用十二烷基硫酸钠消除枯草芽孢杆菌中的质粒

为获得宿主菌 ,研究了十二烷基硫酸钠 (SDS)对枯草芽孢杆菌中质粒的消除 .将过夜培养的枯草芽孢杆菌2 4/pMX45接种于含SDS( 0— 0 .0 0 8% )的LB培养基中 ,当SDS浓度 (w /v)大于或等于 0 .0 0 6 %时 ,菌体不能生长 .SDS的亚致死浓度为 0 .0 0 5 % ,其致死率达 99% .菌液稀释后涂LB平板 ,再随机挑选单菌落至抗性平板 ,检测由质粒编码的红霉素抗性是否丢失 .氯化铯 溴化乙锭梯度离心及质粒DNA的电泳图像证实了 2 4/pMX45的衍生菌株A7中的质粒已完全被消除 .A7延迟期较短 ,并且细胞浓度高于 2 4/pMX45 .用SDS处理 8h后 ,2 4/pMX45的遗传标记开始丢失 ,消除率持续增高至 2 2h ,随之消除质粒的菌体量保持恒定 .在未经SDS处理的对照实验中 ,相同条件下培养 2 4h及 48h后 ,没有发现质粒自然丢失的现象 ,因此SDS能消除枯草芽孢杆菌中的质粒     

Optimization of Riboflavin Production from ccpA Mutant Bacillus subtilis 24A1/pMX45

Bacillus subtilisis widely used for the productionof vitamins and other products including industrial en-zymes such as amylases, proteases and lipase. Butsyntheses of those products are repressed by the pres-ence of glucose, which is viewed as carbon catabolicrepression (CCR). InBacillus subtilis,CCR is main-ly mediated by the global regulator protein CcpAwhich was encoded byccpAgene[1]. It is therefore of crucial importance to relievingCCR ofBacillus subtilisfor industrial production. I…     

Enrichment of semi-volatile organic acids from aqueous solutions by multiple-effect membrane distillation

Multiple-effect membrane distillation(MEMD) process for enriching semi-volatile organic acids from their individual aqueous solutions was performed by using a hollow fiber-based air gap membrane distillation(AGMD)module with the function of internal heat recovery.Aqueous solutions of glyoxylic acid,glycolic acid,lactic acid,pyruvic acid,malonic acid and glutaric acid were used as model feed.For a feed of 1%(mass fraction),each acid could be enriched for 8-20 times,which depended on the surface tension of the concentrate.The operation performance of MEMD process was characterized by permeation flux J,performance ratio PR and acid rejection rate R.The effects of cold feed-in temperature,heated feed-in temperature,feed-in volumetric flow rate and feed-in concentration on MEMD performance were experimentally evaluated.Maximum values of J,PR and R were 4.8 L/(h·m 2),9.84 and 99.93%,respectively.Moreover,MEMD process demonstrated a fairly good stability in a long-term experiment lasting for 30 d when aqueous solution of 4%(mass fraction) lactic acid was used as a feed.