The production of nitric oxide by marine ammonia‐oxidizing archaea and inhibition of archaeal ammonia oxidation by a nitric oxide scavenger

Abstract

Nitrification is a critical process for the balance of reduced and oxidized nitrogen pools in nature, linking mineralization to the nitrogen loss processes of denitrification and anammox. Recent studies indicate a significant contribution of ammonia-oxidizing archaea (AOA) to nitrification. However, quantification of the relative contributions of AOA and ammonia-oxidizing bacteria (AOB) to in situ ammonia oxidation remains challenging. We show here the production of nitric oxide (NO) by Nitrosopumilus maritimus SCM1. Activity of SCM1 was always associated with the release of NO with quasi-steady state concentrations between 0.05 and 0.08 μM. NO production and metabolic activity were inhibited by the nitrogen free radical scavenger 2-phenyl-4,4,5,5,-tetramethylimidazoline-1-oxyl-3-oxide (PTIO). Comparison of marine and terrestrial AOB strains with SCM1 and the recently isolated marine AOA strain HCA1 demonstrated a differential sensitivity of AOB and AOA to PTIO and allylthiourea (ATU). Similar to the investigated AOA strains, bulk water column nitrification at coastal and open ocean sites with sub-micromolar ammonia/ammonium concentrations was inhibited by PTIO and insensitive to ATU. These experiments support predictions from kinetic, molecular and biogeochemical studies, indicating that marine nitrification at low ammonia/ammonium concentrations is largely driven by archaea and suggest an important role of NO in the archaeal metabolism.

Pathways and key intermediates required for obligate aerobic ammonia-dependent chemolithotrophy in bacteria and Thaumarchaeota

“…NO is produced and immediately consumed during active ammonia oxidation by N. viennensis EN76 T The initial, rapid production of NO followed by its equally rapid consumption during ammonia-dependent O 2 consumption by N. viennensis differed from results in similar experiments with N. maritimus SCM1 (Martens-Habbena et al, 2015). In this prior study, N. maritimus SCM1 produced NO at a steady-state level prior to its consumption once NH 4 + was depleted or its partial consumption at saturating concentrations of NH 4 + .…”

“…Martens-Habbena et al (2015) demonstrated that NO accumulated in N. maritimus SCM1 cultures during active oxidation of NH 4 Cl in a closed microrespirometry chamber, and was released at higher levels under saturating versus non-saturating availability of NH 4 Cl. Exposure to increasing concentrations of an NO-scavenging compound over a 24 h period resulted in decreased levels of nitrite production in batch cultures of ammonia-oxidizing Thaumarchaea, but not bacteria (Martens-Habbena et al, 2015). The authors concluded that NO was either released as a free intermediate during ammonia oxidation by N. maritimus, or it could serve a functional role as an electron delivery mechanism to ammonia monooxygenase, an idea that has been proposed previously .…”

“…In ammoniaoxidizing bacteria, this second step is performed by hydroxylamine dehydrogenase (EC 1.7.2.6); however, no homologues of hydroxylamine dehydrogenaseencoding genes have been identified in genome sequences obtained from any pure or enrichment culture of Thaumarchaea (Walker et al, 2010;Kim et al, 2011;Tourna et al, 2011;Spang et al, 2012). In addition to NH 2 OH, there is also evidence that nitric oxide (NO) plays an important role in the Thaumarchaeotal but not in the bacterial ammonia oxidation pathway (Shen et al, 2013;Martens-Habbena et al, 2015). Martens-Habbena et al (2015) demonstrated that NO accumulated in N. maritimus SCM1 cultures during active oxidation of NH 4 Cl in a closed microrespirometry chamber, and was released at higher levels under saturating versus non-saturating availability of NH 4 Cl.…”

“…In addition to NH 2 OH, there is also evidence that nitric oxide (NO) plays an important role in the Thaumarchaeotal but not in the bacterial ammonia oxidation pathway (Shen et al, 2013;Martens-Habbena et al, 2015). Martens-Habbena et al (2015) demonstrated that NO accumulated in N. maritimus SCM1 cultures during active oxidation of NH 4 Cl in a closed microrespirometry chamber, and was released at higher levels under saturating versus non-saturating availability of NH 4 Cl. Exposure to increasing concentrations of an NO-scavenging compound over a 24 h period resulted in decreased levels of nitrite production in batch cultures of ammonia-oxidizing Thaumarchaea, but not bacteria (Martens-Habbena et al, 2015).…”

Confounding effects of oxygen and temperature on the TEX 86 signature of marine Thaumarchaeota

“…They are generally recognized as the main drivers of oceanic nitrification (5)(6)(7), are closely coupled with anammox organisms in oxygen minimum zones (OMZs) (8)(9)(10), and have been implicated as a source of the greater part of oceanic emissions of the ozone-depleting greenhouse gas nitrous oxide (11). Their wide habitat range suggests both high ecotypic diversity and adaptive capacity (12,13).…”