Articles | Volume 13, issue 21
https://doi.org/10.5194/bg-13-6031-2016
https://doi.org/10.5194/bg-13-6031-2016
Research article
 | 
03 Nov 2016
Research article |  | 03 Nov 2016

Microbial communities and their predicted metabolic characteristics in deep fracture groundwaters of the crystalline bedrock at Olkiluoto, Finland

Malin Bomberg, Tiina Lamminmäki, and Merja Itävaara

Abstract. The microbial diversity in oligotrophic isolated crystalline Fennoscandian Shield bedrock fracture groundwaters is high, but the core community has not been identified. Here we characterized the bacterial and archaeal communities in 12 water conductive fractures situated at depths between 296 and 798 m by high throughput amplicon sequencing using the Illumina HiSeq platform. Between 1.7  ×  104 and 1.2  ×  106 bacterial or archaeal sequence reads per sample were obtained. These sequences revealed that up to 95 and 99 % of the bacterial and archaeal sequences obtained from the 12 samples, respectively, belonged to only a few common species, i.e. the core microbiome. However, the remaining rare microbiome contained over 3- and 6-fold more bacterial and archaeal taxa. The metabolic properties of the microbial communities were predicted using PICRUSt. The approximate estimation showed that the metabolic pathways commonly included fermentation, fatty acid oxidation, glycolysis/gluconeogenesis, oxidative phosphorylation, and methanogenesis/anaerobic methane oxidation, but carbon fixation through the Calvin cycle, reductive TCA cycle, and the Wood–Ljungdahl pathway was also predicted. The rare microbiome is an unlimited source of genomic functionality in all ecosystems. It may consist of remnants of microbial communities prevailing in earlier environmental conditions, but could also be induced again if changes in their living conditions occur.

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Short summary
Over 95 % of the microbial communities in isolated groundwater in Olkiluoto bedrock, Finland, is composed of only a few common species. The remaining rare microbiome contains over 3- and 6-fold more microbial diversity. The rare microbiome is an unlimited source of genomic functionality in the ecosystem. These microorganisms can respond to change caused by physical or biological factors that may lead to alterations in the diversity and function of the microbial communities in crystalline bedrock.
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