Community composition of ammonia-oxidizing archaea from surface and anoxic depths of oceanic oxygen minimum zones

Xuefeng Peng,Amal Jayakumar,Bess B Ward

doi:10.3389/fmicb.2013.00177

Abstract

Ammonia-oxidizing archaea (AOA) have been reported at high abundance in much of the global ocean, even in environments, such as pelagic oxygen minimum zones (OMZs), where conditions seem unlikely to support aerobic ammonium oxidation. Due to the lack of information on any potential alternative metabolism of AOA, the AOA community composition might be expected to differ between oxic and anoxic environments. This hypothesis was tested by evaluating AOA community composition using a functional gene microarray that targets the ammonia monooxygenase gene subunit A (amoA). The relationship between environmental parameters and the biogeography of the Arabian Sea and the Eastern Tropical South Pacific (ETSP) AOA assemblages was investigated using principal component analysis (PCA) and redundancy analysis (RDA). In both the Arabian Sea and the ETSP, AOA communities within the core of the OMZ were not significantly different from those inhabiting the oxygenated surface waters above the OMZ. The AOA communities in the Arabian Sea were significantly different from those in the ETSP. In both oceans, the abundance of archaeal amoA gene in the core of the OMZ was higher than that in the surface waters. Our results indicate that AOA communities are distinguished by their geographic origin. RDA suggested that temperature (higher in the Arabian Sea than in the ETSP) was the main factor that correlated with the differences between the AOA communities. Physicochemical properties that characterized the different environments of the OMZ and surface waters played a less important role, than did geography, in shaping the AOA community composition.

Highlights

Nitrification plays a critical role in the marine nitrogen (N) cycle because it links the major sources and sinks of fixed reactive N by transforming ammonium to nitrite and subsequently nitrate
PHYSICOCHEMICAL PROPERTIES There was a large temperature gradient (∼10◦C) between the surface and the core of the oxygen minimum zones (OMZs) in the Arabian Sea, while the temperature difference was smaller in the Eastern Tropical South Pacific (ETSP) (Table 1)
Dissolved oxygen concentrations were below detection in the core of the OMZ where an accumulation of nitrite was observed in both the Arabian Sea and the ETSP

Summary

Introduction

Nitrification plays a critical role in the marine nitrogen (N) cycle because it links the major sources (nitrogen fixation) and sinks (denitrification) of fixed reactive N by transforming ammonium to nitrite and subsequently nitrate. The number of amoA gene copies per cell is reported to vary in the environment (Wuchter et al, 2006a; Agogue et al, 2008), the correlation between Thaumarchaeotal amoA and 16S rRNA gene abundances in the Arabian Sea indicates that most of the Thaumarchaeota are AOA (Pitcher et al, 2011). The dominant role of AOA in ammonia-oxidation in the ocean is supported by a positive correlation between their abundance (implied from abundance of amoA or 16S rRNA genes) and ammonia-oxidation rates, observed in the Gulf of California (Beman et al, 2008), the North Sea (Wuchter et al, 2006a), and the coastal eastern Pacific (Santoro et al, 2010). There is evidence from the Southern California Bight (Ward, 1987), and the Gulf of California (Beman et al, 2008) that the abundance of AOB is decoupled from nitrification rates in the ocean

Methods

Results

Conclusion