Phage imbalances may disrupt wastewater treatment

In findings published this year in Water Research X, scientists from Sweden’s Chalmers University of Technology report that viruses may pose a previously unrecognized threat to some of our most important tamed species: The bacteria in our wastewater treatment plants.

A healthy wastewater treatment plant teems with tireless but benign prokaryotes. By devouring all the let’s-call-it-food in household and industrial effluent, they leave nothing left for harmful bacteria to grow on. Bacteriophages and other factors can kill some of these bacteria, affecting the efficiency of the treatment process in a phenomenon called a “viral shunt.”

“A large treatment plant has billions of bacteria that work in a treatment process called ‘activated sludge.’ The bacterial communities are constantly exposed to viruses that infect them, so the question we asked ourselves was whether the process can periodically be more exposed and what happens then,” says study co-author Professor Oskar Modin.

In this work, the research team recorded the concentrations of organic carbon and virus-like particles in the activated sludge (and if that isn’t your favorite euphemism ever, it should be) from four wastewater treatment plants in Sweden. They found a direct, linear relationship between the two: The more viruses, the more organic carbon

Since the point of a wastewater treatment plant is to reduce the amount of dissolved organic carbon, this is bad. High-carbon waste, once released, is eaten by wild microorganisms that, even if not themselves dangerous, will use up oxygen to do it. This causes oxygen levels in streams and waterways to drop, killing aerobic organisms.

The researchers noted that the increase in dissolved organic carbon was greater than the amount of carbon in the bodies of the phages themselves. The team concluded that, when the phages lysed the plant bacteria as part of their life cycle, they caused them to literally spill their carbon-rich prokaryotic guts back into their environment.

The team found many different types of viruses and bacteriophages in the sludge. The three largest groups were Siphoviridae, Myoviridae, and Podoviridae.

Read the full text of the paper in Water Research X.

Modin O, Fuad N, Abadikhah M, l’Ons D, Ossiansson E, Gustavsson DJI, Edefell E, Suarez C, Persson F, Wilén B-M. A relationship between phages and organic carbon in wastewater treatment plant effluents. Water Research X. 2022;16. doi: 10.1016/j.wroa.2022.100146