灵芝三萜酸分批发酵的非结构动力学模型

研究了灵芝胞内和胞外三萜酸在30L发酵罐中分批发酵的动力学特征。利用Sigmoid函数构建了灵芝细胞生长、底物消耗、胞内和胞外三萜酸的非结构动力学模型,并根据Boltzmann拟合求解出各模型参数。结果表明,各模型预测值能够较好地吻合实验实测值。灵芝细胞比生长速率在第2.5天达到最大值（μmax）,为0.700d?1;葡萄糖比消耗速率在第2.4天达到最大值（qS, max）为1.060d?1;胞内三萜酸比合成速率在第4.7天达到最大值（qITA, max）为11.345mg/(g·d);胞外三萜酸比合成速     

黑曲霉产糖化酶黑箱模型的构建和应用

利用碳限制恒化实验研究了黑曲霉生长和糖化酶生产之间的相关性,结果表明当比生长速率低于0.068 h–1时,菌体生长与产酶是相关的,当比生长速率大于0.068 h–1时,菌体生长与产酶不相关。根据恒化实验结果获得黑曲霉葡萄糖底物消耗的Monod动力学模型,并结合葡萄糖和氧消耗的Herbert-Pirt方程和产物形成的Luedeking-Piret方程构建黑曲霉产糖化酶的黑箱模型。应用该模型设计指数补料分批发酵实验控制菌体比生长速率在0.05 h–1,使糖化酶的得率最高达到0.127 g糖化酶/g葡萄糖,并成功地使用模型描述了黑曲霉产糖化酶的发酵过程。实验值和模拟值进行比较表现出很好的适用性,表明黑箱模型可以用于指导黑曲霉产糖化酶发酵过程的设计和优化。     

层生镰孢菌产甲壳素脱乙酰酶发酵动力学

对层生镰孢菌产甲壳素脱乙酰酶的发酵动力学进行了研究。通过Logistic方程分别构建层生镰孢菌细胞生长、甲壳素脱乙酰酶（CDA）合成及糖基质消耗的非结构动力学模型,并利用1stOpt软件对该模型进行了模拟,采用Origin8.0软件得到了非线性曲线拟合图形及各模型参数。结果表明,各模型预测值与实验数据能较好地拟合,层生镰孢菌细胞的比生长速率在第15.52h达到峰值（μ_{m, x}）0.160h^-1;层生镰孢菌的底物比消耗速率在26.51h时达到峰值（μ_{m, s}）0.096h^-1;层生镰孢菌的甲壳素脱乙酰酶比合成速率19.40h达到峰值（μ_{m, p}）0.548U/(mL·h)。模型拟合和实验数据具有良好的适应性,基本上反映了层生镰孢菌发酵产酶过程的动力学特征,为今后的工业化规模生产提供理论依据。     

Kitasatospora sp. MY5-36产ε-聚赖氨酸分批补料发酵动力学

以北里孢菌(Kitasatospora sp.)MY 5-36为供试菌株,对ε-聚赖氨酸分批补料发酵动力学模型进行研究。建立了该菌株发酵合成ε-聚赖氨酸的菌体生长、产物合成和总糖消耗的动力学模型,并通过Origin 8.1软件对模型参数进行非线性拟合。结果表明:菌体量和聚赖氨酸的产量分别为16.25和13.15 g/L,产物合成与菌体生长的关系为部分耦联型。经验证,预测值与实验值有良好的拟合性,拟合度分别为0.999、0.995和0.992,说明所构建模型能够较好地反映ε-聚赖氨酸分批补料发酵过程。     

重组大肠杆菌高密度发酵产甲羟戊酸动力学

为提高甲羟戊酸产量,探究其发酵生产规律,以重组大肠杆菌YJM16为供试菌株,进行5 L发酵罐匀速补料的高密度发酵实验,最终细胞产量达到54.48 g/L,甲羟戊酸产量达到40.43 g/L,产率为20.2%。然后根据Logistic方程、Luedeking-Piret方程和类似Luedeking-Piret方程,拟合出重组大肠杆菌高密度发酵过程中菌体生长、甲羟戊酸合成、基质消耗的动力学模型及模型参数。结果表明,甲羟戊酸的合成与重组大肠杆菌的生长速率及菌体积累量均有关。菌体生长、底物消耗模型和产物形成模型拟合度R2分别达到了0.931 9、0.957 8和0.975 1,可用于描述利用重组大肠杆菌高密度发酵生产甲羟戊酸过程。     

