The function of a community of toluene-degrading bacteria in a biofilm system was investigated with regard to growth and toluene degradation in order to investigate substrate interactions in the community. This was done by the combination of experimental observations using a specific oligonucleotide 16S ribosomal RNA probe targeting the toluene-degrading species Pseudomonas putida, and by computer simulations (AQUASIM) of the biofilm growth based on a food web model. Biofilms were taken from a lab-scale trickling filter for treatment of toluene-polluted air. The biofilm growth and the activity of P. putida, a representative of the toluene-degrading species in the biofilm which have been described previously were simulated. The simulation indicated that the volume fraction of the toluene degraders in the biofilm decreased from 12% to only 2% (11% of dry weight) during two weeks. In spite of the low fraction in the biofilm, the toluene degraders supported growth of the dominating part of non-toluene-degrading heterotrophs in the biofilm, as toluene was the sole carbon source supplied to the system. The maximum intrinsic growth rate of P. putida in the biofilm was only 20% of the maximum growth rate determined in a batch experiment with suspended P. putida cells.

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