Abstract
The composition and metabolic functions of prokaryotic communities in the western subarctic Pacific (WSP), where strong mixing of waters from the Sea of Okhotsk and the East Kamchatka Current result in transfer to the Oyashio Current, were investigated using a shotgun metagenome sequencing approach. Functional metabolic genes related to nutrient cycling of nitrogen, sulfur, carbohydrates, iron and amino acids were differently distributed between the surface and deep waters of the WSP. Genes related to nitrogen metabolism were mainly found in deep waters, where Thaumarchaeaota, Sphingomonadales, and Pseudomonadales were closely associated and performing important roles in ammonia oxidation, assimilatory nitrate reduction, and dissimilatory nitrate reduction processes, respectively. In addition, orders affiliated to Spingobacteria and Alphaproteobacteria were crucial for sulfate reduction and abundant at 3000 m, whereas orders affiliated to Gammaproteobacteria, which harbored the most sulfate reduction genes, were abundant at 1000 m. Additionally, when compared with the East Kamchatka Current, the prokaryotes in the Oyashio Current were likely to consume more energy for synthesizing cellular components. Also, genes encoding iron transport and siderophore biosynthesis proteins were in low abundance, indicating that the iron was not a limiting factor in the Oyashio current. In contrast, in the East Kamchatka Current, prokaryotes were more likely to directly utilize the amino acids and absorb iron from the environment. Overall, our data indicated that the transformation from the East Kamchatka Current to the Oyashio Current reshapes not only the composition of microbial community, but also the function of the metabolic processes. These results extended our knowledge of the microbial composition and potential metabolism in the WSP.
Highlights
Microbes in marine ecosystems are the most important drivers of biogeochemical cycling on a global scale (Azam et al, 1983), since they are responsible for the re-mineralization of organic matter and the transfer of both nutrients and energy to the higher trophic levels in the ocean (Nealson, 1997; Mason et al, 2009)
When compared to the ammoniaoxidizing microorganisms in the North Pacific Subtropical Gyre, the ammonia monooxygenase was mainly harbored by Archaea (Thaumarchaeota) in the western subarctic Pacific (WSP) instead of bacteria
The products of ammonia oxidation from Thaumarchaeota could be further processed by Sphingomonadales and Pseudomonadales in the WSP, evidenced by their positive relationship with Thaumarchaeota, and for carrying dissimilatory nitrate reductase and nitrite reductase
Summary
Microbes in marine ecosystems are the most important drivers of biogeochemical cycling on a global scale (Azam et al, 1983), since they are responsible for the re-mineralization of organic matter and the transfer of both nutrients and energy to the higher trophic levels in the ocean (Nealson, 1997; Mason et al, 2009). The metagenomics approach has previously been applied to investigate the diversity and abundance of genes associated with nitrogen, sulfur, carbon and phosphorous metabolism, in bodies of water such as the vertical water column in the North Pacific Subtropical Gyre (DeLong et al, 2006), the central Pacific Ocean (Hewson et al, 2009), the California Current (Allen et al, 2012), the Dead Sea (Bodaker et al, 2010), the Mediterranean deepsea brines (Smedile et al, 2013), the Mariana Trench (Nunoura et al, 2015) and the southwestern Atlantic Ocean (Junior et al, 2015). Until now, a general lack of genomic information in the western subarctic Pacific (WSP) Ocean has hindered our understanding of the adaptation of microbes to the subarctic environment with near-freezing temperatures and diverse marine geography
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