Screening Of Biosurfactant-producing Bacterial Strains

Biosurfactants are a kind of good surface-active compounds mainly synthesized bymicroorganisms, with both hydrophilic and hydrophobic moieties. Compared withchemical surfactants, Biosurfactants have distinct advantages like no toxicity, higherbiodegrade ability and friendly to environment. Recently, Biosurfactants are widelyused in the fields of crude oil recovery, environmental protection, food and medicine.The paper mainly includes the screening and identification of biosurfactant-producingbacteria, the identification, components analysis and the physicochemical properties ofthe metabolites, the optimization of culture conditions for shaking flask fermentation ofthe strain. The main resuits are as follows:With crude oil as the sole carbon source, sampling in the oil contaminatedenvironment,6strains with better ability of emulsification were selected throughpreliminary screening. The strain BS8-17with the most ability of surface activity hadbeen selected from the6bacterias by the screening method of oil displacement activityassay. According to the following identifications of colony morphology, cellmorphology, physiological and biochemical properties of bacteria and16S rDNA genesequence analysis, the strain BS8-17was closely related to the genus Bacillus subtilis,named Bacillus subtilis BS8-17.The reducing sugar did not exist in the measured by DNS colorimetry, whichindicated that the surface-active compounds produced by strain BS8-17was notglycolipid. The result of electric charge measurement showed the product was anionicbiosurfactant. Analysed by TLC and FTIR, it was demonstrated the surface-activecompound synthesized by strain BS8-17was lipopeptide. Through the research ofstability of biosuifactants and emulsifying ability, it was shown that lipopeptide had agood tolerability to temperature, pH and salt. The surfactants had a good emulsionstability to kerosene.The fermentation conditions and culture mediums of lipopeptide production bystrain BS8-17were optimized by single-factor experiment. The better fermentationconditions for lipopeptide production were as follows: temperature37℃, initial pH8.0,seed age12h, the quantity of inoculation3%, volume in shake flask35mL/250mL,rotation speed of rocking bed180r/min, and culture time96h. The better culturemediums for lipopeptide production were as follows(g/L): glycerol25,(NH4)2SO42.5, KH2PO44, Na2HPO44,MgSO40.5. Under the better culture environment, thelipopeptide yield of strain BS8-17was1158mg/L, and the output had increased by70%compared with the initial.