蛹虫草多糖和D-甘露醇深层发酵的非结构动力学模型

多糖和D-甘露醇是蛹虫草的重要药理活性成分。本文开展了蛹虫草在分批发酵过程中同时生产多糖和D-甘露醇的发酵动力学研究。利用Sigmoid函数构建了蛹虫草菌丝生长、糖基质消耗、多糖和D-甘露醇的非结构动力学模型,并根据Boltzmann方程拟合求解出各模型参数。结果显示,各模型的实测值和预测值拟合度较好。蛹虫草比生长速率在第1.0天达到最大值（μ_max）1.244d^-1;底物葡萄糖的比消耗速率在第0.6天达到最大值（q_{S, max}）2.163d^-1;多糖比合成速率在第2.0天达到最大值（q_{P, max}）51.852mg/(g·d);D-甘露醇比合成速率在第0.99天左右达到最大值（q_{D, max}）37.963mg/(g·d)。蛹虫草多糖的形成与菌丝细胞的生长呈现部分生长关联型,而D-甘露醇的形成与细胞生长呈现生长关联型关系。研究结果为利用分批发酵规模化同时发酵生产蛹虫草多糖和D-甘露醇提供了理论依据。     

通气量对灵芝菌丝体液态深层发酵合成灵芝三萜的影响

采用5 L搅拌式发酵罐研究灵芝菌丝体液态深层发酵合成灵芝三萜的扩大培养条件,考察了不同条件下的通气量对灵芝菌丝体生长、比生长速率、灵芝三萜合成、比合成速率、还原糖消耗、还原糖比消耗速率、铵根离子消耗以及铵根离子比消耗速率的影响。研究结果表明,通气量能够显著影响菌丝体的生长以及灵芝三萜的合成,当通气量为8 L/min时,菌丝体合成灵芝三萜得率和生产强度最高,分别为0.204 g/L和0.00131 g/(L·h),最大菌丝体得率达到8.77 g/L。发酵过程中菌丝体最大比生长速率为0.0704 1/h,灵芝三萜最大比合成速率为0.0256 1/h,还原糖和铵根离子最大比消耗速率分别为0.562 1/h和0.0171 1/h。     

金针菇在淀粉工业废水中发酵的生理生化特性

以经液化处理的淀粉工业废水作金针菇液体深层发酵的培养基,研究发酵过程中菌球形态、生物量、pH总糖、还原糖、氨态氮、糖化酶、蛋白酶的变化规律,描述了菌体的生长曲线,得到了菌丝体生长的动力学模型。第1～2d为延滞期,第3～8d为快速生长期,第8d后为衰老期。其中第3～6d菌丝体生长最为迅速,酶活力最高,基质消耗最快。发酵过程中pH呈上升趋势。对生理生化各因子之间的相互关系作了讨论。     

3-羟基丙酸分批发酵过程中的pH控制策略研究

本文利用重组大肠杆菌以甘油为底物发酵合成3．羟基丙酸,考察了不同pH对3．羟基丙酸产量及菌体生长的影响,发现在pH6．5条件下,细胞比生长速率达到最大值,延迟期也相对较短;而pH7．0有利于3-羟基丙酸的合成,控制pH7．0可以使3-羟基丙酸产量达到7．39g／L。基于不同pH条件下对细胞比生长速率和3-羟基丙酸比生成速率的分析,提出3．羟基丙酸分批发酵过程中的pH控制策略,即在发酵过程前5h将pH控制在6．5,5h～15h控制pH为7．0,此时有利于细胞生长;而后在15h-25h控制pH为7．5,25h后控制pH为7．0,从而使细胞具有较高的3．羟基丙酸比合成速率。在此控制策略下经过34h发酵3-羟基丙酸的终产量达到8．76g／L,比pH7．0条件下的3-羟基丙酸产量提高了18．54％。     

药用蕈菌紫芝液体培养的生长特征分析

使用专门设计的ALR ff蕈菌液体培养反应器 ,研究了有关紫芝液体培养过程中菌丝生长的特征。结果表明 ,液体培养时紫芝菌丝生长对温度有较宽的适应范围 2 5℃～ 3 5℃ ,但生长比速率相差很大。通气量由 0 93vvm提高到 1 6 4vvm时 ,菌丝生长比速率明显地增加 ,最大值为 0 0 4 4 4 (h- 1) ;当通气量进一步提高到 2 5 0vvm时 ,生长比速率反而下降。与低糖浓度比较 ,较高糖浓度 (2 80g 1 0 0mL)可以使生长迟滞期缩短 ;培养后期菌丝缠绕成浓密颗粒 ,较高糖浓度可以促进生长。在整个培养过程中 ,糖浓度较低时葡萄糖转化成菌体的生长效率明显高于较高葡萄糖浓度的效率。碳源限制生长的连续培养研究结果 ,进一步反映了菌丝不同生长活性使菌丝物具有不同形态结构。菌体量、限制生长底物、菌体生成率的三者关系与细菌有明显的差异。并且 ,在 0 0 1 0～ 0 2 2 0 (h- 1)稀释率范围内菌丝生长符合Contois方程     

