This work aimed to assess the effectiveness of different in situ bioremediation treatments (bioaugmentation, biostimulation, bioaugmentation and biostimulation, and natural attenuation) on creosote polluted soil. Toxicity, microbial respiration, creosote degradation and the evolution of bacterial communities were analyzed. Results showed that creosote decreased significantly in all treatments, and no significant differences were found between treatments. However, some specific polycyclic aromatic hydrocarbons (PAH) were degraded to a greater extent by biostimulation. The dominance of low temperatures (8.9 degrees C average) slowed down microbial creosote and PAH uptake and, despite significantly creosote degradation (>60%) at the end of the experiment, toxicity remained constant and high throughout the biodegradation process. DGGE results revealed that biostimulation showed the highest microbial biodiversity, although at the end of the biodegradation process, community composition in all treatments was different from that of the control assay (unpolluted soil). The active uncultured bacteria belonged to the genera Pseudomonas, Sphingomonas, Flexibacter, Pantoea and Balneimonas, the latter two of which have not been previously described as PAH degraders. The majority of the species identified during the creosote biodegradation belonged to Pseudomonas genus, which has been widely studied in bioremediation processes. Results confirmed that some bacteria have an intrinsic capacity to degrade the creosote without previous exposure. (C) 2013 Elsevier B.V. All rights reserved.