Fermentation Conditions And Products Characteristic Of Biosurfactant-Producing Bacterium

Biosurfactants have the characteristics of reducing the surface tension, low toxicity and biodegradability. Biosurfactants can be widely applied in oil exploitation, food industry and medical fields. In the present study, a biosurfactant-producing bacterium DGG-1-3-F was identified. The effect of carbon sources and environmental conditions on biosurfactant production, the separation of biosurfactant and its properties were investigated.The strain DGG-1-3-F was confirmed as Bacillus licheniformis by morphological,physiological and biochemical, 16 S rDNA sequences and the cellular fatty acids.The results showed that the strain was able to grow and produce biosurfactants with glucose, fructose, galactose, xylose, sucrose, maltose, lactose, dextrin and soluble starch as carbon sources. The maximum growth was achieved when soluble starch was used as carbon source and the lowest surface tension of the fermentation supernatant was 22.6 mN/m with dextrin as carbon source. The strain could grow and produce biosurfactant at 20-50 o C,initial pH 6.0-12.0 and 0-8% NaCl concentration while only grow at 9-11% NaCl concentration. The maximum growth was obtained at 40 oC, initial pH 8.0 and 0% NaCl concentration, respectively. The lowest surface tension of the cell-free broth was 22.1 mN/m at 50 oC, 22.4 mN/m at pH 7.0 and 22.4 mN/m at 0% NaCl concentration, respectively.The biosurfactant obtained by acid precipitation and methanol extraction from the fermentation supernatant was confirmed to be anionic polysaccharide biosurfactant by the charge and TLC analysis. The biosurfactant showed emulsification activity against n-hexane,tridecane, liquid paraffin, toluene, motor oil, soybean oil, corn oil and peanut oil. The highest emulsification index was recorded with tridecane(55%), followed by the emulsification index with liquid paraffin and soybean were 50% and 48%, respectively. The lowest emulsification index was only 4% with corn oil. The critical micelle concentration(CMC) of the biosurfactant was 100 mg/L. The biosurfactant showed good foamability and the foam was totally disappeared at 7.5 h. The biosurfactant of 2-10 mg/mL displayed significant inhibition on Escherichia coli. The biosurfactant of 5-10 mg/mL displayed significant inhibition on Pseudomonas aeruginosa PAOL, Bacillus subtilis, Erwinia chrysantheme Echool andStaphylococcus aureus while Mycobacterium avium MgCo could only be inhibited by 10mg/mL biosurfactant solution. The surface tension of biosurfactant remained stable at-20-115 oC, pH 6.0-13.0 and 0-7% NaCl. The emulsification index remained stable at-20-40 oC,pH6.0-13.0 and 0-2% NaCl. The emulsification activity was decreased with increasing the dilution of biosurfactant concentration.The oil removal efficiency from the contaminated sand by the fermentation supernatant and biosurfactant solution reached about 83.00% and 42.00% at 200 rpm, respectively. The fermentation supernatant could remove 20.84% and 14.30% soybean oil from cotton cloth and dacron cloth, respectively. The biosurfactant solution could remove 46.06% and 24.66%soybean oil from cotton cloth and dacron cloth, respectively.