Recovery of viable cyanophages from the sediments of a eutrophic lake at decadal timescales.

Cyanobacteria and their associated viruses (cyanophages) are abundant throughout the world in both marine and freshwater environments. The predator-prey relationship influences population dynamics within these ecosystems and facilitates the co-evolution of both organisms. Evidence of the close-linked interactions between cyanobacteria and viruses has been found extensively throughout marine biomes, but freshwater systems are less well studied. Eutrophic lake sediments potentially allow the preservation of cyanophages. If historic cyanophages could be isolated, they could provide insights into the evolution, biology and population dynamics over defined timescales. To determine whether viable phages are present in this environment, sectioned sediment cores (~ 50 cm in length) were taken from a eutrophic, stratifying lake (Rostherne Mere, Cheshire, UK). They were examined under the transmission electron microscope, and phages were isolated on two Microcystis strains PCC 7820 and BC 84/1. Viable phages were recovered from ~ 33- and ~ 50-year-old sediments. This is the first known study to investigate the viability of freshwater cyanophages recovered from dated lake sediments.