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 Hunxe, G ermany. Cores were removed along a transect bordering a plume containi ng various monoaromatic hydrocarbons. Monoaromatic hydrocarbons could not be detected in the unsaturated zone in any core but were present i n the saturated zones of core C (between 280 and 42600 mu mol kg(-1) o f core material [dry wt.]) and cores A and B (between 30 and 190 mu mo l kg(-1) of core material [dry wt.]). Xylene isomers accounted for 50- 70% of monoaromatic hydrocarbons in all cores. The number of DAPI-stai ned bacteria was found to increase from the low-contaminated cores A a nd B (approx, 0.1 x 10(8) cells and 0.2 x 10(8) cells g(-1) of core ma terial [dry wt.], respectively) to the high-contaminated core C (2.4 x 10(8) cells g(-1) of core material [dry wt.]). The higher bacterial n umbers in core C were found to coincide with a higher detection rate o btained by in situ hybridization using probe Eub338 to target the doma in Bacteria (13-42% for core C as compared to 3-25% for cores A and B, respectively). Proteobacteria of the delta-subdivision (which include s many sulfate-reducing bacteria) were the most predominant of the gro ups investigated (7-15% of DAPI-stained bacteria) and were followed by Proteobacteria of the gamma- and beta-subdivisions (4% and 1% of DAPI -stained bacteria, respectively). The total numbers of protozoa and ba cteria determined by direct counting occurred in a ratio of approx, 1: 10(3), which was independent of depth or core examined. Most probable number analysis combined with a subsequent classification of the cultu rable protozoa revealed nanoflagellates as the major component of the protozoan community. Naked amoebae became increasingly more encysted w ith depth, except in the high-contaminated core C where vegetative tro phozoites were present in the saturated zone. The co-occurrence of bac teria and protozoa in association with high concentrations of monoarom atic hydrocarbons suggests the involvement of trophic interactions in the process of biodegradation. (C) 1998 Federation of European Microbi ological Societies. Published by Elsevier Science B.V. All rights rese rved.