Diversity of CBBL, NIFH and PUFLM genes in soils around the Princess Elisabeth station, Sør Rondane Mountains, Antarctica

Introduction: In Antarctica, the presence of native flowering plants is restricted to the Peninsula. In continental Antarctica, photosynthesis by Cyanobacteria is generally thought to be the main primary source of organic carbon. Many cyanobacterial species are also capable of fixing nitrogen, allowing them to survive and prosper in almost every environment, including the adverse conditions of Antarctica. Several studies, including our own findings, however, have shown that Cyanobacteria are sometimes only scarcely present in the terrestrial Antarctic microbial communities. Furthermore, both carbon and nitrogen fixation require a considerable amount of ATP. In Antarctica, sunlight – an abundant energy source during the Antarctic summer – may represent an important resource to generate this ATP. Some bacteria, for example, are known to use rhodopsin-like pigments to exploit sunlight, whereas aerobic anoxygenic photosynthetic bacteria can use bacteriochlorophyll to harvest light energy that is then stored as ATP. We explored the hypothesis that, in the ice-free regions of continental Antarctica, other primary producers and bacteria that exploit solar energy may contribute to carbon and nitrogen fixation, in addition to Cyanobacteria. Methods & Materials: The presence and diversity of non-cyanobacterial prokaryotes that possess these properties was studied in four terrestrial samples gathered in the vicinity of the Belgian Princess Elisabeth Station (Sør Rondane Mountains, Queen Maud Land, East Antarctica). A culture independent approach by Illumina MiSeq amplicon sequencing of cbbL (carbon fixation, RuBisCO type I), nifH (nitrogen fixation), and pufLM and proteorhodopsin genes (light-harvesting) was used. After curation, sequences were placed in phylogenies with existing sequence data to reveal phylogenetic affiliations. Results: Proteorhodopsin genes failed to amplify from all tested samples. Illumina sequencing extended the functional genes’ sequence datasets, previously obtained by performing PCR clone libraries, by several orders of magnitude. The clone library rarefaction analysis showed that no saturation was reached for any gene, indicating that a large proportion of the diversity remains unknown using this approach. Illumina results, also revealing the diversity obtained with clone library analysis, additionally uncovers part of the previously unknown diversity, thus improving our knowledge in the diversity of the functional genes. Discussion: Overall, the data obtained with Illumina suggest that, in soils in the proximity of the Belgian Princess Elisabeth Station in the Sør Rondane Mountains, a broad and unknown diversity of bacteria harboring cbbL, nifH and pufLM genes are present. Non-cyanobacterial cbbL genes were dominant to cyanobacterial ones, indicating that their hosts may contribute significantly to the input of organic matter in the oligotrophic Antarctic biosphere. Diversity of nifH was low, as mostly Cyanobacteria affiliated sequences were recovered from the sequencing data, suggesting that, although they may only be present in small numbers, diazotrophic Cyanobacteria supply most of the fixed nitrogen in Antarctic soils. Furthermore, aerobic anoxygenic phototrophic bacteria were shown to be present in Antarctic soils. Photoheterotrophy, using the abundant sunlight of the Antarctic summer, may thus indeed be a useful life strategy in this challenging environment