Microbial metagenomes from three aquifers in the Fennoscandian shield terrestrial deep biosphere reveal metabolic partitioning among populations

• Published in: The ISME Journal
• Main Authors: Wu, Xiaofen, Holmfeldt, Karin, Hubalek, Valerie, Lundin, Daniel, Åström, Mats, Bertilsson, Stefan, Dopson, Mark
• Format: Text
• Language: English
• Published: Nature Publishing Group 2016
• Subjects: Original Article; Fennoscandian
• Online Access: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5029217/; http://www.ncbi.nlm.nih.gov/pubmed/26484735; https://doi.org/10.1038/ismej.2015.185

Microorganisms in the terrestrial deep biosphere host up to 20% of the earth's biomass and are suggested to be sustained by the gases hydrogen and carbon dioxide. A metagenome analysis of three deep subsurface water types of contrasting age (from <20 to several thousand years) and depth (171 to 448 m) revealed phylogenetically distinct microbial community subsets that either passed or were retained by a 0.22 μm filter. Such cells of <0.22 μm would have been overlooked in previous studies relying on membrane capture. Metagenomes from the three water types were used for reconstruction of 69 distinct microbial genomes, each with >86% coverage. The populations were dominated by Proteobacteria, Candidate divisions, unclassified archaea and unclassified bacteria. The estimated genome sizes of the <0.22 μm populations were generally smaller than their phylogenetically closest relatives, suggesting that small dimensions along with a reduced genome size may be adaptations to oligotrophy. Shallow ‘modern marine' water showed community members with a predominantly heterotrophic lifestyle. In contrast, the deeper, ‘old saline' water adhered more closely to the current paradigm of a hydrogen-driven deep biosphere. The data were finally used to create a combined metabolic model of the deep terrestrial biosphere microbial community.