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Chapter 9 : Distribution, Activity, and Ecology of Anammox Bacteria in Aquatic Environments
Category: Environmental Microbiology
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This chapter provides a synthesis of the broadscale patterns of anammox across a spectrum of aquatic ecosystems and to put forward some hypotheses as to what regulates anammox and the total flux of N in such systems. Research into anammox falls largely into two distinct aquatic ecosystems: (i) its role in the anaerobic oxidation of ammonium in the suboxic layers of aquatic sediments, where the respective reactions and ecophysiologies are compressed into fractions of centimeters; and (ii) the same ecosystem function, but distributed over depths of tens of meters in the oxygen minimum zones (OMZs) of the global ocean. The chapter focuses on the results obtained using slurries of homogenized sediment, and then focuses on the data derived with intact sediment cores, and, finally, draw comparisons between the two at the end, without dwelling too long on the respective complexities of each method. Anammox bacteria appear active in both low-oxygen and suboxic waters, and such conditions are often considered as prerequisites for denitrification, since oxygen represses synthesis and activity of denitrifying enzymes, though the effect may be more subtle.
Key Concept Ranking
- Anaerobic Ammonium Oxidation
Schematic representation of the oxic and suboxic zones in sediments and OMZs to highlight the respective difference in depth scale (a, b) and representative examples for sediment in the Cascadia Basin (c) and the central Arabian Sea (d) (panels c and d are reproduced, respectively, from Engström et al.  and Nicholls et al.  , Copyright by the American Society of Limnology and Oceanography, Inc.). Note the high NO3 – (typical estuarine or deep sea) and low NO3 – (coastal or shelf sea) depicted in panel a.
Simplified representation of the N cycle highlighting the key characteristic of the anammox reaction. Nitrate reduction refers to the one-step reduction of NO3 – to NO2 – and complete denitrification would ultimately generate N2 gas; assimilatory reduction of NO3 – to organic N has been omitted. (Reproduced and amended from Trimmer et al. [2003 ] with permission from The American Society for Microbiology.)
Contribution from anammox to the production of N2 (ra %) measured in slurries of anoxic sediment. (a) Relatively simple linear relationship for water depths up to 150 m with the correlation coefficient (r). (b) Complete data set against water depth on a common log scale. The open circle is the mean for ra at this site (S9 the deep Skagerrak) (see Table 1 ).
Composite of all available anammox- and denitrification-specific activity slurry data (rate) as a function of water depth. Rate data have been log transformed (log10+1) and plotted against water depth on a common log scale. Data are from Table 1 ; note the difference in both the range and variance associated with the measures of denitrification.
A composite of all available anammox-specific activity slurry data (rate) as a function of denitrification. The data are split between coastal and shelf waters deeper than 20 m and estuarine and coastal waters shallower than 20 m. Data have been normalized by common log transformation (log10+1) and are from Table 1 .
The yield of 29N2 from the oxidation of 15NH4 + in the presence of either just 14NO3 – or just NO2 – or a dual labeling experiment with 100 µmol of NO3 – liter–1 and increasing NO2 –. Clearly, the availability of NO2 – and NO3 – affects the significance of anammox. Data are from Trimmer et al. (2005) . Sediment is from Grays in the Thames estuary.
Decreasing sediment metabolism as a function of water depth for both oxygen uptake and total N2 production. Note the inverted triangles for the data from Sagami Bay ( Glud et al., 2009 ), which have been omitted from the nonlinear regression. The data are plotted on a double common log scale, and the coefficients were derived using a simple power function. Data are from Table 2 .
Relationships between N2 metabolisms and total sediment metabolism. (a) Total N2 production scattered against oxygen uptake. (b) Anammox against denitrification. Data have been normalized by common log transformation (log10+1), and the correlation coefficient (r) is given in each panel. In a, the open triangles mark the approximate range of data reported by Seitzinger and Giblin (1996) . The inset gives the relationship through the original linear data, where the slope (b 1) is equivalent to the ratio (as b 0 = 0) and ratio is equivalent to the pairwise comparison given in the text.
Scatter plot of anammox as a function of denitrification to illustrate the bias toward denitrification in the sediment slurries in shallower water. Units for the intact sediment core data are µmol of N m–2 h–1 (as in Fig. 8 b) and for the slurries are nmol of N cm–3 h–1 (as in Fig. 5 ). Data have been normalized by common log transformation (log10+1), and the correlation coefficient (r) is given in each case.
Patterns of dissolved inorganic N species and oxygen within OMZs, made up from the available anammox database (see Table 3 ). (a, b) Nitrite and ammonium each as a function of oxygen, respectively. (c) Nitrite as a function of nitrate; the label for the nitrate axis in panel c is given as the primary axis in panel d. (d) Ammonium as a function of nitrite, with nitrite on the secondary axis.
Anammox activity measured by enrichment with 15NH4 + as a function of the concentration of ambient nitrite, made up from the available anammox database (see Table 3 .). To illustrate the overall trend, two outliers have been removed that had activity of 170 and 270 nmol of N2 liter–1 day–1.
Anammox activity measured by enrichment with 15NH4 + as a function of the concentration of ambient ammonium, made up from the available anammox database (see Table 3 .).
Published and unpublished rates of anammox and denitrification measured in anoxic homogenized or slurrified sediment a
Published and unpublished rates of sedimentary oxygen uptake and anammox and denitrification measured in intact sediment cores a
Published anammox and denitrification rates measured with 15N-stable isotopes in water column OMZs a