丝氨酸蛋白酶抑制剂Serpin1对东亚飞蝗酶学免疫的影响

Serpins是东亚飞蝗Locusta migratoria manilensis体内具有免疫调节功能的一类丝氨酸蛋白酶抑制剂.前期研究发现Serpin1能够降低绿僵菌Metarhizium对蝗虫的杀虫效果,本研究旨在从酶学角度明确Serpin1蛋白抑制绿僵菌毒力的原因,进一步揭示Serpins的功能与作用机制.本实验采用饵剂饲喂的方法进一步明确Serpin1蛋白对绿僵菌侵染东亚飞蝗的抑制效果;测定绿僵菌侵染东亚飞蝗过程中,添加Serpin1蛋白对东亚飞蝗体内保护酶(超氧化物歧化酶SOD、过氧化物酶POD、酚氧化酶PO)、解毒酶(多功能氧化酶MFO、谷胱甘肽转移酶GSTs、乙酰胆碱酯酶AchE)共6种酶的影响,以明确Serpin1对东亚飞蝗酶学免疫的调节作用.结果表明,Serpin1能够显著降低绿僵菌对蝗虫的杀虫效果;将Serpin1与绿僵菌混合后处理东亚飞蝗,12 d后其死亡率为63.5％,显著低于绿僵菌单独处理(死亡率为80.6％).酶活测定结果显示,将绿僵菌IMI330189与Serpin1蛋白混合处理后,与绿僵菌处理组相比,东亚飞蝗体内保护酶SOD和PO的活力总体表现为上调,而POD的活力呈现降低的趋势;解毒酶MFO、GSTs的活性呈现升高趋势,AChE的活力呈现先升高后降低的趋势.上述结果表明,Serpin1蛋白能够增强东亚飞蝗体内解毒酶和保护酶的活性,提高东亚飞蝗的酶学免疫,增强对绿僵菌侵染的抵御能力,从而降低东亚飞蝗的死亡率.本研究为进一步揭示Serpins的功能提供了参考.     

Growth and metabolism of Saccharomyces cerevisiae in chemostat cultures under carbon-, nitrogen-, or carbon- and nitrogen-limiting conditions.

Aerobic chemostat cultures of Saccharomyces cerevisiae were performed under carbon-, nitrogen-, and dual carbon- and nitrogen-limiting conditions. The glucose concentration was kept constant, whereas the ammonium concentration was varied among different experiments and different dilution rates. It was found that both glucose and ammonium were consumed at the maximal possible rate, i.e., the feed rate, over a range of medium C/N ratios and dilution rates. To a small extent, this was due to a changing biomass composition, but much more important was the ability of uncoupling between anabolic biomass formation and catabolic energy substrate consumption. When ammonium started to limit the amount of biomass formed and hence the anabolic flow of glucose, this was totally or at least partly compensated for by an increased catabolic glucose consumption. The primary response when glucose was present in excess of the minimum requirements for biomass production was an increased rate of respiration. The calculated specific oxygen consumption rate, at D = 0.07 h-1, was more than doubled when an additional nitrogen limitation was imposed on the cells compared with that during single glucose limitation. However, the maximum respiratory capacity decreased with decreasing nitrogen concentration. The saturation level of the specific oxygen consumption rate decreased from 5.5 to 6.0 mmol/g/h under single glucose limitation to about 4.0 mmol/g/h at the lowest nitrogen concentration tested. The combined result of this was that the critical dilution rate, i.e., onset of fermentation, was as low as 0.10 h-1 during growth in a medium with a low nitrogen concentration compared with 0.20 h-1 obtained under single glucose limitation.     

