Nitrification, the two-step transformation of ammonia via nitrite to nitrate plays a significant role in the global nitrogen cycle. Ammonia oxidation, the first and rate-limiting reaction, is typically being mediated by ammonia oxidizing bacteria (AOB) and ammonia oxidizing archaea (AOA), followed by nitrite oxidizing bacteria (NOB) converting nitrite to nitrate. Relatively recently, specific bacteria of the genus Nitrospira were found to be capable of complete ammonia oxidation (comammox). While nitrification is used to reduce the concentration of nutrients in wastewater treatment plants, it can also lead to eutrophication of water bodies by transforming fertilizer-derived ammonia to leachable nitrate. Furthermore, nitrification is a source of the potent greenhouse gas nitrous oxide.

This project focuses on understanding nitrifier-virus interactions in a range of habitats and aims to characterize the impact of viruses on their respective hosts and the underlying ecosystem function. We isolated a bacteriophage infecting the nitrifying bacterium Nitrosomonas europaea and are now investigating its infection cycle and its effect on ammonia oxidation. The virus has a typical podoviral morphology with a capsid sized approximately 60 nm in diameter. It possesses a ca. 42 kb large genome, causes lytic infections which severely alter host-morphology and belongs to the family Autographiviridae. Recently, we were able to isolate two additional bacteriophages infecting Nitrosomonas europaea or Nitrosospira multiformis, respectively. Currently, we are in the process of isolating a fourth virus infecting a novel proposed type-strain of the genus Nitrosomonas.