Microbial co-occurrence patterns in deep Precambrian bedrock fracture fluids

Abstract

The bacterial and archaeal community composition and the possible carbon assimilation processes and energy sources of microbial communities in oligotrophic, deep, crystalline bedrock fractures is yet to be resolved. In this study, intrinsic microbial communities from groundwater of six fracture zones from 180 to 2300 m depths in Outokumpu bedrock were characterized using high-throughput amplicon sequencing and metagenomic prediction. Comamonadaceae-, Anaerobrancaceaeand Pseudomonadaceae-related operational taxonomic units (OTUs) form the core community in deep crystalline bedrock fractures in Outokumpu. Archaeal communities were mainly composed of Methanobacteriaceae-affiliating OTUs. The predicted bacterial metagenomes showed that pathways involved in fatty acid and amino sugar metabolism were common. In addition, relative abundance of genes coding the enzymes of autotrophic carbon fixation pathways in predicted metagenomes was low. This indicates that heterotrophic carbon assimilation is more important for microbial communities of the fracture zones. Network analysis based on cooccurrence of OTUs revealed possible "keystone" genera of the microbial communities belonging to Burkholderiales and Clostridiales. Bacterial communities in fractures resemble those found in oligotrophic, hydrogen-enriched environments. Serpentinization reactions of ophiolitic rocks in Outokumpu assemblage may provide a source of energy and organic carbon compounds for the microbial communities in the fractures. Sulfate reducers and methanogens form a minority of the total microbial communities, but OTUs forming these minor groups are similar to those found in other deep Precambrian terrestrial bedrock environments.

Reactivation of Deep Subsurface Microbial Community in Response to Methane or Methanol Amendment

“…In addition, marker genes for methanogenesis have been previously detected throughout the drillhole water column (Nyyssönen et al, 2014; Purkamo et al, 2016). …”

Geological gas‐storage shapes deep life

“…Ad hoc studies have been carried out on the microbial ecology of gas storage aquifers in France for almost two decades (Basso et al ., ; Berlendis et al ., ; Aüllo et al ., ; Ranchou‐Peyruse et al ., ). While various microbial metabolisms have been highlighted in these ecosystems, some seem to play key roles in the functioning of the microbial communities, particularly sulfate‐reducing microorganisms (SRM) and methanogenic archaea, as already demonstrated for other subsurface environments (Itävaara et al ., ; Schrenk et al ., ; Purkamo et al ., ). Moreover, one of these studies targeting French gas storage aquifers suggested that CO 2 and H 2 could be the source of the functioning of the microbial communities located far away from the gas bubble in these oligotrophic environments (Basso et al, 2009), according to the Subsurface Lithoautotrophic Microbial Ecosystems principle (Stevens & McKinley, ; Pedersen, ; Chapelle et al ., ; Freund et al ., ; Lin et al ., ; Takai et al ., ; Crespo‐Medina et al ., ).…”

Thriving Microbial Life in Ancient Groundwater Deep Inside Earth’s Crust

“…Hydrogen-using bacteria (called Dethiobacter) dominated our microcosms. Our previous study showed that these microbes are playing a big role in formation of the microbial community in deep bedrock [3]. These organisms were also found by another study describing microbial communities enriched from serpentinizing groundwater [4].…”