biogeographical patterns, and both are infected by genetically closely related cyanopodoviruses. Previous studies have not fully explored whether the two virus-host systems share similar gene expression patterns during infection. Whole-genome expression dynamics of T7-like cyanopodovirus P-SSP7 and its host Prochlorococcus strain MED4 have already been reported. Here, we conducted genomic and transcriptomic analyses on T7-like cyanopodovirus S-SBP1 during its infection on Synechococcus strain WH7803. S-SBP1 has a latent period of 8 h and phage DNA production of 30 copies per cell. In terms of whole-genome phylogenetic relationships and average nucleotide identity, S-SBP1 was most similar to cyanopodovirus S-RIP2, which also infects Synechococcus WH7803. Three hypervariable genomic islands were identified when comparing the genomes of S-SBP1 and S-RIP2. Single nucleotide variants were also observed in three S-SBP1 genes, which were located within the island regions. Based on RNA-seq analysis, S-SBP1 genes clustered into three temporal expression classes, whose gene content was similar to that of P-SSP7. Thirty-two host genes were upregulated during phage infection, including those involved in carbon metabolism, ribosome components, and stress response. These upregulated genes were similar to those upregulated by Prochlorococcus MED4 in response to infection by P-SSP7. Our study demonstrates a programmed temporal expression pattern of cyanopodoviruses and hosts during infection.