Diversity of key genes for carbon and nitrogen fixation in soils from the Sør Rondane Mountains, East Antarctica
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Although Cyanobacteria are generally considered the most important primary producers and diazotrophs in Antarctic terrestrial ecosystems, in several high-altitude Antarctic regions, they were previously reported to be relatively rare in some samples. In view of these observations, we investigated the presence of non-cyanobacterial carbon- and nitrogen-fixing microorganisms in oligotrophic exposed soils without visible cyanobacterial biomass from the Sør Rondane Mountains, East Antarctica. An Illumina amplicon sequencing approach was used to analyze the bacterial community composition and the diversity and abundance of key genes involved in the carbon- and nitrogen-fixation processes. Analysis of the large subunit of type I ribulose-1,5-biphosphate carboxylase/oxygenase genes (cbbL) revealed a large actinobacterial, and alpha-, beta-, and gammaproteobacterial diversity of CbbL type IC, whereas type IA diversity was restricted to Bradyrhizobium sp.-like sequences. Although a large portion of the CbbL sequences grouped with those of cultivated bacteria, some belonged to currently unknown phylotypes. Data of 16S rRNA genes, however, also revealed that samples contained either considerable numbers of Cyanobacteria or Trebouxiophyceae as oxygenic phototrophic primary producers. Dinitrogenase-reductase genes (nifH) most similar to those of Nostocales cyanobacteria were dominantly retrieved from these oligotrophic soils. These findings suggest that diverse microorganisms capable of assimilating carbon dioxide through the Calvin–Benson–Bassham cycle inhabit these extreme terrestrial systems and potentially may contribute to primary production. However, Cyanobacteria, present in greatly varying numbers as assessed by Illumina amplicon sequencing of a 16S rRNA gene fragment, appear to be the most important nitrogen fixers in these habitats.
KeywordsRuBisCO Diazotrophy Sequencing Autotrophy Community analysis Antarctic
Operational nitrogenase unit
Operational RuBisCO unit
Operational taxonomic unit
This work was supported by the Fund for Scientific Research—Flanders (Project G.0146.12). Additional support was provided by the Belgian Science Policy Office (Project CCAMBIO). The computational resources (Stevin Supercomputer Infrastructure) and services used in this work were provided by the Flemish Supercomputer Center (VSC) funded by Ghent University, the Hercules Foundation, and the Flemish Government—department EWI. This work is a contribution to the State of the Antarctic Ecosystem (AntEco) research program of the Scientific Committee on Antarctic Research (SCAR).
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Conflict of interest
The authors declare there is no conflict of interest.
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