Biodegradation of high-molecular-weight aliphatic and aromatic hydrocarbons by Aspergillus calidoustus

It is now realized that fungi, specifically molds, have the potential to eliminate a variety of compounds, especially toxic and heavy hydrocarbons. The aim of this study was to investigate the ability of native mold isolates in biodegradation of petroleum pollutants and also the effect of surface active compounds on the removal efficiency.
Material & Plenty of mold strains were isolated from an oil-contaminated area in Sarkhoon area of Hormozgan state. The capability of these isolates in petroleum biodegradation was studied in a salt-based medium containing one percent crude oil. The superior strain was selected and characterized by Internal transcribed spacer (ITS) gene sequencing analysis. Biodegradation rate of 500 ppm pyrene (heavy aromatic hydrocarbons) and 1% tetracosane (heavy aliphatic hydrocarbons) by selected strain was investigated. Finally, biodegradation rate of these pollutants in the presence of rhamnolipid (0.01%) and tween 80 (0.2%) was studied.
Among 40 different fungal isolates of this study, the F11 strain was selected as the superior one, base on crude oil biodegradation rate. The molecular identification showed 99.52% similarity of F11 strain to Aspergillus calidoustus. In 21 days, A. calidoustus could degrade crude oil, pyrene, and tetracosane about 54.59%, 51.43%, and 58.84%, respectively. Furthermore, crude oil, tetracosane, and pyrene biodegradation were increased to 70.97%, 79.44%, and 62.77% in the presence of rhamnolipid and to 66.78%, 74.74%, and 60.16%, in the presence of tween 80, respectively.
According to the results of this study, A. calidoustus has a great ability in biodegradation of heavy hydrocarbons. Also, it was shown that surfactants can increase the rate of hydrocarbons degradation, with much effect on aliphatic hydrocarbons, such as tetracosane, than aromatic compounds like pyrene.