Kinetic modeling of <Emphasis Type="Italic">Moorella thermoacetica</Emphasis> growth on single and dual-substrate systems

Acetic acid is an important chemical raw material that can be produced directly from sugars in lignocellulosic biomass. Development of kinetic models that capture the bioconversion dynamics of multiple sugar systems will be critical to optimization and process control in future lignocellulosic biorefinery processes. In this work, a kinetic model was developed for the single- and dual-substrate conversion of xylose and glucose to acetic acid using the acetogen Moorella thermoacetica. Batch fermentations were performed experimentally at 20 g L^?1 total sugar concentration using synthetic glucose, xylose, and a mixture of glucose and xylose at a 1:1 ratio. The product yield, calculated as total product formed divided by total sugars consumed, was 79.2, 69.9, and 69.7 % for conversion of glucose, xylose, and a mixture of glucose and xylose (1:1 ratio), respectively. During dual-substrate fermentation, M. thermoacetica demonstrated diauxic growth where xylose (the preferred substrate) was almost entirely consumed before consumption of glucose began. Kinetic parameters were similar for the single-substrate fermentations, and a strong linear correlation was determined between the maximum specific growth rate μ _max and substrate inhibition constant, K _s . Parameters estimated for the dual-substrate system demonstrated changes in the specific growth rate of both xylose and glucose consumption. In particular, the maximum growth rate related to glucose tripled compared to the single-substrate system. Kinetic growth is affected when multiple substrates are present in a fermentation system, and models should be developed to reflect these features.     

Continuous ethanol production from Jerusalem artichoke tubers. I. Use of free cells of Kluyveromyces marxianus

The Continuous fermentation of Jerusalem artichoke juice to ethanol by free cells of Kluyveromyces marxianus UCD (FST) 55-82 has been studied in a continuous-stirred-tank bioreactor at 35 degrees C and pH 4.6. A maximum yield of 90% of the theoretical was obtained at a dilution rate of 0.05 h(-1). About 95% of the sugars were utilized at dilution rates lower than 0.15 h(-1). Volumetric ethanol productivity and volumetric biomass productivity reached maximum values of 7 g ETOH/L/h and 0.6 g dry wt/L/h, respectively, at a dilution rate of 0.2 h(-1). The maintenance energy coefficient for K. marxianus culture was found to be 0.46 g sugar/g biomass/h/ Oscillatory behavior was following a change in dilution rate from a previous steady state and from batch to continuous culture. Values of specific ethanol production rate and specific sugar uptake were found to increase almost linearly with the increase of the dilution rate. The maximum specific ethanol production rate and maximum specific sugar uptake rate were found to be 2.6 g ethanol/g/ cell/h and 7.9 sugars/g cell/h, respectively. Washout occurred at a dilution rate of 0.41 h(-1).     

Ethanol production from concentrated whey permeate using a fed-batch culture ofKluyveromyces fragilis

Summary Fed-batch fermentation of non-supplemented concentrated whey permeate resulted in high ethanol productivity for feeds of lactose for which batch fermentation had a poor performance. At an initial lactose concentration of 100 g/L and a constant lactose feeding rate of 18 g/h we have obtained: ethanol concentration 64 g/L, ethanol productivity 3.3 g/Lh, lactose consumption 100%, ethanol yield 0.47 g/g, and biomass yield 0.058 g/g.Nomenclature St total lactose fed per medium volume in the bioreactor, g/L - Si initial lactose concentration, g/L - F lactpse feeding rate, g/h - P final ethanol concentration, g/L - Y_p/s ethanol yield, g ethanol/g lactose - Y_x/s biomass yield, g biomass/g lactose - X_S lactose consumption, % - Qp overall ethanol volumetric productivity, g/Lh - m maximum specific growth rate, h - qsm maximum specific lactose consumption rate, g/gh - qpm maximum specific ethanol production rate, g/gh     

Effect of the nitrogen source on caffeine degradation by Aspergillus tamarii

AIMS: To evaluate caffeine degradation and nitrogen requirements during Aspergillus tamarii growth in submerged culture. METHODS AND RESULTS: Aspergillus tamarii spores produced on a coffee infusion agar medium added with sucrose were used. Several caffeine and ammonium sulphate concentrations (0-1 and 0-1.36 g l-1, respectively) were tested simultaneously on fungal biomass production and caffeine degradation. An additional caffeine pulse (4 g l-1) was added for all experiments after 48 h of fermentation. Results revealed that when using 0.90 g l-1 of caffeine and 0.14 g l-1 of ammonium sulphate, biomass production and caffeine degradation were enhanced. Highest biomass production (Xmax = 9.87 g l-1) with a specific growth rate (micro) of 0.073 h-1 and caffeine degradation rate of 0.033 g l-1 h-1, was observed under these conditions. CONCLUSIONS: Caffeine degradation as well as biomass production were characterized. SIGNIFICANCE AND IMPACT OF THE STUDY: These studies set the stage for future characterization studies of intracellular enzymes involved in caffeine degradation. Moreover, results observed may help in the biotreatment of residues from the coffee agroindustry.     

