Studies On Breeding Of Biosurfactant-producing Bacteria And Surface Activity Of Biosurfactant

As one kind of the natural surfactant, biosurfactants are surface-active agents which consist of both hydrophilic and hydrophobic moieties and are produced from microorganism under specific conditions. Biosurfactants has been the great interests of scientist, due to their advantages as low toxicity. biodegradability, ecological safety and structural diversity comparing with those chemical surfactants. Hence, the screening of high-yield biosurfactant strains and the optimizing of their cultivating conditions are of extensive significance in the biological and economic study.In the present paper, surface tension of fermentation broth was characterized as the main selection index, incorporating with the oil spreading method used in the screening of high-yield biosurfactant strains.16S rDNA sequence analysis technique was used to identify the strains to genus. The results of the Ionic identify experiment and TLC experiment characterized that biosurfactants produced by BS-1, BS-3, BS-4 were lipopeptide, glycolipid. phospholipid respectively, and the former two of those were anion while the last one was the cell wall addhesion. On the purpose of obtaining the best breeding condition of strains when their surface activity is highest, one-factor experimental design and orthogonal experimental design were employed to analyze the surface activity of biosurfactant. Three strains of biosurfactant-producing bacteria were isolated from environmental samples contaminated by petroleum over long range of period and were named as BS-1,BS-3,BS-4 respectively. These strains were identified as bacillus, pseudomonas and micrococcus respectively based on the results of the morphological characteristics of colony, micrograph of gram staining, and 16SrDNA sequence analysis technique. The strains reduced the surface tension of the fermentation solution from (69.0±0.2)mN/m to 27.8mN/m,27.3mN/m,26.6mN/m respectively and the mixture of the three strains named as BS-H showed highest surface activity the best stability. The optimum medium of strain BS-H generating biosurfactant was preliminary determined as:diesel oil 15ml, starch 2g, NH4NO3 1g, Na2HPO4·12H2O 1g, KH2P041g. NaCl 1g, FeSO4·7H2O 0.05g, MgSO4·7H2O 0.1g, EDTA 1g, yeast extract 0.5g, trace element 2ml, determine the volume to 1L by distilled water at initial pH 5.0,30℃. When strain BS-H was cultured under the modified conditions for 84h, the surface tension of fermentation broth was reduced from (69.0±0.2)mN/m to 21.1mN/m, and OD600 was increased from 1.723 to 2.256.While under the initial cultivating conditions, the surface tension of fermentation broth was reduced from (69.0±0.2)mN/m to 26.0mN/m. The efficiency of biosurfactant production was enhanced by 18.8%, and it indicated that the optimum conditions have the significant influence on improving the ability of strain BS-H generating biosurfactant.