Floodplain nitrifiers harbor the genetic potential for utilizing a wide range of organic nitrogen compounds

Floodplains are critical ecosystems where terrestrial and riverine systems meet. Floodplain sediments experience many, sometimes dramatic, changes in moisture and oxygen concentrations because of changes in water table height, flooding, and drought, leading to active microbial cycling of contaminants and nutrients. Nitrogen is one such nutrient that is not only essential for the building blocks of life but can also be used as an energy source by some microorganisms. Microorganisms that oxidize ammonia and nitrite are a crucial part of the nitrogen cycle and can lead to eventual nitrogen loss from a system. Investigating the genes present in microorganisms responsible for nitrification in a dynamic floodplain suggests that organic nitrogen-from decaying plants or potentially other sources, such as fertilizers, grazing livestock feces, or contaminants (e.g., pesticides, pharmaceuticals)-is an important nitrogen source to these microorganisms. This study identifies genes not previously described in nitrifying microorganisms, expanding their potential metabolic substrates.