Phylogenetic Diversity of Sequences of Cyanophage Photosynthetic Gene psbA in Marine and Freshwaters

Many cyanophage isolates which infect the marine cyanobacteriaSynechococcus spp. andProchlorococcus spp. contain a gene homologous topsbA , which codes for the D1 protein involved in photosynthesis. In the present study, cyanophagepsbA gene fragments were readily amplified from freshwater and marine samples, confirming their widespread occurrence in aquatic communities. Phylogenetic analyses demonstrated that sequences from freshwaters have an evolutionary history that is distinct from that of their marine counterparts. Similarly, sequences from cyanophages infectingProchlorococcus andSynechococcus spp. were readily discriminated, as were sequences from podoviruses and myoviruses. ViralpsbA sequences from the same geographic origins clustered within different clades. For example, cyanophagepsbA sequences from the Arctic Ocean fell within theSynechococcus as well asProchlorococcus phage groups. Moreover, aspsbA sequences are not confined to a single family of phages, they provide an additional genetic marker that can be used to explore the diversity and evolutionary history of cyanophages in aquatic environments.