Name: Andrew Millard

Email: a.d.millard@warwick.ac.uk

Author: Andrew D. Millard1*, K. Zwirglmaier1, Nicholas H. Mann1, David J. Scanlan1

Author affiliation: 1Department of Biological Sciences, University of Warwick, Gibbet Hill Road, Coventry, CV4 7AL, UK *Presenting author

Abstract title: Comparative genomics of marine cyanomyoviruses reveals the widespread occurrence of Synechococcus host genes localised to a hyperplastic region : implications for mechanisms of cyanophage evolution

Absstract:

Phages infecting marine cyanobacteria of the genera Synechococcus and Prochlorococcus are known to be as widely distributed in the oceans, as are their hosts. The vast majority of cyanophages isolated have been cyanomyoviruses, a group related to bacteriophage T4. To date, we have little idea of the core set of phage genes required to infect a cyanobacterial host or those genes that might be considered cyanophage-specific as opposed to phage-specific. By utilising a combination of bioinformatic and comparative genomic hybridisation approaches we aimed to identify components of the core and accessory genome of cyanomyoviurses, so as to provide further insights into the taxonomic and functional diversity of this group. The results of comparative genome analysis of five cyanomyoviruses, including the newly sequenced cyanophage S-RMS4, revealed a “core genome” of 64 genes, 48 of which were also found in other T4-like phages with 16 core genes specific to cyanophages. Subsequent comparative genomic hybridisation analysis using a pilot microarray showed that a number of ‘host’ genes were widespread in cyanomyovirus isolates. Furthermore, a hyperplastic region was identified between genes g15-g18, within a highly conserved structural gene module, which contained a variable number of inserted genes that lacked conservation in gene order. Several of these inserted genes were host-like and included ptoX, gnd, zwf and petE encoding plastoquinol terminal oxidase, 6-phosphogluconate dehydrogenase, glucose-6-phosphate dehydrogenase and plastocyanin, respectively. All of these genes potentially play a role in altering host photosynthetic function or carbon metabolism, thus increasing phage fitness. Phylogenetic analyses suggest that these genes were acquired independently of each other, even though they have become localised within the same genomic region. It appears that the hyperplastic region acquires genes whose fitness can then be tested prior to them becoming widespread in the cyanophage population e.g. genes of host origin like psbA, psbD and mazG. Whilst this hyperplastic region contains no detectable sequence features that might be mechanistically involved with the acquisition of host-like genes, it does appear to be a site specifically associated with the acquisition process and may represent a novel facet of the evolution of marine cyanomyoviruses.