氧载体对L—天冬酰胺酶发酵过程影响的研究

以抗癌药物Ｌ天冬酰胺酶生产为应用背景,针对发酵过程中存在严重耗氧问题,研究了氧载体对发酵过程的影响。通过对几种氧载体的筛选,认为正十二烷最适合于该发酵过程。随后以产物Ｌ天冬酰胺酶活性、菌体浓度以及溶氧水平为主要指标,考察了氧载体在发酵过程中的作用,实验表明,发酵基质中５％正十二烷的添加量为最佳浓度,这种氧载体的加入,明显地提高了发酵介质中的溶氧水平,改善了供氧条件,增加了菌体浓度,提高了Ｌ天冬酰胺酶发酵水平,在优化条件下,可使发酵液最终酶活提高２１％左右     

黄单胞杆菌XC—82,R5二步发酵工艺研究

通过对黄单胞杆菌ＸＣ－８２,Ｒ５株的黄原胶二步发酵工艺研究,针对菌株在生长时期与产胶时期不同培养条件的需求,确定了两个阶段各自适宜的培养基组成,温度,ｐＨ值条件,实验表明,当流加稀释率为５时,二步发酵生产可达到了较高水平,其产胶量较传统的间歇发酵提高３１％。     

溶氧控制策略对结冷胶发酵过程的影响

结冷胶作为一种吸水水性极强的胶体,其广泛应用于食品,饮料,医药,化妆品等行业。发酵法生产结冷胶的过程中,由于发酵液的黏度很高,溶解氧(DO)的控制极为困难。大规模工业化生产结冷胶的过程中,通常可以通过增加通气量或提高搅拌转速这两种策略来提高发酵过程中的溶氧水平。本文通过对比这两种控制策略对60吨发酵罐生产结冷胶产量、能耗的影响,得出通过提高搅拌转速的溶氧控制策略更加高效和节能。提高搅拌转速的发酵批次与增加通气量的发酵批次相比,结冷胶平均产量提高了9%,能耗降低了10%。     

结合于GATA元件的Ⅳ型锌指蛋白

至今已发现了四种锌指蛋白（Ｚｆｐ）。Ⅰ型为Ｃｙｓ－Ｘ２－４－Ｃｙｓ－Ｘ３－Ｐｈｅ－Ｘ５－Ｌｅｕ－Ｘ２－Ｈｉｓ－Ｘ３－Ｈｉｓ,简写Ｃ２Ｈ２。ＴＦⅢＡ为Ｃ２Ｈ２×９,即９个锌指的重复单位。Ｓｐ１为Ｃ２Ｈ２×３。目前已发现有１０００种以上具有Ⅰ型锌指同源保...     

高粘发酵体系不同搅拌桨的CFD模拟及发酵验证

搅拌桨是高好氧高黏度微生物发酵实现高效反应必不可少的因素之一,不同搅拌桨组合对发酵过程的影响十分重要。威兰胶是由产碱杆菌在高耗氧高粘度发酵体系下合成的胞外微生物多糖,广泛应用于水泥、石油、油墨、食品等行业中。本研究借助于计算流体力学(Computational fluid dynamics,CFD)的方法,以威兰胶发酵液体系为研究体系,研究了6种不同搅拌桨组合在反应器内流体速率分布、剪切速率、和气含率等参数。将模拟效果较好的3种组合用于威兰胶发酵过程。研究表明MB-4-6搅拌桨组合对改善发酵罐内部的溶氧及流场分布效果最明显,威兰胶产量水平提高了13%。同时在该组合下威兰胶的产品粘度得到有效提高。     

