Chloroviruses are common in inland waters throughout the
world with titers as high as thousands of plaque-forming units
(PFUs) per milliliter of indigenous water, although titers are
typically 1–100 PFUs/mL. The viruses cannot infect zoochlorellae
when they are in their symbiotic phase, and we have no
evidence that the zoochlorellae grow free of their hosts in
indigenous waters.