The do-it-all nitrifier

Abstract

The discovery of bacteria that can oxidize both ammonia and nitrite upends a long-held dogma With numerous amendments to the microbial nitrogen cycle over the past two decades, it seems at times that nothing is certain. Yet one aspect of the nitrogen cycle seemed clear: that the labor of nitrification—the oxidation of ammonia (NH 3 ) to nitrite (NO 2 − ) and ultimately nitrate (NO 3 − )—is divided between two separate groups of microorganisms. Sergei Winogradsky first showed this in the late 1800s when he isolated the organisms responsible for the two steps of nitrification, ammonia oxidizers and nitrite oxidizers. But a series of recent papers upends this 100-year-old dogma with the description of three different cultivated bacteria ( 1 , 2 ) and an uncultivated bacterium ( 3 ) that can each carry out the complete oxidation of ammonia to nitrate.