Natural Attenuation and Bioaugmentation on PAH Degradation and Microbial Community in Soil Contaminated with Phenanthrene and Pyrene

COPPOTELLI B.M., DEL PANNO M.T. AND MORELLI I.S

Bogotá, Colombia

Simposio; VI Simposio Latinoamericano De Biodegradación y Biodeterioro 6LABS – 2007; 2007

CYTED

Polycyclic aromatic hydrocarbons (PAH) are widely distributed in the ecosphere as a result of fossil fuel combustion and industrial activities. They are toxic, mutagenic and carcinogenic. Bioremediation strategies as natural attenuation and bioaugmentation are considered to be a promising approach to remediate PAH-contaminated soils. Although little is known about how the PAH contamination and the inoculant impact on the indigenous microbial community. In this study, the PAH elimination rate and the soil microbial community-level responses to phenanthrene and pyrene contamination and to the inoculation with a  phenanthrene degrader strain Sphingomonas paucimobilis 20006FA, were studied in soil microcosms with 2000 mg of phenanthrene and 1000 mg of pyrene per Kg of dry soil (F+P).  Periodically, PAH concentration (GC-FID), the number of cultivable heterotrophic bacteria (R2A-agar), PAH degrading bacteria (MPN) and biological activity (dehydrogenase activity) were determined. Genetic diversity profiles of the bacterial communities were analyzed using PCR-DGGE. Compared with the microcosms contaminated just with one PAH, the F+P microcosm showed a higher initial PAH elimination rate, with significantly lower cells density, biological activity and higher residual PAH concentration (after 50 days of treatment). In the inoculated microcosms a marked increase in cells density and dehydrogenase activity were observed, but the inoculum did not cause significant changes in the initial PAH elimination rate and it was strongly affected the pyrene degradation. The DGGE patterns of inoculated microcosms showed a remarkable dominance of S. paucimobilis 20006FA with a significant reduction in the number of bands in comparison with the non inoculated microcosm. Cometabolism could explain the rapid degradation of PAH during the initial phase of the treatment in F+P microcosms. The profound shift in the composition of soil microbial community caused by the contamination with phenanthrene and pyrene and the presence of the inoculant might explain the incomplete biodegradation of PAH.