Water samples isolated from various sites were screened for the presence of algal viruses using the plaque assay. If viruses were not detected initially, an enrichment protocol was used in which a few algal cells were added to the water sample; after 48-72 hours the algal and cell debris were removed by centrifugation and the sample was reassayed for the presence of virus. Using these procedures, more than 50 individual algal viral isolates were identified. Although the viruses were all large polygonal particles with dsDNA genomes, analysis of the viral DNA by digestion with restriction endonucleases showed there were at least 15 different types of virus found. Sites that contained virus were further analyzed for the natural algal hosts; however, none were identified. It is unclear why the natural hosts could not be found. Dr. Meints proposed either that the viruses were propagated or maintained by some unknown mechanism, or, more likely, that the natural host was present in the sites tested at very low concentrations. This is possible in that each virus that infects an algal cell could produce 350 new virus particles, and that up to 100 algal cells can exist within a single Paramecium. Based on the density of viral particles isolated from the various sites, a single Paramecium with algal symbionts could theoretically sustain a virus population in 350 liters of water. Because a natural alga host for the viruses was not found, the goal of characterizing the viral host was dropped, and further screening efforts were discontinued.

In a separate, but related, series of experiments, Dr. Meints received 250 water samples collected by Dr. Ralph Lewin of the Scripps Institute in La Jolla, California. These were also screened for the presence of algal viruses, but viral particles were not found in any of Dr. Lewin’s samples.