Spatial and temporal changes in Actinobacterial dominance in experimental artificial groundwater recharge

Artificial groundwater recharge (AGR) is used in the drinking water industry to supplement groundwater resources and to minimise the use of chemicals in water treatment. This study analysed the spatial and temporal changes of microbial communities in AGR using two test systems: a nutrient-amended fluidized-bed reactor (FBR) and a sand column. Structural changes in the feed lake water (Lake Roine), FBR, and sand column bacterial communities were determined by denaturing gradient gel electrophoresis (DGGE) and the length heterogeneity analysis of amplified 16S rRNA genes (LH-PCR). Two clone libraries were created to link the LH-PCR results to the dominant bacterial groups. The lake water bacterial community was relatively stable, with three bands dominating in all LH-PCR products. The most dominant fragment accounted for up to 72% and was derived from Actinobacteria. Based on the clone libraries and LH-PCR data, Actinobacteria also dominated in the unattached bacterial community of the FBR, whereas several Proteobacterial groups were more abundant on the FBR carrier particles. In the stabilised AGR system a major change in the community structure of the lake water bacteria took place during passage within the first 0.6 m in the sand column as the community composition shifted from Actinobacteria-dominated populations to a diverse, mainly Proteobacterial communities. Concurrently, most of the dissolved organic carbon (DOC) was removed at this stage. In summary, the study showed that the make-up of microbial communities in experimental AGR systems responded to changes in their environment. LH-PCR showed potential as a method to determine microbial community dynamics in long-term studies at real-scale AGR sites. This is the first step to provide data on microbial community dynamics in AGR for drinking water production.