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Diazotroph Diversity in the Sea Ice, Melt Ponds, and Surface Waters of the Eurasian Basin of the Central Arctic Ocean

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ABSTRACT

The Eurasian basin of the Central Arctic Ocean is nitrogen limited, but little is known about the presence and role of nitrogen-fixing bacteria. Recent studies have indicated the occurrence of diazotrophs in Arctic coastal waters potentially of riverine origin. Here, we investigated the presence of diazotrophs in ice and surface waters of the Central Arctic Ocean in the summer of 2012. We identified diverse communities of putative diazotrophs through targeted analysis of the nifH gene, which encodes the iron protein of the nitrogenase enzyme. We amplified 529 nifH sequences from 26 samples of Arctic melt ponds, sea ice and surface waters. These sequences resolved into 43 clusters at 92% amino acid sequence identity, most of which were non-cyanobacterial phylotypes from sea ice and water samples. One cyanobacterial phylotype related to Nodularia sp. was retrieved from sea ice, suggesting that this important functional group is rare in the Central Arctic Ocean. The diazotrophic community in sea-ice environments appear distinct from other cold-adapted diazotrophic communities, such as those present in the coastal Canadian Arctic, the Arctic tundra and glacial Antarctic lakes. Molecular fingerprinting of nifH and the intergenic spacer region of the rRNA operon revealed differences between the communities from river-influenced Laptev Sea waters and those from ice-related environments pointing toward a marine origin for sea-ice diazotrophs. Our results provide the first record of diazotrophs in the Central Arctic and suggest that microbial nitrogen fixation may occur north of 77°N. To assess the significance of nitrogen fixation for the nitrogen budget of the Arctic Ocean and to identify the active nitrogen fixers, further biogeochemical and molecular biological studies are needed.

No MeSH data available.


Relative abundances of different nifH subclusters in Central Arctic environments. The number of sequences retrieved from each environment is shown in parenthesis. Open waters correspond to the region close to the Laptev Sea.
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Figure 2: Relative abundances of different nifH subclusters in Central Arctic environments. The number of sequences retrieved from each environment is shown in parenthesis. Open waters correspond to the region close to the Laptev Sea.

Mentions: During our study in summer 2012, nifH gene fragments were amplified from 26 of the 53 samples collected in different Arctic environments: sea ice, melt ponds and surface water column (Figure 1). A total of 529 sequences were retrieved, 40% of them from the upper part of the sea ice and only 5% from melt ponds (Table 1; Supplementary Table S1). These sequences were clustered into 43 clusters at 92% amino acid similarity and were distributed across all four main nifH clusters I–IV as defined by Zehr et al. (2003), including both cyanobacterial and non-cyanobacterial phylotypes (Figures 2 and 3). Central Arctic sequences affiliated with Cluster I contained mainly Proteobacteria (1G and 1K), Firmicutes (1E), Cyanobacteria (1B) and several uncultivated microorganisms. Cluster II contained Proteobacteria (2C), Firmicutes (2A), and members of the Archaea (2B). Cluster III contained putative anaerobes including sulfate reducing genera of the Deltaproteobacteria, and genera such as Clostridium. Cluster IV contained nifH paralogs that are thought to function in metabolic processes other than nitrogen fixation (e.g., Young, 2005; Staples et al., 2007).


Diazotroph Diversity in the Sea Ice, Melt Ponds, and Surface Waters of the Eurasian Basin of the Central Arctic Ocean
Relative abundances of different nifH subclusters in Central Arctic environments. The number of sequences retrieved from each environment is shown in parenthesis. Open waters correspond to the region close to the Laptev Sea.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5120112&req=5

Figure 2: Relative abundances of different nifH subclusters in Central Arctic environments. The number of sequences retrieved from each environment is shown in parenthesis. Open waters correspond to the region close to the Laptev Sea.
Mentions: During our study in summer 2012, nifH gene fragments were amplified from 26 of the 53 samples collected in different Arctic environments: sea ice, melt ponds and surface water column (Figure 1). A total of 529 sequences were retrieved, 40% of them from the upper part of the sea ice and only 5% from melt ponds (Table 1; Supplementary Table S1). These sequences were clustered into 43 clusters at 92% amino acid similarity and were distributed across all four main nifH clusters I–IV as defined by Zehr et al. (2003), including both cyanobacterial and non-cyanobacterial phylotypes (Figures 2 and 3). Central Arctic sequences affiliated with Cluster I contained mainly Proteobacteria (1G and 1K), Firmicutes (1E), Cyanobacteria (1B) and several uncultivated microorganisms. Cluster II contained Proteobacteria (2C), Firmicutes (2A), and members of the Archaea (2B). Cluster III contained putative anaerobes including sulfate reducing genera of the Deltaproteobacteria, and genera such as Clostridium. Cluster IV contained nifH paralogs that are thought to function in metabolic processes other than nitrogen fixation (e.g., Young, 2005; Staples et al., 2007).

View Article: PubMed Central - PubMed

ABSTRACT

The Eurasian basin of the Central Arctic Ocean is nitrogen limited, but little is known about the presence and role of nitrogen-fixing bacteria. Recent studies have indicated the occurrence of diazotrophs in Arctic coastal waters potentially of riverine origin. Here, we investigated the presence of diazotrophs in ice and surface waters of the Central Arctic Ocean in the summer of 2012. We identified diverse communities of putative diazotrophs through targeted analysis of the nifH gene, which encodes the iron protein of the nitrogenase enzyme. We amplified 529 nifH sequences from 26 samples of Arctic melt ponds, sea ice and surface waters. These sequences resolved into 43 clusters at 92% amino acid sequence identity, most of which were non-cyanobacterial phylotypes from sea ice and water samples. One cyanobacterial phylotype related to Nodularia sp. was retrieved from sea ice, suggesting that this important functional group is rare in the Central Arctic Ocean. The diazotrophic community in sea-ice environments appear distinct from other cold-adapted diazotrophic communities, such as those present in the coastal Canadian Arctic, the Arctic tundra and glacial Antarctic lakes. Molecular fingerprinting of nifH and the intergenic spacer region of the rRNA operon revealed differences between the communities from river-influenced Laptev Sea waters and those from ice-related environments pointing toward a marine origin for sea-ice diazotrophs. Our results provide the first record of diazotrophs in the Central Arctic and suggest that microbial nitrogen fixation may occur north of 77°N. To assess the significance of nitrogen fixation for the nitrogen budget of the Arctic Ocean and to identify the active nitrogen fixers, further biogeochemical and molecular biological studies are needed.

No MeSH data available.