Microbial adaptation to degradation of hydrocarbons in polluted and unpolluted groundwater

The microbial adaptation to degradation of aromatic hydrocarbons in heavily polluted, slightly polluted and unpolluted groundwater was examined. In addition, adaptations of bacteria from aquifers polluted by fuel oil and gasoline were compared. Finally, it was tested whether addition of bacteria attached to subsurface soil, originating from the same wells as the groundwater had any effect on the degradation. The compounds used as substrate were: toluene, o-xylene, 1,3,5-trimethylbenzene, naphthalene, 1-methylnaphthalene, biphenyl, 2-ethylnaphthalene, and 1,4-dimethylnaphthalene. Initial concentrations of each component were in the range of 100 μg L −1 to 240 μg L −1. A simple techniques was used. The lengths of the lag periods were used to express the degree of adaptation to degradation of the hydrocarbons. In one experiment equal volumes of groundwater from the three sites were used as inoculum. In another experiment equal microbial numbers in the bottles were ensured by adding different volumes of groundwater. The experiments demonstrate that the bacterial community in the heavily polluted well has a higher degree of adaptation to hydrocarbon degradation than the community from the slightly polluted well. The bacteria from the unpolluted well are considered as being unadapted, because of long lag periods compared to the bacteria in the polluted wells (7 to 34 times longer). The sequence in which the compounds were degraded after inoculation with fuel oil polluted or gasoline polluted groundwater is related to the occurrence of these compounds in the water soluble fractions of the two petroleum products. Addition of soil reduced the lag periods in the bottles inoculated with heavily polluted groundwater, while no or minor effects were observed, when added to the bottles inoculated with slightly or unpolluted groundwater. During the experimental periods an increase in ATP content was observed.