Isolation and Identification of BTEX-utilizing Fungi from Soil Polluted with Petroleum hydrocarbons

Abstract

Global consumption of petroleum and petroleum products draws the public’s attention to the fate of petroleum hydrocarbons in the environment, as they can permeate the soil environment in an uncontrollable manner. This study examined the physicochemical properties of soil heavily polluted with petroleum hydrocarbons using standards methods as described by the International Soil Reference and Information Center (ISRIC). Isolation and identification of fungi was carried out using enrichment technique, cultural morphology and microscopic examination. The isolates obtained were tested for ability to utilize BTEX using mineral salts medium (MSM) supplemented with 1% v/v BTEX as the sole carbon source for 7 days. The hydrocarbon-utilizing fungal (HUF) spore counts were determined by direct counting using Neubauer Haemocytometer. The petroleum contaminated soil has a characteristic gasoline odour and black in color. The texture of the soil was observed to be sandy, with slightly alkaline pH (7.8) and a temperature of 22^oC. Moisture content (2.16%) and water holding capacity (2.07%) were found to be very low. The soil had a high content of oil and grease (1870 Mg/l), and a very high organic carbon (6.54%) and organic matter (11.28%) contents. Nitrogen (0.93%), Phosphorus (3.84 mg/kg), Potassium (2.05 mEq/100g) and Sodium (53.94 mEq/100g) were all found to be in high quantities, while Calcium (8.0 mEq/100g) and Magnesium (2.40 mEq/100g) were observed to be moderate. On the other hand, the mean heterotrophic fungal count (HFC) was found to be 3.9 ×10⁴ CFU/g and eight fungi were isolated from the soil. All fungal isolates were observed to be molds and identified as follows; Gliocladium sp., Aspergillus flavus, Aspergillus terreus DMW-3, Penicillium sp., Aspergillus terreus DMW-5, Trichoderma sp., Aspergillus terreus DMW-7 and Aspergillus niger. The highest percentage increase in hydrocarbon-utilizing fungal (HUF) spore counts was observed with Aspergillus terreus DMW-5 (98.4%) and Gliocladium sp. (98.1%) while the lowest percentage increase in hydrocarbon utilizing fungi was observed with Aspergillus flavus (94%). From the findings in this study, it appears that petroleum pollution did not inhibit the growth and variation of fungi in petroleum-contaminated soil. It seems that the fungi used petroleum hydrocarbons as nutrient.