The environmental controls that govern the end product of bacterial nitrate respiration

Abstract

In the biogeochemical nitrogen cycle, microbial respiration processes compete for nitrate as an electron acceptor. Denitrification converts nitrate into nitrogenous gas and thus removes fixed nitrogen from the biosphere, whereas ammonification converts nitrate into ammonium, which is directly reusable by primary producers. We combined multiple parallel long-term incubations of marine microbial nitrate-respiring communities with isotope labeling and metagenomics to unravel how specific environmental conditions select for either process. Microbial generation time, supply of nitrite relative to nitrate, and the carbon/nitrogen ratio were identified as key environmental controls that determine whether nitrite will be reduced to nitrogenous gas or ammonium. Our results define the microbial ecophysiology of a biogeochemical feedback loop that is key to global change, eutrophication, and wastewater treatment.

Expanded metabolic versatility of ubiquitous nitrite-oxidizing bacteria from the genus Nitrospira

“…S1A and SI Results and Discussion). Various forms of OCCs have been linked to assimilatory or dissimilatory nitrite reduction in other organisms (2,45). Intriguingly, N. moscoviensis might link nitrite reduction to ammonia by the OCC with energy conservation by proton translocation across the cell membrane (SI Results and Discussion).…”

“…Based on genomic and experimental data from Nitrospira moscoviensis representing the ubiquitous Nitrospira lineage II, we identified ecophysiological traits that contribute to the ecological success of Nitrospira. Unexpectedly, N. moscoviensis possesses genes coding for a urease and cleaves urea to ammonia and CO 2 . Ureolysis was not observed yet in nitrite oxidizers and enables N. moscoviensis to supply ammonia oxidizers lacking urease with ammonia from urea, which is fully nitrified by this consortium through reciprocal feeding.…”

“…The ammonia-oxidizing microorganisms (bacteria and archaea; AOM) oxidize ammonia to nitrite, which is subsequently oxidized to nitrate by nitriteoxidizing bacteria (NOB). Nitrification links aerobic and anaerobic pathways of the N cycle by providing nitrate or nitrite as electron acceptors for dissimilatory nitrate reduction, denitrification, respiratory ammonification, and anaerobic ammonium oxidation (1,2). The end product of nitrification, nitrate, is an important source of nitrogen for assimilation by many microorganisms and plants.…”

Activity, abundance and community structure of anammox bacteria along depth profiles in three different paddy soils

“…Compared to autotrophic anammox bacteria, heterotrophic denitrification bacteria are apparently more active and responsive to organic-rich environments such as flooded soils and sediments . Furthermore, previous studies have found that a relatively low C/N ratio is favored to denitrification while the opposite is true for anammox (Tiedje et al, 1982;Schmidt et al, 2011;Kraft et al, 2014). Due to the frequent N fertilizer application in agriculture, the paddy soils system received much more N input than marine system and resulted in a low C/N value, which might explain the reason of denitrification over anammox in paddy soils.…”

Subsurface nitrate reduction under wetlands takes place in narrow superficial zones

“…DNRA are less understood than denitrification although it can be a significant or even a dominant process in some ecosystems, [25]. Conditions favouring DNRA may include high temperature [26] and high C/N ratio, [27]. [28].…”