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Although polycyclic aromatic hydrocarbons (PAH) and alkanes are biodegradable at ambient temperature, in some cases low bioavailabilities are the reason for slow biodegradation. Considerably higher mass transfer rates and PAH solubilities and hence bioavailabilities can be obtained at higher temperatures. Mixed and pure cultures of aerobic, extreme thermophilic microorganisms (Bacillus spp., Thermus sp.) were used to degrade PAH compounds and PAH/alkane mixtures at 65 degrees C. The microorganisms used grew on hydrocarbons as sole carbon and energy source. Optimal growth temperatures were in the range of 60-70 degrees C at pH values of 6-7. The conversion of PAH with 3-5 rings (acenaphthene, fluoranthene, pyrene, benzo[e]pyrene) was demonstrated. Efficient PAH biodegradation required a second, degradable liquid phase. Thermus brockii Hamburg metabolized up to 40 mg (1 h)(-1) pyrene and 1000 mg (1 h)(-1) hexadecane at 70 degrees C. Specific growth rates of 0.43 h(-1) were measured for this strain with hexadecane/pyrene mixtures as the sole carbon and energy source in a 2-liter stirred bioreactor. About 0.7 g cell dry weight were formed from 1 g hydrocarbon. The experiments demonstrate the feasibility and efficiency of extreme thermophilic PAH and alkane biodegradation.

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