Name: Yazeed Ibrahim

Email: ibrahimy@uci.edu

Author: Yazeed Ibrahim, China Hanson, Claudia Weihe, and Jennifer Martiny

Author affiliation: Department of Ecology and Evolutionary Biology, University of California, Irvine, USA

Abstract title: Host range patterns in Synechococcus spp. Cyanophages: Linking genotype and phenotype

Absstract:

Cyanophages are highly genetically diverse in surface seawater. The relationship between this genetic diversity and the ability of a phage to infect a particular range of hosts ? one aspect of a phage?s phenotype ? remains unclear. Most studies of the genetic diversity of marine cyanophages target g20, a gene encoding a capsid structure protein. Previous studies demonstrate that the similarity between the g20 alleles of two cyanophages is not correlated with the similarity of their host range phenotypes, suggesting that the genes underlying host range evolve much faster than the g20 gene. This result does not preclude a relationship between g20 genotype and a phage?s phenotype in a particular community, however. On short time and spatial scales, g20 may be a marker of the most abundant phage clones in a population, such that the same g20 allele will be associated with the same host range phenotype. If so, the diversity of g20 alleles in a water sample would indicate the diversity of host range phenotypes. In this study, we test whether the g20 gene of Synechococcus cyanophages is related to their infection phenotype over short time and spatial scales in natural communities. Using a dilution to extinction method, we isolated nearly 450 cyanophages on Synechococcus WH7803 from three locations along the southern California coast during the months of June, July, and August in 2008. To assay cyanophage genotypes, we plaque-purified each isolate, then sequenced the g20 gene. To determine host range phenotypes, we will perform infectivity assays of each isolate on each of different Synechococcus host strains (WH8101, WH8012, WH8018) in replicate microtiter wells. After two weeks of incubation, we will visually examine the plates to detect cell lysis, and these observations will be used to determine each isolate?s host range phenotype. We predict that isolates from a water sample with the same g20 genotype will have the same infectivity profile, and thus that g20 diversity will correlate with phenotype diversity. Because of rapid mixing of coastal surface waters, we further hypothesize that phages with the same g20 allele isolated on the same day from nearby sampling locations will have similar phenotypes. In contrast, we do not expect that isolates with similar g20 alleles sampled during different months will have the same phenotype, as host range phenotype likely evolve over a month.