Polycyclic aromatic hydrocarbons (PAHs) are potent carcinogens produced by various activities ranging from grilling meat to coal gasification. Our project aims to degrade high molecular weight PAHs present in industrial waste from district heating plants. There is currently no sustainable way to handle this waste and therefore it is deposited in landfills. We want to solve this problem by employing a bacterial based system.
Our cells need to be able to detect the PAHs for direct degradation. However the high molecular weight PAHs do not readily pass through the cell membrane. We solved this obstacle by using the low weight PAH, naphthalene, as an indicator for the presence of heavier PAHs. The degradation of this small PAH inside the cell relieves repression of genes under the control of the NahR/Psal promoter system. This causes the expression of a series of enzymes for PAH degradation which are secreted outside the cell where they can oxidize and cleave the ring structures of the carcinogenic compounds. This in turn makes them available for downstream biodegradation. To increase the degradation efficiency, our system also produces rhamnolipids. These are biosurfactants that prevent the PAHs from aggregating, making them easier for the enzymes to access.