No. 66: Nov-Dec 1989
"The concentration of bacteriophages in natural unpolluted waters is in general believed to be low, and they have therefore been considered ecologically unimportant. Using a new method for quantitative enumeration, we have found up to 2.5 x 108 virus particles per millilitre in natural waters. These concentrations indicate that virus infection may be an important factor in the ecological control of planktonic microorganisms, and that viruses might mediate genetic exchange among bacteria in natural aquatic environments."
(Bergh, Oivind, et al; "High Abundance of Viruses Found in Aquatic Environments," Nature, 340:467, 1989.)
A sip of water could therefore introduce a billion virus particles into your stomach! This level of virus density in natural water is about 10 million times that formerly estimated.
Besides reducing your thirst, what are the implications of this discovery? First, it suggests that bacteria in natural waters are probably kept in check by viruses as well as protozoans. So far, this sounds good. Second, since viruses can ferry genetic material between organisms via transduction (i.e., host DNA is carried to the next host). This means that genes for antibody resistance and increased bacterial virulence (as present in sewage) may be spread quickly and widely. Also, "engineered bacteria" proposed for use in agriculture, viz., the ice-minus bacterium created to protect strawberries, may die, but their new genes will soon be everywhere.
(Weiss, R.; "Aquatic Viruses Unexpectedly Abundant," Science News, 136: 100, 1989.)