No abstract

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.

Microbial characterization of aquifers should combine collection of suspended and attached microorganisms (biofilms). This study investigated chemical extraction of microorganisms from water-saturated, packed sediment containing established biofilms. It compares the use of different detachment-promoting agent (DPA) solutions with tap water as eluent in column experiments. Extraction efficiency was determined from cell concentrations in the column effluent. Adenosine triphosphate concentrations were measured to confirm cell extraction and as an indicator of cell membrane integrity. Quality of extracted bacterial communities was assessed by comparing their terminal restriction fragment length polymorphism profiles with destructively sampled sediment-community profiles. Extraction efficiency increased more than 8-fold when deionized water, D-amino acids, or enzymes were used as a DPA. Community profiles recovered by individual DPA solutions showed more pronounced differences at the level of rare microbial groups, whereas abundant groups appeared ubiquitous across treatments. These results suggest that comparison of communities extracted by different DPAs can provide improved information on the occurrence of rare microbial groups in biofilms.

These findings illustrate for the first time that the lack of specific antibodies against streptococcal virulence factors, such as streptokinase, may contribute to NF disease severity. This can be counteracted by ex-IgGs.