The Research Of Strain Screening And Fermentation Process Of Polyether Antibiotics Lasalocid

As a class of polyketide compounds,Polyether antibiotics are mainly produced by streptomyces.Lasalocid,is a kind of commonly used polyether antibiotic obtained by fermentation of Streptomyces lasaliensis.It's commonly used to treat and prevent coccidiosis,while coccidia is difficult to produce resistance.In addition,lasalocid is widely used in aquaculture as a feed additive.At present,lasalocid has been produced industrially and used in the United States,Europe and Japan,but not yet in China.In this paper,the screening of strain and the fermentation process of lasalocid were investigated.First of all,the HPLC analysis method issued by the Ministry of Agriculture,was applied to detect the content of lasalocid in fermentation liquid,and investigated the adaptability of this method.A C18 column was used and the detection wavelength was 305 nm,the column temperature was 40 ?,the mobile phase consisted of acetonitrile,0.125mol/L ammonium acetate?adjusted pH to 4.8 ± 0.1 by phosphate?=85:15?V:V?,the flow rate was 1m L/min,sample volume was 20 ?L.The linear range,precision and resolution of the method were in line with the requirement of methodology,also it could separate the lasalocid and impurities effectively.Then,the original strain was screened through the natural screening,UV mutagenesis,resistance screening,and normal plasma mutagenesis,after rescreening,New strain's yield of Lasalocid reached 141.86 g/m L,which was about 3 times as much as that of the original strain's.Next,the process of optimizing the fermentation was carried out.In shake flask experiments,carbon and nitrogen sources,inorganic phosphate,salt,precursors of product and inoculation time and inoculation amount,initial pH,culture temperature,liquid volume were optimized by single factor experiment and the response surface optimization experiment.The optimum conditions were as follows: inoculation amount was 10%,inoculation time was 36-39 h,initial pH was 5.5,culture temperature was 26?,shaking speed was 240 r/min,liquid volume was 15 m L.The optimum concentration of each component was: soluble starch 40 g/L,pea starch 13.08 g/L,yeast extract 29.5 g/L,KH2PO₄ 8.41 g/L,MgSO₄ · 7H2 O 4 g/L,NaCl 5 g/L,methionine 0.5%.The final yield of lasalocid increased to 797.25 ?g/mL,which was 5.62 times before optimization.Finally,accroding to the results of the shake flask experiment,the amplification experiment was scaled up in a 5 L fermentor.The influences of different impeller types,stirring speed and aeration rate on fermentation were investigated.The turbo disc turbo impeller was selected.The stirring speed was 220 r/min,the aeration rate was 3.0 vvm,and the yield of lasalocid reached 1250 ?g/m L.