Isolation and characterization of diaryl ester catabolizing soil fungi.

Abstract

Aromatic hydrocarbons are major organic pollutants that can persist in the environment. However, many fungi and yeasts can utilize these compounds as carbon and energy sources under aerobic conditions. Salol and benzyl salicylate are diaryl ester biocides exhibiting endocrine-disrupting properties. Using mineral salts medium containing salol and benzyl salicylate as sole carbon and energy source, aerobic enrichment cultures were established by inoculation with soil samples collected from a local animal farm and Bisley Nature Reserve Pietermaritzburg, KwaZulu-Natal. A salol utilizing fungal isolate and a benzyl salicylate utilizing yeast isolate were selected after enrichment. The fungal and yeast isolate were provisionally assigned to the genus Fusarium and Trichosporon, based on phenotypic characteristics and the sequence analysis of the ITS1-5.8S rRNA-ITS2 region. Growth kinetics of the fungus were assessed by measuring the dry weight of the biomass over time in batch cultures; the growth of the yeast was assessed via OD600 determinations and verified via microscopic cell counts. Appropriate abiotic controls showed that the concentration of tested aromatic pollutants remained stable over time while no biomass formed in biotic controls without added carbon source. Salol and benzyl salicylate utilization was verified by measuring the Chemical Oxygen Demand (COD) and UV-Vis spectra over time. COD measurements and UV spectroscopy indicated that up to 10 mM salol was catabolized completely by Fusarium sp. strain VM1 within 10 days while Trichosporon sp. strain VM2 catabolized 10 mM benzyl salicylate almost quantitatively. Specific enzyme activity determinations showed that both esterase and catechol-1,2-dioxygenase were induced by growth on salol and benzyl salicylate, indicating that the catabolism of diaryl esters is initiated by hydrolysis of the ester-linkage and the monoaromatic hydrolysis products were further metabolized via catechol and the ortho-pathway. These results indicate that members of the genus Fusarium and Trichosporon present in South African soils have the potential to eliminate diaryl esters and simple monoaromatic pollutants.