Background/Question/Methods Viruses are the most abundant and diverse biological entities in the oceans. As agents of mortality, they contribute to biogeochemical cycling and influence the composition, diversity, and activity of prokaryotic host communities. Despite this, little is known about the factors that influence viral distribution and activity in the environment. Here, we investigate the spatial and temporal distribution of viruses (cyanophages) that infect the marine cyanobacterium, Synechococcus. We monitored the abundance and community structure of cyanophages each month for one year at a coastal location in southern California and for 10 years at a coastal location in Rhode Island.

Results/Conclusions Using a most-probable number approach, we found that patterns of cyanophage abundance at the two sites were similar. In particular, cyanophages on both coasts are seasonally dynamic, exhibiting highest abundance in the summer and decreased abundance in the winter with a slight increase mid-winter. To characterize cyanophage community structure over time, we isolated over 100 cyanophages each month for one year at several coastal locations in southern California and sequenced their g20 capsid protein genes. Preliminary sequence analysis of 250 isolates indicates that cyanophage phylogenetic composition differs significantly across months. Additionally, we examined spatial patterns in cyanophage communities by comparing the g20 sequences of California isolates to those of isolates from Rhode Island. Although identical g20 sequences are repeatedly observed over time at the Rhode Island location, isolates from the two coasts are at least 4% different in g20 nucleotide sequence. This implies that coastal marine cyanophage communities may be spatially distinct at a trans-oceanic scale. Overall our results suggest that coastal marine cyanophage communities are differentiated both temporally and spatially.