Bacterial diversity in groundwater of three hard-rock aquifers in the Armorican massif (Brittany, France)

Hard-rock aquifers are widespread subsurface habitats that are readily colonized by microorganisms. These environments are characterized by heterogeneous hydrologic circulation, which strongly constrains groundwater residence time, hydrochemistry, and nutrient supply. However, little is known about the effects of hydrologic circulation on microbial communities. Groundwater of different ages (residence time) was sampled along hydrogeologic flow paths in three contrasting hard-rock aquifers in Brittany (France). Residence time and a wide range of environmental factors were used to test the influence of groundwater circulation on active microbial community composition, assessed by community RNA extraction and 454 sequencing of 16S rRNA amplicons.