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

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.


Related in: MedlinePlus

Dissimilarities between different oceanic regions based on their nifH phylogenetic signature. Plot of the first two principal coordinate axes of the Principal coordinates analysis (PCoA) derived from the Unifrac distances between different oceanic regions included in the maximum likelihood tree (Figure 6). The further away the samples are, the more dissimilar they are in terms of nifH phylogenetic signature. An automatic correction for negative eigenvalues was used. A cluster dendrogram is superimposed. The lines indicate the strength of the dissimilarity. Oceanic regions connected with a solid line have a dissimilarity less than 0.69 (Supplementary Table S2). The dashed line indicates a dissimilarity of 0.76 and the doted line between the Central Arctic and the subtropical Atlantic indicates the maximum dissimilarity of 0.85 (Supplementary Table S2). The number of representative sequences (97% nucleotide identity) from each oceanic region included in the analysis is indicated next to the region’s name.
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC5120112&req=5

Figure 7: Dissimilarities between different oceanic regions based on their nifH phylogenetic signature. Plot of the first two principal coordinate axes of the Principal coordinates analysis (PCoA) derived from the Unifrac distances between different oceanic regions included in the maximum likelihood tree (Figure 6). The further away the samples are, the more dissimilar they are in terms of nifH phylogenetic signature. An automatic correction for negative eigenvalues was used. A cluster dendrogram is superimposed. The lines indicate the strength of the dissimilarity. Oceanic regions connected with a solid line have a dissimilarity less than 0.69 (Supplementary Table S2). The dashed line indicates a dissimilarity of 0.76 and the doted line between the Central Arctic and the subtropical Atlantic indicates the maximum dissimilarity of 0.85 (Supplementary Table S2). The number of representative sequences (97% nucleotide identity) from each oceanic region included in the analysis is indicated next to the region’s name.

Mentions: The diazotrophic community of the Central Arctic is highly dissimilar to all other regions and environments we compared it to as unweighted unifrac distances were the highest (0.85–0.78), when the other regions were between (0.75–0.58) (Supplementary Table S2). At 97% nucleotide identity almost no sequences from different oceanic regions clustered together (Figure 6). Only five phylotypes were shared between the North Atlantic and the Subtropical Atlantic (Figure 6). The nifH diversity in sea ice, melt ponds and surface waters of the Central Arctic is different from the coastal Canadian Arctic marine diazotrophic community (Mackenzie river, Baffin bay) (Figure 7). Furthermore, it also differs from the sea ice, snow and water column communities from the coastal Eurasian Arctic (close to Svalbard) (Figure 7). The rarefaction curves show that the diversity in regions from which we acquired a greater number of sequences (i.e., the Central Arctic, the North Atlantic and the Subtropical Atlantic) appears to have been reasonably well sampled (Supplementary Figure S4B). However, the other oceanic regions are still in the rapid accumulation phase of their respective curves and deeper sequencing is likely to strongly affect their diversity profiles (Supplementary Figure S4B). We therefore place more interpretive weight on dissimilarities between our well-sampled regions (marked in the dissimilarities Supplementary Table S2), while noting that dissimilarities bearing on the Arctic tundra, Canadian Arctic, Eurasian Basin and Antarctic might be subject to change when the sampling effort is increased.


Diazotroph Diversity in the Sea Ice, Melt Ponds, and Surface Waters of the Eurasian Basin of the Central Arctic Ocean
Dissimilarities between different oceanic regions based on their nifH phylogenetic signature. Plot of the first two principal coordinate axes of the Principal coordinates analysis (PCoA) derived from the Unifrac distances between different oceanic regions included in the maximum likelihood tree (Figure 6). The further away the samples are, the more dissimilar they are in terms of nifH phylogenetic signature. An automatic correction for negative eigenvalues was used. A cluster dendrogram is superimposed. The lines indicate the strength of the dissimilarity. Oceanic regions connected with a solid line have a dissimilarity less than 0.69 (Supplementary Table S2). The dashed line indicates a dissimilarity of 0.76 and the doted line between the Central Arctic and the subtropical Atlantic indicates the maximum dissimilarity of 0.85 (Supplementary Table S2). The number of representative sequences (97% nucleotide identity) from each oceanic region included in the analysis is indicated next to the region’s name.
© Copyright Policy
Related In: Results  -  Collection

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

Figure 7: Dissimilarities between different oceanic regions based on their nifH phylogenetic signature. Plot of the first two principal coordinate axes of the Principal coordinates analysis (PCoA) derived from the Unifrac distances between different oceanic regions included in the maximum likelihood tree (Figure 6). The further away the samples are, the more dissimilar they are in terms of nifH phylogenetic signature. An automatic correction for negative eigenvalues was used. A cluster dendrogram is superimposed. The lines indicate the strength of the dissimilarity. Oceanic regions connected with a solid line have a dissimilarity less than 0.69 (Supplementary Table S2). The dashed line indicates a dissimilarity of 0.76 and the doted line between the Central Arctic and the subtropical Atlantic indicates the maximum dissimilarity of 0.85 (Supplementary Table S2). The number of representative sequences (97% nucleotide identity) from each oceanic region included in the analysis is indicated next to the region’s name.
Mentions: The diazotrophic community of the Central Arctic is highly dissimilar to all other regions and environments we compared it to as unweighted unifrac distances were the highest (0.85–0.78), when the other regions were between (0.75–0.58) (Supplementary Table S2). At 97% nucleotide identity almost no sequences from different oceanic regions clustered together (Figure 6). Only five phylotypes were shared between the North Atlantic and the Subtropical Atlantic (Figure 6). The nifH diversity in sea ice, melt ponds and surface waters of the Central Arctic is different from the coastal Canadian Arctic marine diazotrophic community (Mackenzie river, Baffin bay) (Figure 7). Furthermore, it also differs from the sea ice, snow and water column communities from the coastal Eurasian Arctic (close to Svalbard) (Figure 7). The rarefaction curves show that the diversity in regions from which we acquired a greater number of sequences (i.e., the Central Arctic, the North Atlantic and the Subtropical Atlantic) appears to have been reasonably well sampled (Supplementary Figure S4B). However, the other oceanic regions are still in the rapid accumulation phase of their respective curves and deeper sequencing is likely to strongly affect their diversity profiles (Supplementary Figure S4B). We therefore place more interpretive weight on dissimilarities between our well-sampled regions (marked in the dissimilarities Supplementary Table S2), while noting that dissimilarities bearing on the Arctic tundra, Canadian Arctic, Eurasian Basin and Antarctic might be subject to change when the sampling effort is increased.

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.


Related in: MedlinePlus