Effects of Crude Oil on Biomass and Protein Production by Aquatic Yeasts
Toxic effects of Bonny light crude oil on the growth of three aquatic yeasts namely Yarrowia lipolytica, Candida tropicalis and Debryomyces hansenii were studied based on their biomass and protein production. The species showed different responses to the toxic influences of various crude oil concentrations. The growth response was measured spectrophotometrically using optical density (OD) at 600nm. Yarrowia lipolytica responded positively to different crude oil levels. A general assessment indicated that 2% (v/v) crude oil concentration stimulated maximum growth and protein production of this organism. Lower yields were observed at reduced crude oil levels. Growth decreased gradually among Candida tropicalis and Debryomyces hansenii cultures in comparison to the control. Biomass of Candida tropicalis increased from 0.1 (OD600nm) at 0 h to 0.49 after 20 h at 0.5% crude oil concentration. This level gradually declined to 0.04 after 20 h cultivation at 1.5 % crude oil concentration. Maximum decline in optical density of this organism was observed at crude oil concentration of 2.0%. Protein levels for Candida tropicalis decreased from 0.13 mg/mL after 20 h at crude oil concentration of 0.5% to 0.04 mg/mL after 20 h at maximum crude oil concentration of 2%. The biomass of Debryomyces hansenii increased slightly from 0.1(OD600nm) at 0 h to 0.44 after 20 h at 0.5% crude oil level. Further decreases in OD values of this organism occurred progressively as the crude oil concentration was increased. Lowest protein yield was observed at a crude oil concentration of 2% at which the least protein production of 0.05 mg/mL was produced after 20 h.
1Nwokoro, O. and 2Chukwu, B. C. 1Industrial Microbiology and Biotechnology Laboratory, Department of Microbiology, University of Nigeria, Nsukka, Nigeria
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