Document Type


Publication Date

Summer 2023


The prevalence of many nitrogen compounds has important consequences for human and ecosystem health. For example, too much nitrate in drinking water is globally a concern for human health, with the potential to cause disease in infants and adults (Lee Kwang-Sik 2008, Moldovan et al. 2020, Majumdar and Gupta 2000), and nitrous oxide is an exceptionally potent greenhouse gas (Zhang et al 2020). Many plants need fixed nitrogen, but as far as we have discovered, nitrogen is only fixed by bacteria and archaea. While there is existing literature on the metagenomics of nitrogen in certain individual ecosystems (e.g. Roco et al 2019) and the effects of specific pollutants on the soil nitrogen microbiome (e.g. Wang et al 2020), the impact of different soil environments on these nitrogen-cycling microorganismal populations remains relatively unstudied. There are three main processes involved in the nitrogen cycle for terrestrial environments: nitrogen fixation, nitrification, and denitrification (Zhang et al 2020). In nitrogen fixation, microbes fix dinitrogen gas (N2) into ammonia (NH3); in nitrification, microbes turn ammonia into nitrite (NO2-) and nitrite into nitrate (NO3-) (Zhang et al 2020). The third major process in the nitrogen cycle is denitrification, where nitrate is turned back into dinitrogen gas. Denitrification generally occurs because microorganisms run out of oxygen to use as an electron acceptor in respiration and instead use nitrate, reducing it to nitrite (NO2-), nitrous oxide (N2O), and nitrogen gas (N2), all of which have important environmental consequences (Zhang et al 2020). Other major sources of these forms of nitrogen include agricultural runoff, which is correlated with elevated nitrate concentrations (Lee Kwang-Sik 2008) and can increase prevalence of nitrogen genes in metagenomic data (Orellana et al 2018).



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