PAH Biodegradation by Rhizobia in the Presence of Heavy Metals

The physiological and biochemical characteristics of rhizobia can be of great importance for the bioremediation of soils contaminated with a complex of organic and inorganic pollutants. In the present work, we investigated the biodegradation of the polycyclic aromatic hydrocarbon (PAH) phenanthrene and resistance to heavy metals (cadmium, nickel, copper, and zinc) in rhizobial strains of the genera Ensifer and Neorhizobium from the Collection of Rhizosphere Microorganisms, Institute of Biochemistry and Physiology of Plants and Microorganisms. Bacterial growth and phenanthrene biodegradation in the presence of these metals were characterized. The effect of metals on the activity of bacterial enzymes phenanthrenequinone reductase and protocatechuate dioxygenase has been demonstrated. This is the first report on phenanthrenequinone reductase activity in rhizobia. The results obtained may suggest the successful use of rhizobia in the processes of bioremediation of combined soil contamination with PAHs and heavy metals.