Characterization of temperate cyanophages active against freshwater phycocyanin-rich Synechococcus species

1. This study addressed the prevalence of lysogeny within 19 strains of freshwater Synechococcus sp. rich in phycocyanin (PC) that were isolated from a temperate lake or obtained, in four cases, from a culture collection. 2. Lysis of 16 Synechococcus strains (84%) was inducible with mitomycin C, but the required concentration (20 μg mL⁻¹) was higher than in other studies. Mitomycin C induction yielded burst sizes of 3.5-23.7 phages per cell. 3. Transmission Electron Microscopy of the resultant temperate phages showed that all belonged to the family Siphoviridae with capsid diameters ranging from 40.3 to 53.5 nm and tail lengths from 129 to 186 nm. None of the cyanophages could be maintained in the lytic cycle using the three non-lysogenic strains, or any of the other 16 lysogenic strains of Synechococcus. 4.These results suggest a potentially high level of lysogeny within PC-rich Synechococcus species in natural freshwaters, but that the presence of these temperate cyanosiphoviruses may go undetected with the lower mitomycin C concentrations commonly used.