Document Type : Research Paper
Authors
1 Former M. Sc. student, Department of Plant protection, Faculty of Agriculture, Shahid Chamran University of Ahvaz, Iran.
2 Associate Professor, Department of Plant protection, Faculty of Agriculture, Shahid Chamran University of Ahvaz, Iran.
3 Ph.D. in Mycology and Plant Pathology, Department of Plant protection, Faculty of Agriculture, Shahid Chamran University of Ahvaz, Iran.
Abstract
Introduction: Soil contamination by crude oil is common in oilfield in different processes including extraction, transfer and refining of crude oil and its products. Bioremediation is an interesting strategy to remediation of soils polluted with crude oils and its derivatives. This method is based on the employed of organisms to neutralize oils in the environment. During bioremediation process, microorganisms degrade and transform persistent crude oil hydrocarbons into simple and less persistent molecules. It is very important to identify the microorganisms that can utilize and degrade these pollutants. Generally, fungi play an essential role in the biodegrading and remediation of soils polluted with hydrocarbons. Therefore, the present study was carried out to evaluate the tolerance of the fungal isolates obtained from the oil-contaminated soil to crude oil in Maroon oilfield.
Materials and Methods Twenty-three fungal isolates belonging to 12 genera were used to investigate their toleration to crude oil. The fungi had been isolated in December 2016 from soil samples contaminated with crude oils from four sites in the maroon oilfield of Ahwaz. The fungal isolates were obtained from the fungal collection of the department of plant protection of shahid chamran university of Ahvaz. The fungi had been identified based on phylogenetic analysis and morphological characteristics. The tolerance of these fungi to crude oil was studied by growing them on PDA medium containing 30, 40, and 50% concentrations of crude oil and through Radial growth measurements. The tolerance to crude oil was calculated based on growth inhibition percentage of fungal isolates. The research was conducted in a factorial completely randomized design for analysis of the growth-inhibitory percentages.Three replications were performed for each control (PDA-Tween culture medium without crude oil) and treatment. Mean data comparisons were performed based on Duncan's multi-range method at 1% significance level (P<0.01), using SAS 9.1 software.
Results and Discussion: All isolates grew in the culture medium containing different concentrations of crude oil. The results of variance analysis showed significant difference between the main effects of isolates and different levels of crude oil, as well as their interaction effects on growth inhibition (P< 0.01). The growth inhibition means of three concentrations of 50, 40, and 30% was 33.6, 26.1, and 21.4, respectively, which indicated the direct relationship between the concentration level and the growth inhibition percentage. Naturally crude oil is a heterogeneous mixture that composed of hydrocarbons compounds, sulfur and other heavy elements, therefore an increase in its concentration leads to an addition in its toxicity. Comparisons of the mean of growth inhibition in different isolates in response to crude oil concentrations demonstrated that Aspergillus sp. SCUA-Deh-3 with 65.1 inhibition growth and placed in the group a had the lowest growth ability and highest sensitivity to oil and statistically significant difference exists between this isolate and all fungi (P< 0.01). M. circinelloides SCUA-34 and Cladosporium puyae SCUA-m5f4 ranked next with 45.1 and 41.8 inhibition of growth respectively and were placed in group b. Alternaria destruens SCUA-Deh-1 and Aspergillus sp.SCUA with 5.05 and 6.5 inhibitions and placed in group M had the lowest sensitivity and inhibition and had significant difference with all other fungi (P> 0.01). Also, the growth rate of both used Alternaria isolates enhanced by increasing oil concentration in media. The growth inhibition means were equal only in two isolates, Penicillium chrysogenum SCUA-Deh-12 and Aspergillus sp. SCUA-m1f8r2, in two concentrations of 30 and 40 % (4.6 and 19.6, respectively). Also, Aspergillus sp. SCUA-m3f10 had equal means percent inhibition of growth in two concentrations of 40 and 50 (28.5). Furthermore, in the isolates of Aspergillus sp. SCUA-Deh-3 initially stimulated growth at 40% concentration and then the growth inhibition percentage increased at concentration of 50%.
Conclusion: These results showed that Alternaria destruens SCUA-Deh-1 and Aspergillus sp. SCUA-m1f7r2 have more growth potential than other fungi at presence of crude oil in growth medium. Also, the growth inhibition of Alternaria decreased by increasing of crude oil concentration. In other words, these two isolates were considered the most tolerant isolates to crude oil. So it seems; these native isolates are among the best fungi for bioremediation of oil-contaminated soils. However, regarding the biological degradation of petroleum materials, it seems necessary to mention that physicochemical properties and bioavailability of hydrocarbon pollutants play an important roles in their bioremediation.
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