XCCNAU-92生产黄原胶的工业发酵培养基成份

ＸＣＣＮＡＵ－９２生产黄原胶的工业发酵培养基成份是：蔗糖、玉米淀粉、氮源Ｘ、鱼粉、ＣａＣＯ３、ＭｇＳＯ４、Ｋ２ＨＰＯ４。适宜的Ｃ／Ｎ是：蔗糖（玉米淀粉）／氮源Ｘ＝６０．０／１．０,蔗糖（玉米淀粉）／鱼粉＝６０．０／１０．０。ＣａＣＯ３、ＭｇＳＯ４对ＸＣＣＮＡＵ－９２合成黄原胶有明显促进作用,Ｋ２ＨＰＯ４在发酵过程中使ｐＨ保持稳定,Ｍｎ２＋、Ｚｎ２＋、Ｆｅ３＋、柠檬酸和谷氨酸对生产黄原胶无促进作用。     

氧载体对L-天冬酰胺酶发酵过程影响的研究

以抗癌药物L－天冬酰胺酶生产为应用背景,针对发酵过程中存在严重耗氧问题,研究了氧载体对发酵过程的影响。通过对几种氧载体的筛选,认为正十二烷最适合于该发酵过程。随后以产物L－天冬酰胺酶活性、菌体浓度以及溶氧水平为主要指标,考察了氧载体在发酵过程中的作用．实验表明,发酵基质中5％正十二烷的添加量为最佳浓度,这种氧载体的加入,明显地提高了发酵介质中的溶氧水平,改善了供氧条件,增加了菌体浓度,提高了L－天冬酰胺酶发酵水平,在优化条件下,可使发酵液最终酶活提高21％左右。     

谷氨酸发酵溶氧变化的初步观察

在需氧的工业发酵过程中,培养液中溶氧量的高低对微生物的活动以及发酵产物的积累具有重要作用。谷氨酸发酵中,溶氧水平对谷氨酸蓄积的影响也有人作了一些研究,据Hirose等的报告指出,在适宜的溶氧条件(氧传递速度10.5×10~(-7)克分子氧/毫升/分/1     

利用Tn5gusA5对大豆慢生根瘤菌lrp基因的诱变

通过对重组质粒ｐＧＸＮ３００中的 ２．３ｋｂ ＥｃｏＲＩ片段测序分析发现,其上有一完整的ｌｒｐ基因和部分 ｐｕｔＡ基因,与 Ｋｉｎｇ ＮＤ等［１］报道的 Ｂ．ｊａｐｏｎｉｃｕｍ的ｌｒｐ基因ＤＮＡ序列有 ８８％同源性。利用 Ｔｎ５ ｇｕｓＡ５定位 诱变方法,对质粒ｐＧＸＮ３００进行插入诱变,得到２．３ｋｂ　ＥｃｏＲＩ片段上有Ｔｎ５ｇｕｓＡ５插入位点的质粒ｐＧＸＮ３００－ Ｔ３８,将ｐＧＸＮ３００－Ｔ３８转移到大豆馒生根瘤苗（Ｂ．ｊａｐｏｎｉｃｕｍ）ＧＸ２０１中,得到的ＧＸ２０１转移接合子与不相容 质粒ｐＰＨ１ＪＩ发生同源双交换。通过抗性及ｇｕｓＡ活性检测,筛选到一ｌｒｐ基因突变株。Ｓｏｕｔｈｅｍ杂交分析证 明这突变株的 Ｔｎ５ ｇｕｓＡ５插入确实是同源交换而不是转座产生,表明 Ｔｎ５ ｇｕｓＡ５ 诱变可以应用于大豆慢生根 瘤菌中的突变林筛选。     

紫云英汁液单细胞蛋白发酵工艺研究

紫云英汁液含有１０％的糖和２．６６％的有机氮化物,稀释成５倍后,以假丝酵母Ｃａｎｄｉｄａ ａｒｂｏｒｏ Ａｓ２．５６６为生产菌进行单细胞蛋白发酵,通过单因素搜索和正交试验对发酵工艺进行了优化,结果表明：较优培养基为初糖２．５％、酵母粉０．１５％、ＫＨ２Ｐ０Ｒ０．２％、ＭｇＳＯ４、０．０５％,初始ｐＨ值＝５,发酵温度３０℃,接种量５％。在２Ｌ发酵罐中验证,酵母浓度最高达１０．５３ｇ干重／Ｌ,基质生长     

