Many bacteria riddled with viruses.

Many bacteria riddled with viruses

A painstaking new study in which researchers sliced through thousands of ocean-dwelling bacteria and photographed the cross-sections indicates that a large percentage of the microscopic cells harbor viral infections. The research confirms a growing suspicion among scientists that viruses play a much more important role in marine ecology than previously believed.

Until recently, researchers assumed that most aquatic bacteria succumbed to "grazing" by protozoans. But last summer, Norwegian researchers identified unexpectedly high numbers of viruses in both marine and freshwater environments (SN: 8/12/89, p.100), leading them to hypothesize that viruses may cause much of the bacterial death in these waters. The potential implications of large-scale viral infection in aquatic bacteria are substantial -- including higher-than-expected carbon and nitrogen turnover at the bottom of the food chain and an increased possibility of virus-mediated genetic exchange among bacterial cells. But there remained no direct evidence that many bacteria were actually becoming infected.

Now, Lita M. Proctor and Jed A. Fuhrman of the University of Southern California in Los Angeles provide that evidence in a series of electron micrographs. They report in the Jan. 4 NATURE that 15 to 30 percent of the marine bacteria they sliced and photographed were infected with viruses. Infected bacteria contained 10 to 100 or more mature viruses each.

The researchers note that their photographic technique missed large areas of each cell that may harbor viruses. All told, they estimate that as many as 70 percent of marine bacterial cells could be infected. And on the basis of other reports of bacterial mortality rates from viral infection, they conclude that such infections may account for a surprising 30 to 60 percent of bacterial mortality in ocean environs.