Petroleum biodegradation capacity of bacteria and fungi isolated from petroleum-contaminated soil

We investigated the potential for petroleum hydrocarbon biodegradation by 95 bacterial and 160 fungal strains isolated from a former petrochemical plant. We tested whether soil origin, culture media type, and strain taxonomy influenced the degradation of added petroleum hydrocarbon compounds. Preliminary screening was based on two colorimetric tests using 2,6-dichlorophenolindophenol and p-iodonitrotetrazolium indicators, to assess microbial strain tolerance to crude oil. Top-performing strains in these screening assays were then assessed for their ability to mineralize a mixture of four polycyclic aromatic hydrocarbons (PAH) for 49 days, using GC-MS quantification. The aerobic activity of these candidate strains was also assessed by respirometry over the first 24 days of incubation. On average, PAH degradation by microbial isolates from soil that was lightly, moderately, and highly contaminated with petroleum was equally efficient, and the type of culture medium used did not significantly impact mean biodegradation. Phylogenetic affiliation had a strong and significant effect on PAH biodegradation. Fungal isolates belonging to the group Sordariomycetes, and bacterial isolates belonging to the groups Actinobacteria, Betaproteobacteria, and Gammaproteobacteria showed high potential for PAH degradation. Three of the strains tested by GC-MS, Rhodococcus sp., Trichoderma tomentosum, and Fusarium oxysporum, significantly degraded all four PAH compounds in the mixture compared to the control.