Inhibition of Bacterial Ammonia Oxidation by Organohydrazines in Soil Microcosms

Yucheng Wu,Zhongjun Jia,Wenhui Zhong,Yun Guo,Xiangui Lin

doi:10.3389/fmicb.2012.00010

Yucheng Wu, Zhongjun Jia + Show 3 more

Open Access

https://doi.org/10.3389/fmicb.2012.00010

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Abstract

Hydroxylamine oxidation by hydroxylamine oxidoreductase (HAO) is a key step for energy-yielding in support of the growth of ammonia-oxidizing bacteria (AOB). Organohydrazines have been shown to inactivate HAO from Nitrosomonas europaea, and may serve as selective inhibitors to differentiate bacterial from archaeal ammonia oxidation due to the absence of bacterial HAO gene homolog in known ammonia-oxidizing archaea (AOA). In this study, the effects of three organohydrazines on activity, abundance, and composition of AOB and AOA were evaluated in soil microcosms. The results indicate that phenylhydrazine and methylhydrazine at the concentration of 100 μmol g−1 dry weight soil completely suppressed the activity of soil nitrification. Denaturing gradient gel electrophoresis fingerprinting and sequencing analysis of bacterial ammonia monooxygenase subunit A gene (amoA) clearly demonstrated that nitrification activity change is well paralleled with the growth of Nitrosomonas europaea-like AOB in soil microcosms. No significant correlation between AOA community structure and nitrification activity was observed among all treatments during the incubation period, although incomplete inhibition of nitrification activity occurred in 2-hydroxyethylhydrazine-amended soil microcosms. These findings show that the HAO-targeted organohydrazines can effectively inhibit bacterial nitrification in soil, and the mechanism of organohydrazine affecting AOA remains unclear.

Highlights

Nitrification, the consecutive oxidation of ammonia to nitrate via nitrite, is one of the central processes in the global nitrogen cycle (Gruber and Galloway, 2008)
When compared to CK-N treatment, organohydrazines at low concentration of 1 μmol g−1 soil showed no inhibition on nitrification activity, it seemed that 31 and 16% of nitrification activity was eliminated under elevated concentration of 10 μmol organohydrazines g−1 soil for phenylhydrazine hydrochloride (PH)-M and methylhydrazine sulfate (MH)-M microcosms, respectively
Complete inhibition was observed at only high concentration of 100 μmol PH or MH g−1 soil, whereas a 7.2% of nitrification activity remained in HH-H microcosm

Summary

Introduction

Nitrification, the consecutive oxidation of ammonia to nitrate via nitrite, is one of the central processes in the global nitrogen cycle (Gruber and Galloway, 2008). The numerical dominance of ammonia-oxidizing archaea (AOA) over ammonia-oxidizing bacteria (AOB) appears to be a common feature in a wide variety of environments (Leininger et al, 2006; Agogué et al, 2008; Reed et al, 2010; Wu et al, 2010). The transcriptional activity and exceptionally high abundance of archaeal amoA gene in various habitats (Chen et al, 2008; Tourna et al, 2008; Church et al, 2010) have suggested AOA might play a key role in ammonia oxidation, there are some reports suggesting AOB dominate microbial ammonia oxidation in nitrogen-rich environment (Jia and Conrad, 2009; Xia et al, 2011). The relative contributions of AOA and AOB to nitrification activity in natural environment have attracted considerable attentions in recent years (Prosser and Nicol, 2008)

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