Propylene glycol-specific dehydrogenases as functional biomarkers for monitoring biodegradation in sites contaminated by de-icing chemicals

The area under study at Gardermoen airport (Oslo, Norway) is a glacial contact formation with sand and gravels dominating near the ground surface. Due to the northern climate, every winter large amounts of de-icing chemicals, i.e. propylene glycol (PG) and potassium formate, are commonly used in the airport for the removal of snow and ice from airplanes and runways, respectively. Even though these contaminants are easily degradable by biotic or abiotic factors, they may still threaten groundwater, due to the system overloading. The present study, performed within the FPVII European research project: “SoilCAM - Soil Contamination: Advanced integrated characterisation and time-lapse Monitoring”, deals with the physic-chemical and microbiological characterization of the site and the development of suitable methods for monitoring PG biodegradation on site under reclamation. For this purpose, functional biomarkers were selected to evaluate their potential use in Real Time quantitative PCR (q-PCR) experiments directly on soil DNA. The soils are highly leached, with low biological and biochemical activities. Therefore, pollutant transfer to the groundwater occurs quickly and is virtually unhindered. Bacterial strains isolated from the soil were able to degrade PG in aerobic conditions at 4, 15 and 30 °C. The PG-degrading population was mainly composed by different species of Pseudomonas, as shown by denaturing gradient gel electrophoresis (DGGE) analysis on soil DNA. Gene probes for PG-specific alcohol dehydrogenase (ADH-IIG) detected the presence of such genes in the isolates. The deduced amino acid sequence of representative strains presented over 92% identities with PG-specific dehydrogenase-related proteins. ADH-IIG detected in soil DNA indicated that PG-degrading strains were present along the soil profile from 0 to 100 cm. The application of q-PCR analysis on DNA from soil mesocosm experiments will confirm the suitability of ADH-IIG as biomarker for monitoring PG biodegradation in soil systems.