Abundance, diversity, and activity of ammonia-oxidizing prokaryotes in the coastal arctic ocean in summer and winter

Christman, Glenn
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University of Delaware
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.