Initial microbial degradation of polycyclic aromatic hydrocarbons

The group of polycyclic aromatic hydrocarbons (PAHs) are very hazardous environmental pollutants because of their mutagenic, carcinogenic and toxic effects on living systems. The aim of this study was to examine and compare the ability and efficiency of selected bacterial isolates obtained from oil-contaminated areas to biodegrade PAHs. The potential of the bacteria to biodegrade various aromatic hydrocarbons was assessed using the 2,6-dichlorophenol-indophenol assay. Further biodegradation of PAHs was monitored by gravimetric and gas-chromatographic analysis. Among the eight bacterial isolates, identified on the basis of 16S rDNA sequences, two isolates, Planomicrobium sp. RNP01 and Rhodococcus sp. RNP05, had the ability to grow on and utilize almost all examined hydrocarbons. Those isolates were further examined for biodegradation of phenanthrene and pyrene, as single substrates, and as a mixture, in vitro for ten days. After three days, both isolates degraded a significant amount phenanthrene, which has a simpler chemical structure than pyrene. Planomicrobium sp.RNP01 commenced biodegradation of pyrene in the PAH mixture only after it had almost completly degraded phenanthrene. The isolated and characterized bacteria, Planomicrobium sp. RNP01 and Rhodococcus sp. RNP05, have shown high bioremediation potential and are likely candidates to be used for degradation of highly toxic PAHs in contaminated areas.