Hydrogen peroxide (H<Subscript>2</Subscript>O<Subscript>2</Subscript>) supply significantly improves xanthan gum production mediated by <Emphasis Type="Italic">Xanthomonas campestris</Emphasis> in vitro

To improve xanthan gum productivity, a strategy of adding hydrogen peroxide (H₂O₂) was studied. The method could intensify oxygen supply through degradation of H₂O₂ to oxygen (O₂). In shake flask testing, the xanthan gum yield reached 2.8% (improved by 39.4%) when adding 12.5 mM H₂O₂ after 24 h of fermentation. In fermentor testing, it was obvious that the oxygen conditions varied with the H₂O₂ addition time. Eventually, gum yield of 4.2% (w/w) was achieved (increased by 27.3%). Compared with the method of intense mixing and increasing the air flow rate, adding H₂O₂ to improve the dissolved oxygen concentration was more effective and much better. Moreover, addition of H₂O₂ improved the quality of xanthan gum; the pyruvate content of xanthan was 4.4% (w/w), higher than that of the control (3.2%).     

Xanthan gum production under several operational conditions: molecular structure and rheological properties*

Xanthan gum production under several operational conditions has been studied. Temperature, initial nitrogen concentration and oxygen mass transfer rate have been changed and average molecular weight, pyruvilation and acetylation degree of xanthan produced have been measured in order to know the influence of these variables on the synthesised xanthan molecular structure. Also, xanthan gum solution viscosity has been measured, and rheological properties of the solutions have been related to molecular structure and operational conditions. The Casson model has been employed to describe the rheological behaviour. The parameter values of the Casson model, tau(0) and K(c), have been obtained for each polysaccharide synthesised under different operational conditions. Both pyruvilation and acetylation degrees and average molecular weight of xanthan increase with fermentation time at any operating conditions. Xanthan molecules with the highest average molecular weight have been obtained at 25 degrees C. Nevertheless, at this temperature acetate and pyruvate radical concentration are lowest. Nitrogen concentration in broth does not show any clear influence over xanthan average molecular weight, although with high nitrogen source concentration xanthan with low pyruvilation degree is produced.     

The anomaly of oxygen diffusion in aqueous xanthan solutions

A membrane-covered polarographic oxygen electrode was used to measure oxygen diffusion coefficients in aqueous polyelectrolyte solutions of xanthan gum, sodium alginate, and sodium carboxymethylcellulose (CMC). In sodium alginate solutions, dilute xanthan solutions, and solutions containing more than 0.3 wt % CMC, oxygen diffusion coefficients decrease with increasing polymer concentrations. Interestingly, in dilute CMC solutions and concentrate xanthan solutions containing more than 0.5 wt % xanthan gum, oxygen diffusion coefficients increase with increasing polymer concentrations, and values exceeding that in pure water are generally observed.     

Direct utilization of lactose in clarified cheese whey for xanthan gum synthesis byXanthomonas campestris

Summary A derivative ofXanthomonas campestris B1459 was constructed that utilizes lactose in clarified cheese whey for xanthan gum synthesis. Genes conferring lactose utilization carried by transposon Tn951 were inserted into the bacterial chromosome. The ability to use lactose for xanthan gum synthesis was stably inherited and the amount of xanthan produced suggested carbohydrate conversion efficiencies similar to wild-typeX. campestris growing in the presence of glucose. Bench-scale fermentation of this organism and identification of the optimal whey sources and pretreatments can now proceed.     

