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Genomic and metatranscriptomic analyses of carbon remineralization in an Antarctic polynya.

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PubMed ID: 30786927

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Kim SJ, Kim JG, Lee SH, Park SJ, Gwak JH, Jung MY, Chung WH, Yang EJ, Park J, Jung J, Hahn Y, Cho JC, Madsen EL, Rodriguez-Valera F, Hyun JH, Rhee SK

Microbiome. 02 2019. doi: 10.1186/s40168-019-0643-4

COMMENT: This work describes a characterization of the bacterial composition at the Southern Ocean polynya. Researchers analyze bacterial populations both at the genomic and metatranscriptomic level, and get more knowledge about the metabolic potential of these key ecological environments.

Polynya are spaces of water that remain in liquid state in the Arctic and Antarctic regions despite being surrounded by sea ice. These places are ecologically relevant, since they are regions of intense primary production through carbon fixation by phytoplankton.

Microbial blooms, mainly due to the red algae Phaeocystis antarctica, occur mainly during light availability periods (summer at either the North or the South Poles). These blooms make polynya work as biological pumps, transferring carbon fixed by phytoplankton to higher trophic levels and then exporting it to the deep ocean. In contrast, in Amundsen Sea polynya, the fixed carbon is recycled and mineralized via microbial loop and does not leave the polynya, probably due to heterotrophic bacteria activity, which could be favored by global warming. Understanding the bacterial composition and the metabolic activity of these polynya during microbial bloom periods could be key to quantify global warming impact.

This work has performed a comparative analysis of samples from different phases of microbial bloom at Amundsen Sea polynya, and from sea ice-covered ocean.The methodology included metagenome sequencing, assembly and annotation from samples in peak and decline phytoplankton activity phases, along with geochemical analysis to know the concentration of inorganic nutrients and photosynthetic potential (Chl-a concentration).

The genome reconstruction provides relevant information about the major taxa responsible for the utilization of the organic matter in the polynya, revealing that the dominant heterotrophic bacteria responsible for this biological activity belong to Bacteroidetes and Gammaproteobacteria. 

The metabolic potential of dominant bacterial clades of Bacteroidetes and Gammaproteobacteria can be used to predict temporal community succession linked to the availability of substrates derived from phases of the P. antarctica bloom. 

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Vicente Díaz