Genomic Variation, Host Range, and Infection Kinetics of Closely Related Cyanopodoviruses from New England Coastal Waters

Viruses infecting marine Synechococcus are abundant in coastal marine environments and influence the community composition and abundance of their cyanobacterial hosts. In this study, we focused on the cyanopodoviruses which have smaller genomes and narrower host ranges relative to cyanomyoviruses. While previous studies have compared the genomes of diverse podoviruses, here we analyzed the genomic variation, host ranges, and infection kinetics of podoviruses within the same OTU. The genomes of fifty-five podoviral isolates from the coastal waters of New England were fully sequenced. Based on DNA polymerase gene sequences, these isolates fall into five discrete OTUs (termed RIP – Rhode Island Podovirus). Although all the isolates belonging to the same RIP have very similar DNA polymerase gene sequences (>98% sequence identity), differences in genome content, particularly in regions associated with tail fiber genes, were observed among isolates in the same RIP. Host range tests reveal variation both across and within RIPs. Notably within RIP1, isolates that had similar tail fiber regions also had similar host ranges. Isolates belonging to RIP4 do not contain the host-derived psbA photosynthesis gene, while isolates in the other four RIPs do possess a psbA gene. Nevertheless, infection kinetic experiments suggest that the latent period and burst size for RIP4 isolates are similar to RIP1 isolates. We are continuing to investigate the correlations among genome content, host range, and infection kinetics of isolates belonging to the same OTU. Our results to date suggest that there is substantial genomic variation within an OTU and that this variation likely influences cyanopodoviral – host interactions.