Abundance, diversity, and activity of ammonia-oxidizing prokaryotes in the coastal arctic ocean in summer and winter
Date
2009
Authors
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Journal ISSN
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Publisher
University of Delaware
Abstract
Ammonia oxidation, the first step in nitrification, is performed by certain Betaand
Gammaproteobacteria and mesophilic Crenarchaea to generate metabolic energy.
Ammonia monooxygenase (amoA) genes from both Bacteria and Crenarchaea have
been found in a variety of marine ecosystems, but the relative importance of Bacteria
versus Crenarchaea in ammonia oxidation is unresolved, and seasonal comparisons are
rare. In this study, we compare the abundance of betaproteobacterial and crenarchaeal
amoA genes in the coastal Artic Ocean during summer and winter seasons over two
years. Betaproteobacterial and crenarchaeal amoA genes were present in both seasons,
but were more abundant during the winter. Archaeal amoA genes were more abundant
than betaproteobacterial amoA genes in the first year, but betaproteobacterial amoA
was more abundant than archaeal amoA the following year. Summer and winter
betaproteobacterial amoA clone libraries were significantly different. Gene sequences
of amoA were similar to those found in temperate and polar environments. The ratio
of archaeal amoA gene copies to Marine Group I crenarchaeal 16S rRNA genes
averaged 2.9 over both seasons, implying that ammonia oxidation was common in
Crenarchaea at this location. Nitrification rates were highest in the winter when
ammonia oxidizer abundance was greatest, suggesting that ammonia oxidation plays an important role in coastal arctic waters during the winter when the ocean is ice
covered and photosynthesis is at a minimum.