Cyanophages, viruses that infect cyanobacteria, are known to be abundant throughout the world’s oceans. They are important because of the ecological significance of their hosts which are prominent primary producers. In the natural environment cyanobacteria undergo light-dark cycles, which might be expected to exert significant effects on the way in which cyanophages reproduce. The results in this study show how light plays an important role in cyanophage adsorption to the host cell using a model system consisting of cyanophage S-PM2 and Synechococcus sp. WH7803. An initial investigation of the role of light on phage adsorption revealed a striking light-dependence. In the dark, the phage S-PM2 was virtually not capable of adsorbing to WH7803, but adsorption resumed as soon as the light was switched on. This light-dependent phage adsorption was not just limited to the phage S-PM2, four out of nine other cyanophages showed the same effect. The host photosynthetic activity and light/dark cycles were demonstrated not to influence phage adsorption. The presence of the photosynthetic reaction centre gene psbA in cyanophage genomes was not associated with the light-dependent phage adsorption. No photoreceptor was detected from the phage S-PM2 particle. A phage-resistant mutant that S-PM2 can’t adsorb to WH7803 was isolated. A putative multicopper oxidase was found to be absent from the outer membrane fraction of the mutant. This outer membrane fraction in the wild type showed a moderate phage neutralisation activity (up to ~ 30%). To test whether the putative multicopper oxidase was the S-PM2 receptor, a recombinant WH7803 strain was constructed by inactivating the putative multicopper oxidase gene. As S-PM2 can still adsorb to the knockout mutant as efficiently as to the wild type, it suggests that the multicopper oxidase is not the phage receptor and that loss of the putative multicopper oxidase is probably a pleiotropic consequence of the loss of the S-PM2 receptor or other components, such as lipopolysaccharide, that is needed for a successful S-PM2 adsorption
To submit an update or takedown request for this paper, please submit an Update/Correction/Removal Request.