Analysis of bacterial and protozoan communities in an aquifer contaminated with monoaromatic hydrocarbons

Bacterial and protozoan communities were examined in three cores (A, B and C) from an aquifer located at an abandoned refinery near Hünxe, Germany. Cores were removed along a transect bordering a plume containing various monoaromatic hydrocarbons. Monoaromatic hydrocarbons could not be detected in the unsaturated zone in any core but were present in the saturated zones of core C (between 280 and 42 600 μmol kg−1 of core material [dry wt.]) and cores A and B (between 30 and 190 μmol kg−1 of core material [dry wt.]). Xylene isomers accounted for 50-70% of monoaromatic hydrocarbons in all cores. The number of DAPI-stained bacteria was found to increase from the low-contaminated cores A and B (approx. 0.1×108 cells and 0.2×108 cells g−1 of core material [dry wt.], respectively) to the high-contaminated core C (2.4×108 cells g−1 of core material [dry wt.]). The higher bacterial numbers in core C were found to coincide with a higher detection rate obtained by in situ hybridization using probe Eub338 to target the domain Bacteria (13-42% for core C as compared to 3-25% for cores A and B, respectively). Proteobacteria of the δ-subdivision (which includes many sulfate-reducing bacteria) were the most predominant of the groups investigated (7-15% of DAPI-stained bacteria) and were followed by Proteobacteria of the γ- and β-subdivisions (4% and 1% of DAPI-stained bacteria, respectively). The total numbers of protozoa and bacteria determined by direct counting occurred in a ratio of approx. 1:103, which was independent of depth or core examined. Most probable number analysis combined with a subsequent classification of the culturable protozoa revealed nanoflagellates as the major component of the protozoan community. Naked amoebae became increasingly more encysted with depth, except in the high-contaminated core C where vegetative trophozoites were present in the saturated zone. The co-occurrence of bacteria and protozoa in association with high concentrations of monoaromatic hydrocarbons suggests the involvement of trophic interactions in the process of biodegradatio

Tracing toluene-assimilating sulfate-reducing bacteria using 13C-incorporation in fatty acids and whole-cell hybridization

Polar lipid-derived fatty acids (PLFA) commonly found in sulfate-reducing bacteria were detected in high abundance in the sediment harvested from a monitoring well of a petroleum-hydrocarbon (PHC)-contaminated aquifer. Aquifer microcosms were incubated under sulfate-reducing conditions with [methyl-14C]toluene to determine the 14C-mass balances and with [methyl-13C]toluene to follow the flow of carbon from toluene into biomarker fatty acids. An aliquot was used to establish an aquifer-derived toluene-degrading sulfate-reducing consortium, which grew well in liquid medium. Whole-cell hybridization using 16S rRNA-targeted oligonucleotide probes specific for different phylogenetic levels within the sulfate-reducing bacteria was applied in order to characterize the sulfate-reducing populations in the original sediment, the aquifer microcosms, and the aquifer-derived consortium. In the aquifer microcosms, the 14C quantification revealed that 61.6% of the [methyl-14C]toluene was mineralized and 2.7% was assimilated. Following [methyl-13C]toluene depletion (<1 μM), the highest 13C-enrichment was found in PLFA 16:1ω5c. In addition, biomarker fatty acids characteristic for the genera Desulfobacter and Desulfobacula (cy17:0 and 10Me16:0) were also 13C-enriched, contrary to those of other sulfate-reducing genera, e.g. Desulfovibrio and Synthrophobacter (i17:1ω7c), Desulfobulbus and Desulforhabdus (15:1ω6c and 17:1ω6c). Although hybridization detection rates remained low, indicating low bacterial activities, 43% (aquifer sediment) and 30% (aquifer microcosm) of the total active bacteria belonged to the Desulfobacteriaceae thus supporting the PLFA-based results. Desulfobacter-species (42%), which belong to the Desulfobacteriaceae, dominated the community of the consortium. Our study showed that carbon stable isotope analysis in combination with whole-cell hybridization could link toluene degradation in aquifer microcosms to the metabolic activity of the Desulfobacter-like populations. These populations could play an important role in the clean up of aromatic PHC-contaminated aquifer

Analysis of bacterial and protozoan communities in an aquifer contaminated with monoaromatic hydrocarbons

ISSN:0168-6496ISSN:1574-694