Name: Jessica Clasen

Email: jlclasen@uci.edu

Author: Jessica L. Clasen*, Claudia Weihe, and Jennifer B.H. Martiny

Author affiliation: Department of Ecology and Evolutionary Biology, University of California, Irvine, CA, USA *Presenting author

Abstract title: Temporal dynamics of psbA genes in a coastal cyanophage community

Absstract:

Marine cyanophage isolates often carry a gene (psbA) encoding a core photosynthetic protein (D1). The presence and expression of psbA appears to increase viral fitness. Evidence suggests that psbA genes are common, diverse and spatially variable amongst cyanophage; however, little is known about the temporal dynamics of this gene in marine communities. We investigated month-to-month variability in the presence, composition and diversity of psbA genes in cyanophage isolated from Southern California coastal seawaters. Every month for a year, ~150 cyanophage were isolated on Synechococcus WH7803, using dilution-to-extinction coupled with plaque purification techniques. The resulting phages were screened for the presence of psbA and amplicons were sequenced. Sequences were used to determine phylogenetic relationships and diversity statistics. Overall, psbA was present in >90% of the cyanophage isolates; however, there was a significant difference in this number across months (ANOVA, p=0.001). For example, psbA was amplified from <25% of the cyanophage isolated from April, suggesting a shift in community composition to cyanophage that do not carry psbA. Phylogenetic analysis indicated that a majority (62%) of the psbA sequences fell into the previously identified Marine 1 cluster, a cluster that contains marine myoviruses that infect Synechococcus. The remaining sequences (38%) formed two new well-supported clusters. We also detected substantial temporal variability in psbA diversity. For example, cyanophage isolated from July were more diverse than those from June based upon both Shannon and Simpson diversity indices. Furthermore, rarefaction curves indicated significant differences in psbA richness across months. Cyanophage psbA diversity appears to be positively correlated with the number of infectious cyanoviruses, suggesting viral abundance and psbA diversity may be linked. Overall, the abundance and diversity of cyanophage psbA genes appears to be highly dynamic in this phage community.