Isolation and characterization of pyrene metabolizing microbial consortia from the plant rhizoplane

Most research on the ecology of PAH degrading bacteria in the rhizosphere has focused on individual strains that grow on specific PAHs. Thus, there are fundamental questions as to importance of microbial consortia for PAH degradation in the plant rhizosphere. The study reported here characterized cultivable pyrene degrading rhizoplane microbial communities from two different plant species using a root printing technique on agar plates. Colonies were revealed by formation of clearing zones on medium containing a thin film of pyrene on the surface of a mineral nutrient agar. Prints of the rhizoplane colonies were obtained from roots of Melilotus officinalis (sweet yellow clover) and Andropogon gerardii (big bluestem) plants. Phylogenetic characterizations of selected pyrene degrading colonies were assessed by PCR-DGGE and DNA sequencing. Results showed that different populations of cultivable pyrene degraders were obtained from representative consortia that were examined. Many of the PAH degrading consortia consisted of mixtures of bacterial species that were unable to degrade pyrene by themselves. While this study focused on culturable PAH degraders, the results suggest that pyrene degradation in the rhizosphere commonly involves the activity of bacterial consortia in which various species of bacteria interact to achieve PAH degradation.