PAHBioremediation by Microbial Communities and Enzymatic Activities

Abstract

Polycyclic aromatic hydrocarbons (PAHs) are hydrophobic, persistent, ubiquitous pollutants of the environment. The capability for PAH degradation of soil indigenous microorganisms has been investigated in numerous studies. PAH‐degrading bacteria have been found in pristine and contaminated temperate and tropical zone ecosystems, in Arctic and Antarctic soils, in sediments and in the rhizosphere of numerous different plants. A broad range of oxygenases is distributed among the microorganisms growing on PAHs and several groups of genes for the initial PAH oxygenation are now known. Gene sequences encoding for enzymes specific for the initial and ring oxygenase have been used to construct specific probes. The broad biodegradative capabilities evolved by microorganisms towards these compounds and the available tools for monitoring their presence in the environment account for bioremediation‐based strategies with the potential to restore PAH‐contaminated soils. Compost and composting matrices have enormous potential for assisting the bioremediation of PAH‐polluted soils and both techniques have been successfully applied to ameliorate soil contaminated with PAHs. One way to achieve truly in situ bioremediation is by utilizing plants to perform rhizosphere bioremediation. Phytoremediation is of particular interest as a secondary polishing approach for PAH‐contaminated soil previously treated by land farming, augmentation of the soil with selected PAH‐degrading bacteria and growth of plants with plant growth‐promoting rhizobacteria. A different approach, alternative to whole microbial and plant cells, is the use of extracellular enzymes, such as oxidoreductases of fungal origin with known abilities to transform or even to degrade PAHs effectively.

Potential for the Use of Rhizobacteria in the Sustainable Management of Contaminated Soils

“…Bacteria degrade xenobiotics through a variety of enzymes including peroxidases, monooxygenases and dioxygenases, laccases, phosphatases, dehalogenases, nitrilases, and nitroreductases (Siciliano et al 2001;Gibson and Parales 2000;Gianfreda and Rao 2004;Andreoni and Gianfreda 2009). Although some microorganisms can completely degrade a specific xenobiotic, individual species generally do not contain entire degradation pathways.…”