Degradation of a Model Mixture of PAHs by Bacterial-Fungal Co-Cultures

Abstract

Background: Bacteria and fungi are the most important soil organisms owing to their abundance and the key roles they play in the functioning of ecosystems. We examined possible synergistic and antagonistic effects during the degradation of polycyclic aromatic hydrocarbons (PAHs) by co-cultures of ascomycetes and a plant-growth-promoting bacterium. Methods: Bacteria and fungi were grown in a liquid nutrient medium supplemented with PAHs. The PAH degradations and the identification of metabolites were checked by high-performance liquid chromatography (HPLC). Enzymatic activities were measured spectrophotometrically using test substrates. All experimental treatments were analyzed using Excel 2019 (Microsoft Office 2019, USA). Results: The model system included the plant-growth-promoting rhizobacterium (PGPR) Azospirillum brasilense and one of the following ascomycetes: Fusarium oxysporum (plant pathogen), Talaromyces sayulitensis (rhizospheric fungus), Trichoderma viride (plant-growth-promoting fungus, PGPF), and Trichoderma harzianum (PGPF). The notable results are: (1) synergistic effects consisted of more active utilization of the PAH mixture compared to individual compounds, while the PAH mixture was more actively degraded by co-cultures than monocultures; (2) three effects of mutual influence by the studied organisms were also revealed: depressing (F. oxysporum and A. brasilense), partially depressing (T. sayulitensis suppressed the growth of A. brasilense but increased the degradation of anthracene, pyrene, and fluoranthene), and positive effects (A. brasilense and T. viride or T. harzianum); (3) for the first time quinone metabolites of PAH degradation and extracellular oxidase and peroxidase were produced during PAH degradation by T. sayulitensis. Conclusions: The results of the study contribute to the understanding of bacterial-fungal interactions in polluted settings.