ABSTRACT
This chapter describes the methods which are designed to be used for the enumeration and isolation of viral pathogens that infect aquatic bacteria, cyanobacteria, and phytoplankton. Basically, four methods are used for enumerating viruses in aquatic environments. These are plaque assays, most-probable-number assays (MPNs), transmission electron microscopy (TEM), and epifluorescence microscopy. Unless viruses infecting the host are abundant, the chances of isolating one directly by plaque or MPN assays are slim; hence, the probability of finding a virus increases with the volume of water screened. Plaque assays are routinely used to estimate titers of viruses that cause lysis of bacteria, cyanobacteria, and algae that can be grown on solid media. MPNs are usually done to determine the concentration of lytic viruses that infect hosts which cannot be grown on solid medium but which can be grown in liquid. This is particularly a problem with delicate phytoplankton.