The effect of temperature and pH on ethanol production by free and immobilized cells of Kluyveromyces marxianus grown on Jerusalem artichoke extract

The effect of temperature and pH on the kinetics of ethanol production by free and calcium alginate immobilized cells of Kluyveromyces marxianus grown on Jerusalem artichoke extract was investigated. With the free cells, the ethanol and biomass yields were relatively constant over the temperature range 25-35 degrees C, but dropped sharply beyond 35 degrees C. Other kinetic parameters, specific growth rate, specific ethanol production rate, and specific total sugar uptake rate were maximum at 35 degrees C. However, with the immobilized cells, ethanol yield remained almost constant in the temperature range 25-45 degrees C, and the specific ethanol production rate and specific total sugar uptake rate attained their maximum values at 40 degrees C. For the pH range between 3 and 7, the free-cell optimum for growth and product formation was found to be ca. pH 5. At this pH, the specific growth rate was 0.35 h(-1) and specific ethanol production rate was 2.83 g/g/h. At values higher or lower than pH 5, a sharp decrease in specific ethanol production rate as well as specific growth rate was observed. In comparison, the immobilized cells showed a broad optimum pH profile. The best ethanol production rates were observed between pH 4 and 6.     

Sugar fermentation by <Emphasis Type="Italic">Fusarium oxysporum</Emphasis> to produce ethanol

As a first step in the research on ethanol production from lignocellulose residues, sugar fermentation by Fusarium oxysporum in oxygen-limited conditions is studied in this work. As a substrate, solutions of arabinose, glucose, xylose and glucose/xylose mixtures are employed. The main kinetic and yield parameters of the process are determined according to a time-dependent model. The microorganism growth is characterized by the maximum specific growth rate and biomass productivity, the substrate consumption is studied through the specific consumption rate and biomass yield, and the product formation via the specific production rate and product yields. In conclusion, F. oxysporum can convert glucose and xylose into ethanol with product yields of 0.38 and 0.25, respectively; when using a glucose/xylose mixture as carbon source, the sugars are utilized sequentially and a maximum value of 0.28 g/g ethanol yield is determined from a 50% glucose/50% xylose mixture. Although fermentation performance by F.␣oxysporum is somewhat lower than that of other fermenting microorganisms, its ability for simultaneous lignocellulose-residue saccharification and fermentation is considered as a potential advantage.     

Influence of specific growth rate on biomass yield, productivity, and compostion of Candida utilis in batch and continuous culture.

Candida utilis was grown in batch and continuous culture on prickly pear juice as sole carbon and energy source. In batch culture the maximum specific growth rate (mum) and the substrate yield coefficient (Yps) varied according to sugar concentration. When the fermentation was carried out with 1% sugar, mum and Ys were 0.47/h and 42.6%, respectively. The best yields occurred in a chemostat at the pH range of 3.5 to 4.5 and temperature of 30 C. A beneficial effect on Ys was observed when the dilution rate (D) was increased. At a D of 0.55/h, the productivity was 2.38 g/liter per h. The maintenance coefficient attained a value of 0.09 g of sugar/g of biomass per h. Increases of D produced higher protein contents of the biomass. The information obtained indicates that protein production with Candida utilis, using prickly pear juice, should be carried out a high dilution rates where the Ys and protein content of the cell mass are also higher.     

Influence of specific growth rate on biomass yield, productivity, and compostion of Candida utilis in batch and continuous culture.

Candida utilis was grown in batch and continuous culture on prickly pear juice as sole carbon and energy source. In batch culture the maximum specific growth rate (mum) and the substrate yield coefficient (Yps) varied according to sugar concentration. When the fermentation was carried out with 1% sugar, mum and Ys were 0.47/h and 42.6%, respectively. The best yields occurred in a chemostat at the pH range of 3.5 to 4.5 and temperature of 30 C. A beneficial effect on Ys was observed when the dilution rate (D) was increased. At a D of 0.55/h, the productivity was 2.38 g/liter per h. The maintenance coefficient attained a value of 0.09 g of sugar/g of biomass per h. Increases of D produced higher protein contents of the biomass. The information obtained indicates that protein production with Candida utilis, using prickly pear juice, should be carried out a high dilution rates where the Ys and protein content of the cell mass are also higher.