Transcriptomic response ofNitrosomonas europaeatransitioned from ammonia- to oxygen-limited steady-state growth

Abstract

word count: 250 34 Text word count: 4885 35 36 3 Abstract 37Ammonia-oxidizing microorganisms perform the first step of nitrification, the oxidation of 38 ammonia to nitrite. The bacterium Nitrosomonas europaea is the best characterized ammonia oxidizer to 39 date. Exposure to hypoxic conditions has a profound effect on the physiology of N. europaea, e.g. by 40 inducing nitrifier denitrification, resulting in increased nitric and nitrous oxide production. This metabolic 41 shift is of major significance in agricultural soils, as it contributes to fertilizer loss and global climate 42 change. Previous studies investigating the effect of oxygen limitation on N. europaea have focused on 43 the transcriptional regulation of genes involved in nitrification and nitrifier denitrification. Here, we 44 combine steady-state cultivation with whole genome transcriptomics to investigate the overall effect of 45 oxygen limitation on N. europaea. Under oxygen-limited conditions, growth yield was reduced and 46 ammonia to nitrite conversion was not stoichiometric, suggesting the production of nitrogenous gases. 47However, the transcription of the principal nitric oxide reductase (cNOR) did not change significantly 48 during oxygen-limited growth, while the transcription of the nitrite reductase-encoding gene (nirK) was 49 significantly lower. In contrast, both heme-copper containing cytochrome c oxidases encoded by N. 50 europaea were upregulated during oxygen-limited growth. Particularly striking was the significant 51 increase in transcription of the B-type heme-copper oxidase, proposed to function as a nitric oxide 52 reductase (sNOR) in ammonia-oxidizing bacteria. In the context of previous physiological studies, as well 53 as the evolutionary placement of N. europaea's sNOR with regards to other heme-copper oxidases, 54 these results suggest sNOR may function as a high-affinity terminal oxidase in N. europaea and other 55 AOB. 56 4 Importance 57 Nitrification is a ubiquitous, microbially mediated process in the environment and an essential 58 process in engineered systems such as wastewater and drinking water treatment plants. However, 59 nitrification also contributes to fertilizer loss from agricultural environments increasing the eutrophication 60 of downstream aquatic ecosystems and produces the greenhouse gas nitrous oxide. As ammonia-61 oxidizing bacteria are the most dominant ammonia-oxidizing microbes in fertilized agricultural soils, 62 understanding their response to a variety of environmental conditions is essential for curbing the 63 negative environmental effects of nitrification. Notably, oxygen limitation has been reported to 64 significantly increase nitric oxide and nitrous oxide production during nitrification. Here we investigate the 65 physiology of the best characterized ammonia-oxidizing bacterium, Nitrosomonas europaea, growing 66 under oxygen-limited conditions. 67 5 1 Introduction 68Nitrification is a microbially mediated, aerobic process involving the successive oxidation of 69 ammonia (NH 3 ) and n...

Growth of soil ammonia-oxidizing archaea on air-exposed solid surface

“…Depending on the environmental conditions, the various amoC homologs in the genome might provide different activity profiles to the AMO complex. Previous transcriptional studies showed that additional monocistronic amoC subunits found in some terrestrial AOB aid in maintaining AMO enzyme stability during stressful conditions [78][79][80]. Together, our findings suggest a pivotal role of the amoC3 gene in the ammonia oxidation activity of N. viennensis EN76 grown on air-exposed solid surfaces.…”

Revealing taxon-specific heavy metal-resistance mechanisms in denitrifying phosphorus removal sludge using genome-centric metaproteomics

“…2c and 3a). Similarly, the AMO transcriptions were observed increased in Nitrosomonas europaea pure cultures during oxygen-limited growth [73] and a nitrifying enrichment culture when its SOUR was constrained by heavy metals [9]. Overproduced AMO may contribute to the maintenance of ammonia oxidization under Cr pressure [74].…”