Isolation and Selection of a Highly Tolerant Microbial Consortium with Potential for PAH Biodegradation from Heavy Crude Oil-Contaminated Soils

A degrading microbial consortium highly tolerant to three-, four- and five-ring polycyclic aromatic hydrocarbons (PAHs) was selected from 50 fungal and bacterial isolates obtained from crude oil-contaminated soils. Morphological and molecular studies indicated that isolated fungi belonged to genera Aspergillus, Penicillium, Fusarium, Trichoderma, Scedosporium, and Acremonium and bacteria to Pseudomonas, Klebsiella, Bacillus, Enterobacter, Streptomyces, Stenotrophomonas, Kocuria, and Delftia genera. Individual fungal and bacterial isolates were evaluated for their potential to tolerate high concentrations of different molecular weight PAHs, as phenantrene (Phe), pyrene (Pyr), and benzo[a]pyrene (BaP) by surface plate assays, showing significant differences in extension rates for fungi and inhibition ratios for bacteria when both were exposed to 0–6,000 mg of PAHs per liter. Trichoderma asperellum H15, Aspergillus nomius H7, Aspergillus flavus H6, Pseudomonas aeruginosa B7, Klebsiella sp. B10, and Stenotrophomonas maltophilia B14 grew using PAHs as sole carbon source and presented a remarkably high tolerance to PAHs, up to 6,000 mg l⁻¹. The consortium composed of 12 fungal and bacterial PAH-tolerant isolates for the bioremediation of a PAH-contaminated soiled to a removal of 87.76 % Phe, 48.18 % Pyr, and 56.55 % BaP after 14 days. The degrading microbial consortium presented high potential for bioremediation and may be useful for the treatment of sites polluted with PAHs due to their elevated tolerance to high molecular weight (HMW) PAHs and their capacity to utilize them as energy source. This is the first study which evaluated the microbial tolerance to extreme concentrations of PAHs, resulting in a degrading consortium and highly tolerant consortium compared with those reported in other studies, where the concentrations tested are low.