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Viable cyanobacteria in the deep continental subsurface.

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PubMed ID: 30275328

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Puente-Sánchez F, Arce-Rodríguez A, Oggerin M, García-Villadangos M, Moreno-Paz M, Blanco Y, Rodríguez N, Bird L, Lincoln SA, Tornos F, Prieto-Ballesteros O, Freeman KH, Pieper DH, Timmis KN, Amils R, Parro V

Proc Natl Acad Sci U S A. Oct 2018. doi: 10.1073/pnas.1808176115

COMMENT: In this work, after analyzing samples from the Iberian Pyrite Belt Mars analog (southwestern Spain), the authors present molecular, microscopic, and metagenomic evidences that support the cyanobacterial predominance in deep subsurface rocks. The authors show that, even without sunlight, cyanobacteria are able to live down to the deep terrestrial biosphere. The detected cyanobacteria were related to surface rock-dwelling lineages that have a high tolerance to environmental and nutritional stress.

Using NGS technologies they target 16S V5-V6 regions with the primers 807F and 1050R  and sequence using 250-bp paired-end reads on a Illumina MiSeq platform for taxonomic profiling of the samples. They also use the approach of shotgun metagenomics at low coverage for analyzing a potential nonphotosynthetic hydrogen-based lithoautotrophic cyanobacterial metabolism with the hypothesis of hydrogen as an electron donor for these cyanobacteria.

The authors conclude:

Our proposal of cyanobacterial hydrogenotrophy is consistent with a large body of literature, as well as several parallel lines of evidence presented in this work.While the dark metabolism of cyanobacteria is still a matter of ongoing research, their unequivocal presence in samples from this and other studies calls for a reevaluation of their potential roles in deep subsurface ecosystems and increases their relevance in early life and astrobiological scenarios.

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Raquel Tobes