Degradation of Polycyclic Aromatic Hydrocarbons by Co-Culture of Pleurotus ostreatus Florida and Azospirillum brasilense

Abstract

Bacterial-fungal interactions are important in the functioning of natural ecosystems. We examined possible synergistic or antagonistic effects during the degradation of polycyclic aromatic hydrocarbons (PAHs) by a fungal–bacterial co-culture. Bacteria and fungi were grown in a liquid nutrient medium supplemented with PAH substrates. The degradation of PAHs and the identification of metabolites were checked by HPLC. Enzyme activities were spectrophotometrically measured with test substrates. Compared to monocultures, the co-culture yielded higher mycelium dry weights and higher numbers of bacterial colony-forming units (CFUs). Both organisms and their co-culture transformed three- and four-ring PAHs into the corresponding quinones. The degradation of PAHs was accompanied by the production of fungal extracellular laccase and versatile peroxidase, whose activities were higher in the co-culture than they were in the monocultures. The presence of exogenous indole-3-acetic acid (IAA) boosted PAH degradation and enzyme production. The xylotrophic basidiomycete Pleurotus ostreatus Florida and the plant-growth-promoting rhizobacterium Azospirillum brasilense exerted a positive mutual effect, including increases in mycelium dry weight, number of CFUs, degradation of PAHs, and production of fungal extracellular enzymes. IAA may be a factor in the interactions of P. ostreatus Florida with A. brasilense.