Sources and methods of manufacturing xanthan by fermentation of various carbon sources

Xanthan gum, an anionic polysaccharide with an exceptionally high molecular weight, is produced by the bacterium Xanthomonas sp. It is a versatile compound that has been utilized in various industries for decades. Xanthan gum was the second exopolysaccharide to be commercially produced, following dextran. In 1969, the US Food and Drug Administration (FDA) approved xanthan gum for use in the food and pharmaceutical industries. The food industry values xanthan gum for its exceptional rheological properties, which make it a popular thickening agent in many products. Meanwhile, the cosmetics industry capitalizes on xanthan gum's ability to form stable emulsions. The industrial production process of xanthan gum involves fermenting Xanthomonas in a medium that contains glucose, sucrose, starch, etc. as a substrate and other necessary nutrients to facilitate growth. This is achieved through batch fermentation under optimal conditions. However, the increasing costs of glucose in recent years have made the production of xanthan economically unviable. Therefore, many researchers have investigated alternative, cost-effective substrates for xanthan production, using various modified and unmodified raw materials. The objective of this analysis is to investigate how utilizing different raw materials can improve the cost-efficient production of xanthan gum.     

Effects of temperature on cell growth and xanthan production in batch cultures of Xanthomonas campestris

Batch xanthan fermentations by Xanthomonas campestris NRRL B-1459 at various temperatures ranging between 22 degrees C and 35 degrees C were studied. At 24 degrees C or lower, xanthan formation lagged significantly behind cell growth, resembling typical secondary metabolism. However, at 27 degrees C and higher, xanthan biosynthesis followed cell growth from the beginning of the exponential phase and continued into the stationary phase. Cell growth at 35 degrees C was very slow; the specific growth rate was near zero. The specific growth rate had a maximum value of 0.26 h(-1) at temperatures between 27 degrees C and 31 degrees C. Cell yield decreased from 0.53 g/g glucose at 22 degrees C to 0.28 g/g glucose at 33 degrees C, whereas xanthan yield increased from 54% at 22 degrees C to 90% at 33 degrees C. The specific xanthan formation rate also increased with increasing temperature. The pyruvate content of xanthan produced at various temperatures ranged between 1.9% and 4.5%, with the maximum occurring between 27 degrees C and 30 degrees C. These results suggest that the optimal temperatures for cell growth are between 24 degrees C and 27 degrees C, whereas those for xanthan formation are between 30 degrees C and 33 degrees C. For single-stage batch fermentation, the optimal temperature for xanthan fermentation is thus dependent on the design criteria (i. e., fermentation rate, xanthan yield, and gum qualities). However, a two-stage fermentation process with temperature shift-up from 27 degrees C to 32 degrees C is suggested to optimize both cell growth and xanthan formation, respectively, at each stage, and thus to improve overall xanthan fermentation.     

Preservation of Xanthomonas campestris on agar slopes: effects on xanthan production

Xanthomonas campestris NRRL B-1459 and a variant E2, when preserved on agar slopes (transferred monthly) over 11 months did not deteriorate in their ability to produce xanthan in quantity and quality, as determined by culture in 500-ml baffled flasks. Variations between 8 and 14% (with respect to the average) in the final xanthan concentration were observed for the E2 and B-1459 strains, respectively. A wide range of final viscosities was obtained; these were consistent with the changes in gum concentration. Differences were more likely associated with differences in fermentation kinetics rather than being inherent to the strains. The rheological quality of both polysacharides was relatively constant throughout the time of culture maintenance. Preservation of these bacteria on agar slopes was an adequate method, in contrast to previous reports. In the period studied, strain E2 produced higher gum titres and slightly lower gum quality compared to strain B-1459. Correspondence to: E. Galindo     

Xanthan biopolymer production at increase concentration by pH control

Efficient production of xanthan gum by fermentation with Xanthomonas campestris NRRL B-1459 can be accomplished at concentrations of xanthan in the fermented broth > 3%. This level of more than twice that previously attained by us results from continuously controlling the fermentation pH with alkali. Only a slight decrease in fermentation rate and yield occurs. When ammonia is used for pH control, cell production more than doubles and fermentation time is shortened. However, xanthan yield is decreased by the diversion of additional sugar to growth.