). Amplified 16S rRNA genes were purified using the UltraClean PCR Clean-Up DNA Purification Kit (MO BIO Laboratories Inc.), and clone libraries were prepared using the TOPO TA Cloning Kit with the pCR2.1-TOPO vector (Invitrogen). Plasmid DNA from clones from each DNA extract was purified using the UltraClean 6 min Mini Plasmid Prep Kit (MO Sirolimus mouse BIO Laboratories Inc.). Twenty-five

microlitres of the purified plasmids were used for sequencing performed at Eurofins MWG Operon Inc. (Ebersberg, Germany). The aim was to sequence five clones from each analysed well. The 16S rRNA gene sequences were aligned to sequences from the GenBank database. Analysis of the contaminated soils showed different hydrocarbons (Table 1). A control subsurface soil was sampled at an area of St. Nord without any known contamination. The dry matter contents of the contaminated soil and subsoil were determined to be 92.2% and 91.7% and the pristine control soil had a dry matter content of 86.2%. Among the PAHs included in the analysis, naphthalene was detected at the highest concentration in the contaminated top soil, with 7.34 mg kg−1 dry weight (DW) soil, and the concentration was reduced Trichostatin A nmr to 0.72 mg kg−1 DW soil in the subsoil (Table 1). Lower concentrations of phenanthrene, acenaphthylene, acenaphthene, antracene and fluorene were detected in both contaminated

soils. The phenanthrene concentration in the top soil was 0.20 mg kg−1 DW soil, and the concentrations were reduced to 0.06 mg kg−1 DW soil in the subsoil. Traces of fluoranthene, pyrene, chrysene, benzo[b+j+k]fluoranthene and benzo[e]pyrene were detected in the polluted top soil, but not in the deeper Janus kinase (JAK) soil. Benzo[a]anthracene, benzo[a]pyrene, indeno[1,2,3-cd]pyrene, dibenz[a,h]anthracene and benzo[ghi]perylene were not detected in any of the three soils analysed. None of

the PAHs included in the soil characterization were measured in the pristine soil. Overall, 16 000 mg kg−1 DW soil hydrocarbons were detected in the polluted top soil and 4500 mg kg−1 DW soil in the polluted subsoil, and no hydrocarbons were detected in the pristine soil (Table 1). The two contaminated soils appeared to be affected by fuels and both smelled and looked highly impacted. We therefore determined whether the microbial communities associated with these contaminated soils were metabolically active by measuring the [14C]benzoic acid mineralization to 14CO2 for 150 days. We also tested the phenanthrene mineralization, selected as a model compound, in the two contaminated soils and in one pristine soil at −5 and 0 °C. At 0 °C, benzoic acid was metabolized in all three tested soils (Fig. 1a), and the fastest mineralization was observed in the top soil, where most of the activity occurred during the first 14 days, with 58–60% of the added [14C]benzoic acid metabolized to 14CO2. Slower metabolism was apparent in the subsurface and pristine soils, where 28.5 ± 2.5% and 10.3 ± 2.