The accidental release of fuel oils into the environment happens frequently, not only as a consequence of spec- tacular oil tanker spills, but also on a smaller scale along pipelines, or during filling of containers and tanks at gas stations and heating plants. Treatment of contaminated soils can be carried out by physicochemical methods (see ref. [1]), such as thermal destruction of hydrocarbons [2], which is rather tedious and can be extremely expensive. It is generally agreed upon that bioremediation – the degradation of contaminants in situ by suitable bacterial strains – is a much more sustainable method and should be used whenever possible [3, 4]. Several factors such as the composition of soils, the presence of nutrients or the augmentation with such substances, temperature, pH, and other environmental parameters as well as added chemicals will influence the efficiency of degradation [1, 4]. Members of the bacterial genus Pseudomonas are known to degrade numerous petroleum compounds, such as alkanes, S- and N-heterocycles, and polyaromatic hy- drocarbons [5]; other bacteria and microorganisms, no- tably fungi, have also been described as suitably efficient for degradation [4]. However, while impressive rates of degradation of hydrocarbons have been reached in the laboratory with pure cultures of strains (e.g., [6, 7]) and the genetics of hydrocarbon degradation by singular species are beginning to be understood [1, 8], it is more sensible to use bacterial consortia, when in situ remediation is in- tended, since oil contains a mixture of hydrocarbons [3] and a consortium would be more efficient for cleavage and metabolization of various compounds. Reintroduc- tion of indigenous microorganisms into polluted environ- ments appears especially effective, particularly when fer- tilizers are added [4]. Since toxic byproducts can emerge during treatment, which could slow down degradation processes, and may impair the future use of the soil [9], Technical Report Biodegradation of fuel oil hydrocarbons by a mixed bacterial consortium in sandy and loamy soils Elisabeth Hawle-Ambrosch 1 , Wolfgang Riepe 1 , Marion Dornmayr-Pfaffenhuemer 2 , Christian Radax 3 , Anita Holzinger 2 and Helga Stan-Lotter 2 1 Division of Molecular Biology, Department of Chemistry, University of Salzburg, Salzburg, Austria 2 Division of Molecular Biology, Department of Microbiology, University of Salzburg, Salzburg, Austria 3 Salzburg, Austria The aerobic degradation of light fuel oil in sandy and loamy soils by an environmental bacterial consortium was investigated. Soils were spiked with 1 or 0.1% of oil per dry weight of soil. Acetone extracts of dried soils were analyzed by GC and the overall degradation was calculated by com- parison with hydrocarbon recovery from uninoculated soils. In sandy soils, the sum of alkanes n-C 12 to n-C 23 was degraded to about 45% within 6 days at 20°C and to 27–31% within 28 days, provided that moisture and nutrients were replenished. Degradation in loamy soil was about 12% lower. The distribution of recovered alkanes suggested a preferential degradation of shorter chain molecules (n-C 12 to n-C 16 ) by the bacterial consortium. Partial 16S rDNA sequences indicated the presence of strains of Pseudomonas aeruginosa, Pseudomonas citronellolis, and Stenotrophomonas maltophilia. Toxicity tests using commercial standard procedures showed a moderate inhibition of bacterial activity. The study showed the applicability of a natural microbial community for the degradation of oil spills into soils at ambient temperatures. Keywords: Bacterial degradation · Bioremediation · Fuel oil · Hydrocarbon chains Correspondence: Professor Dr. Helga Stan-Lotter, Division of Molecular Biology, Department of Microbiology, University of Salzburg, Billrothstr. 11, Salzburg A-5020, Austria E-mail: helga.stan-lotter@sbg.ac.at Fax: +43-662-8044-7209 Received 4 May 2007 Revised 31 May 2007 Accepted 28 June 2007 Biotechnology Journal DOI 10.1002/biot.200700082 Biotechnol. J. 2007, 2, 1564–1568 1564 © 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim