Characterization of incubation experiments and development of an enrichment culture capable of ammonium oxidation under iron-reducing conditions

S Huang,P R Jaffé

doi:10.5194/bg-12-769-2015

Abstract

Abstract. Incubation experiments were conducted using soil samples from a forested riparian wetland where we have previously observed anaerobic ammonium oxidation coupled to iron reduction. Production of both nitrite and ferrous iron was measured repeatedly during incubations when the soil slurry was supplied with either ferrihydrite or goethite and ammonium chloride. Significant changes in the microbial community were observed after 180 days of incubation as well as in a continuous flow membrane reactor, using 16S rRNA gene PCR-denaturing gradient gel electrophoresis, 454 pyrosequencing, and real-time quantitative PCR analysis. We be Acidimicrobiaceae bacterium A6), belonging to the Acidimicrobiaceae family, whose closest cultivated relative is Ferrimicrobium acidiphilum (with 92% identity) and Acidimicrobium ferrooxidans (with 90% identity), might play a key role in this anaerobic biological process that uses ferric iron as an electron acceptor while oxidizing ammonium to nitrite. After ammonium was oxidized to nitrite, nitrogen loss proceeded via denitrification and/or anammox.

Highlights

IntroductionThe most common removal of nitrogen from soil environments is mineralization (for organic nitrogen), followed by nitrification and denitrification (Canfield et al, 2010)
The most common removal of nitrogen from soil environments is mineralization, followed by nitrification and denitrification (Canfield et al, 2010)
2.7 Quantitative PCR assay quantitative PCR (qPCR) experiments were carried out using a StepOnePlusTM Real-Time PCR System (Life Technologies, USA), represented by 16S rRNA genes, using primer sets 1055f/1392r for total bacteria (Harms et al, 2003), Amx368f/Amx820r for anammox bacteria (Schmid et al, 2000; Schmid et al, 2003), acd320f–432r, which we developed for www.biogeosciences.net/12/769/2015/

Summary

Introduction

The most common removal of nitrogen from soil environments is mineralization (for organic nitrogen), followed by nitrification and denitrification (Canfield et al, 2010). A novel anaerobic NH+4 oxidation process coupled to iron reduction was first noted in a forested riparian wetland in New Jersey (Clement et al., 2005) In this reaction, NH+4 is the electron donor, which is oxidized to nitrite (NO−2 ), and ferric iron – Fe(III) – is the electron acceptor, which is reduced to ferrous iron – Fe(II). Using labeled 15NH+4 in a microcosm experiment resulted in the production of 15N2, which conclusively showed that ammonium-N was converted to nitrogen gas (N2) in these sediments under iron-reducing conditions (Shrestha et al, 2009) Either this same pathway for NH+4 oxidation, or a very similar one, was observed in a biological reactor (Sawayama, 2006) and a tropical rainforest soil (Yang et al, 2012), and coined Feammox (Sawayama, 2006). These pathways have been reported to oxidize NH+4 to NO−2 (Clement et al, 2005; Shrestha et al, 2009), to NO−3 (Sawayama, 2006), or directly to N2 (Yang et al, 2012), using Fe(III) as an electron acceptor

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Results

Conclusion