|Grösbacher, M; Spicher, C; Bayer, A; Obst, M; Karwautz, C; Pilloni, G; Wachsmann, M; Scherb, H; Griebler, C: Organic contamination versus mineral properties: competing selective forces shaping bacterial community assembly in aquifer sediments, Aquatic Microbial Ecology, 76, 243-255 (2016), doi:10.3354/ame01781 [Link]|
Multiple factors have been shown to influ- ence the assembly of sediment microbial communities. We hypothesized that in an organically polluted aquifer, the degree of contamination controls bacterial distribution pat- terns, superimposing other selective forces such as sedi- ment and mineral properties. Groundwater and sediment samples were analyzed from distinct zones of a petroleum hydrocarbon contaminated sandy aquifer that correspond to different degrees of contamination: Zone 1, with a high concentration of dissolved contaminants (benzene, toluene, ethylbenzene, and xylenes); Zone 2, with high concentra- tions of sediment-bound polycyclic aromatic hydrocarbons (PAHs); and Zone 3, with only minor PAH contamination. Sediment analysis concentrated on 2 mineral fractions dif- fering in many sediment properties, i.e. translucent quartz (TQ) and mica. Sediment bacterial communities were ana- lyzed by DNA fingerprinting (terminal restriction fragment length polymorphism) and total cell counts. While Zone 1 exhibited highly similar communities on TQ and mica, the selective sorption of PAHs to mica revealed sediment bac- terial communities with hardly any taxonomic units shared in Zone 2. Typical selective forces active in sediments of oligotrophic habitats, such as sediment mineral content and surface roughness, only gained influence in Zone 3. Similarly, the least contamination revealed the most pro- nounced differences in Shannon diversity, evenness, and total cell counts between the mineral fractions tested, with mica characterized by highest biomass and bacterial diver- sity. The role of contamination as a selective force is also underlined by the zone-specific dominance of key microbes involved in petroleum hydrocarbon degradation. Our re- sults demonstrate that typical selective forces shaping aquifer sediment microbial communities are outcompeted by organic contamination.