Fe⁰/Fe²⁺-Dependent Nitrate Reduction in Anammox Consortia Questions the Enzymatic Mechanism of Nitrate Reduction by Anammox Bacteria

Abstract

The anammox bacteria (AnAOB) have been suggested to perform dissimilatory Fe0/Fe2+-dependent nitrate reduction to ammonium (DNRA), with nitrite as intermediate. However, evidence at genetic and transcriptional levels for how AnAOB reduces nitrate is still lacking, making their roles in this process obscure and questionable. The short-term batch assays and long-term operation of bioreactor combined with 16S rDNA sequencing and transcription analysis were used for the first time to investigate the nitrate reduction pathway in anammox consortia. It is shown that AnAOB metabolically well grew with nitrate as the sole nitrogen source. They reduced nitrate to nitrite with highly expressed narG gene. However, the DNRA-enabling gene nrfA was not expressed by AnAOB. Abiotic reduction by Fe0/Fe2+ contributed to the nitrate and nitrite reduction to ammonium. The correlation analysis of microbial community structure and metabolic functions indicated that amino acid and carbohydrate transport and metabolism interactions in coexisting bacteria could facilitate the AnAOB growth with nitrate as the only nitrogen source. Our findings suggest that the contribution of enzymatic DNRA by AnAOB to the observed nitrate reduction has been probably overestimated in previous publications, and it should be questioned until the clear enzymatic mechanism responsible for nitrate reduction is identified.

Construction of Frustrated Lewis Pair Sites in CeO2–C/BiVO4 for Photoelectrochemical Nitrate Reduction

“…Ammonia (NH 3 ) is currently one of the most produced chemicals and renewable electricity carriers because of its high energy density (3 kW h kg –1 ) and hydrogen content (17.7 wt %). − The industrial production of NH 3 commonly requires harsh conditions and releases a large amount of CO 2 , which has prompted the search for environmentally green technologies. − Photoelectrochemical (PEC) technology integrates the comprehensive advantages of photochemistry and electrochemistry to reduce the harmful pollutant nitrate (NO 3 – ) in water to high value-added NH 3 . , Furthermore, the previous report demonstrated that the bacteria can successfully convert NO 3 – to NH 3 by the gene-encoded reductase under mild conditions, where the active sites of reductase were considered to be crucial for photoelectrochemical nitrate reduction reaction (PEC NIRR) . Therefore, the rational construction of active sites becomes a feasible approach to improve the kinetics of PEC NIRR. , …”

New Insight Into the Interspecies Shift of Anammox Bacteria Ca. “Brocadia” and Ca. “Jettenia” in Reactors Fed With Formate and Folate

“…While anammox bacteria grow well with nitrate as the sole nitrogen source, their ability to perform a complete DNRA process was questioned in the present study. Anammox bacteria were shown to express the narG gene for the reduction of nitrate to nitrite in Fe 0 /Fe 2+ -dependent partial DNRA, whereas ammonium was produced from nitrite by abiotic reduction, facilitated by Fe 0 and Fe 2+ (Bi et al, 2020).…”

Fabrication of an amorphous metal oxide/p-BiVO4 photocathode: understanding the role of entropy for reducing nitrate to ammonia

“…Ammonia (NH 3 ) is an important inorganic chemical product, which is widely used as a raw material in chemical fertilizers and industrial production. [1][2][3][4][5] However, industrial NH 3 production consumes a lot of fuel, while excess fertilizer in the ground leads to increased concentrations of nitrate (NO 3 − ) in groundwater, damaging the ecosystem. [6][7][8] Thus, the reduction of NO 3 − to NH 3 via environment-friendly technology is an ideal pathway to realize the recycling of nitrogen in fertilizer.…”