Isolation and screening of biosurfactant producing yeast from soil contaminated with oil

Abstract

The present study was aimed to isolate yeasts from soil samples contaminated with oil and their ability to produce biosurfactants. Five samples were collected from different sites of Baghdad, thirty four isolate of yeasts were obtained from these contaminated soil. Nineteen isolates from them were able to produce biosurfactant according to the diameter of clearing zonein solution test, while other isolates gave negative results. The yeast isolates which gave positive result werequantitatively screened on the basis of emulsification index and surface tension, secondary screening showed that isolates SD5, SB8 and SK10 giving the highest yield of biosurfactant in their cultures and the values of emulsification index were 45.7%, 56.9% and 53.4% respectively. Also, the biosurfactant of isolates SD5, SB8 and SK10 were exhibited maximum ability to reduce the surface tension of medium to 38.2, 27.1 and 30.8 mN\m respectively. Finally selected isolates SD5, SB8 and SK10 were identification on the basis of morphological and biochemical tests, the results revealed that isolates were identified as Saccharomyces cerevisiaeSB8, Candida glabrataSD5 and Candida glabrata SK10 respectively.The three most active isolates were tested to see their ability to produce biosurfactant in BH medium supplemented with four types of agricultural residues (rice bran, banana peel, wheat bran and corn cobs) as a source of carbon compared with BH medium with glucose. All isolates showed good ability to produce biosurfactant in liquid medium with different types of agricultural wastes and also with glucose. Candida glabrata SD5 exhibited highest activity for biosurfactant production when grown on agricultural wastes and glucose depend on the values of emulsification index and surface tension, whilethe wheat bran as a substrate gave best stimulation for biosurfactant production compared with other agricultural wastes.