Sampling methods for characterization of microbial communities in aquifers should
target both suspended and attached microorganisms (biofilms). We investigated the
effectiveness and reproducibility of low-frequency (200 Hz) sonication pulses on improving
extraction efficiency and quality of microorganisms from a petroleum-contaminated
aquifer in Studen (Switzerland). Sonication pulses at different power levels (0.65,
0.9, and 1.1 kW) were applied to three different groundwater monitoring wells. Groundwater
samples extracted after each pulse were compared with background groundwater samples
for cell and adenosine tri-phosphate concentration. Turbidity values were obtained
to assess the release of sediment fines and associated microorganisms. The bacterial
community in extracted groundwater samples was analyzed by terminal-restriction-fragment-length
polymorphism and compared with communities obtained from background groundwater samples
and from sediment cores. Sonication enhanced the extraction efficiency up to 13-fold,
with most of the biomass being associated with the sediment fines extracted with groundwater.
Consecutive pulses at constant power were decreasingly effective, while pulses with
higher power yielded the best results both in terms of extraction efficiency and quality.
Our results indicate that low-frequency sonication may be a viable and cost-effective
tool to improve the extraction of microorganisms from aquifers, taking advantage of
existing groundwater monitoring wells.