Viable cyanobacteria in the deep continental subsurface

Cyanobacteria are ecologically versatile microorganisms inhabiting most environments, ranging from marine systems to arid deserts. Although they possess several pathways for light-independent energy generation, until now their ecological range appeared to be restricted to environments with at least occasional exposure to sunlight. Here we present molecular, microscopic, and metagenomic evidence that cyanobacteria predominate in deep subsurface rock samples from the Iberian Pyrite Belt Mars analog (southwestern Spain). Metagenomics showed the potential for a hydrogen-based lithoautotrophic cyanobacterial metabolism. Collectively, our results suggest that they may play an important role as primary producers within the deep-Earth biosphere. Our description of this previously unknown ecological niche for cyanobacteria paves the way for models on their origin and evolution, as well as on their potential presence in current or primitive biospheres in other planetary bodies, and on the extant, primitive, and putative extraterrestrial biospheres.
This work was supported by the European Research Council Advanced Grant ERC250350-IPBSL, and the Spanish Ministerio de Economía y Competitividad/Fondo Europeo de Desarrollo Regional Grants AYA2011-24803 and ESP2015-69540-R. F.P.-S. is currently funded by the Spanish Ministerio de Economía y Competitividad/Fondo Europeo de Desarrollo Regional Grant CTM2016-80095-C2-1-R.