不同补料发酵方式对发夫酵母产虾青素的影响

对发夫酵母的不同补料发酵方式进行了研究,期望提高发酵产率,以便对工业化生产提供一定的指导作用。实验结果表明：采用恒pH葡萄糖-氨水流加培养,色素量和生物量均具有最大值,分别为54.3μg/ml和49.5μg/ml;其次是指数流加培养,色素量和生物量分别为49.9μg/ml和47.4mg/ml;恒pO2流加方式下色素量和生物量分别为34.04ug/ml和35.4mg/ml;恒pH葡萄糖流加方式所得的色素量和生物量最小,分别为32.3μg/ml和31.5mg/ml。不同的补料发酵方式对发夫酵母生长和色素形成的影响很大。     

补料工艺对两株法夫酵母菌株产虾青素的影响

【目的】考察不同补料工艺对法夫酵母菌株生长和虾青素合成的影响。【方法】对法夫酵母JMU-VDL668和JMU-MVP14菌株在7 L罐中进行分批及分批补料培养; 同时, 测定发酵过程中生物量、虾青素和葡萄糖含量的变化。【结果】采用恒DO补料, 法夫酵母JMU-VDL668菌株获得的生物量最大(64.6 g/L), 是分批培养的2.2倍; 采用恒pH补料发酵, 虾青素的产量最高(20.6 mg/L), 是分批培养的1.5倍。与JMU-VDL668菌株不同, 虾青素高产菌株JMU-MVP14菌株采用恒pH补料, 获得生物量最大(48.5 g/L), 但虾青素产量大大降低(仅17.5 mg/L); 采用脉冲补料, 虾青素产量最高, 达到414.1 mg/L, 与分批发酵相比提高了200.2%; 采用恒DO补料, 生物量(38.5 g/L)和虾青素产量(403.2?mg/L)增加显著, 与分批发酵相比分别提高了133.1%和192.3%。【结论】不同补料工艺对法夫酵母菌株生产虾青素影响很大。其中, 采用恒pH补料工艺, 法夫酵母JMU-VDL668菌株可以获得最高的虾青素产量, 而采用脉冲补料工艺, 最适于法夫酵母JMU-MVP14菌株发酵生产虾青素。     

一株法夫酵母虾青素高产菌株的生产性能

为了评价虾青素高产菌株-法夫酵母JMU-MVP14的生产性能及建立虾青素高产发酵技术,通过测定糖、生物量、虾青素产量、总类胡萝卜素产量等发酵参数,用摇瓶试验对比了法夫酵母JMU-MVP14和出发菌株的差异,用7 L罐试验对比了pH值调控方式及补料培养基成分对发酵的影响,用1 m3罐试验评估了法夫酵母JMU-MVP14高密度发酵虾青素的产量水平。摇瓶发酵结果表明,法夫酵母JMU-MVP14虾青素及总类胡萝卜素的细胞产率分别达到6.01 mg/g及10.38 mg/g;7 L罐分批发酵试验结果表明,自动流加调     

法夫酵母PLX-ll发酵纤维素酶水解物合成虾青素

法夫酵母（Phaffiarhodozyma)PLX朅ll菌株能够发酵纤维素酶水解物进行虾青素的生物合成。纤维素的酶解物主要为纤维二糖和葡萄糖,在另外添加适量其它营养物后可被法夫酵母发酵用于生长及合成虾青素。摇瓶试验结果表明,培养108h,法夫酵母的生物量可达2.3g／L,虾青素的产率达913.4g／g干细胞,虾青素体积产率为2.1mg／L。在2L罐的发酵试验中,法夫酵母的生物量可达3.23g／L（第96h）,虾青素的产率达581.4g／g干细胞,虾青素体积产率达1.88mg／L。     

法夫酵母PLX-All发酵纤维素酶水解物合成虾青素

法夫酵母（Phaffia rhodozyma)PLX-All菌株能够发酵纤维素酶水解物进行虾青素的生物合成。纤维素的酶解物主要为纤维二糖和葡萄糖,在另外添加适量其它营养物后可被法夫酵母发酵用于生长及合成虾青素。摇瓶试验结果表明,培养108h,法夫酵母的生物量可达2.3g／L,虾青素的产率达913.4g／g干细胞,虾青素体积产率为2.1mg／L。在2L罐的发酵试验中,法夫酵母的生物量可达3.23g／L（第96h）,虾青素的产率达581.4g／g干细胞,虾青素体积产率达1.88mg／L。     

法夫酵母PLX-All发酵纤维素酶水解物合成虾青素*

法夫酵母（Phaffia rhodozyma)PLX-All菌株能够发酵纤维素酶水解物进行虾青素的生物合成。纤维素的酶解物主要为纤维二糖和葡萄糖,在另外添加适量其它营养物后可被法夫酵母发酵用于生长及合成虾青素。摇瓶试验结果表明,培养108h,法夫酵母的生物量可达2.3g／L,虾青素的产率达913.4g／g干细胞,虾青素体积产率为2.1mg／L。在2L罐的发酵试验中,法夫酵母的生物量可达3.23g／L（第96h）,虾青素的产率达581.4g／g干细胞,虾青素体积产率达1.88mg／L。     

利用亚硝酸钠选育法夫酵母虾青素高产菌株

以亚硝酸钠作为筛选剂选择性分离法夫酵母虾青素高产菌株。实验研究表明,在亚硝酸钠存在的情况下,法夫酵母的生长和虾青素合成量均会减少;当亚硝酸钠浓度为5000μmol/L时,法夫酵母的致死率为100%。挑取200株经过甲基磺酸乙酯（EMS）诱变后的法夫酵母,以5000μmol/L的亚硝酸钠为筛选剂摇瓶发酵后测得虾青素体积产率为正突变的菌株有87株,正突变率为43.5%。挑取其中8株进行复筛,编号为N030的菌株比出发菌株的虾青素体积产率和细胞产率分别提高了39.3%和89.3%。结果说明,亚硝酸钠可作为法夫酵母虾青素高产菌株的筛选剂,用于提高菌种的筛选效率。     

氧载体强化氧传递促进法夫酵母虾青素的合成*

法夫酵母生物合成虾青素是强好氧发酵过程,溶氧水平直接影响细胞虾青素的产率。本文对虾青素的氧载体强化氧传递双液相发酵进行了研究。实验结果表明,添加豆油(作为氧载体)可提高法夫酵母发酵时的溶氧水平,促进虾青素的合成:添加豆油 0.5-5.0%(w/v),虾青素产量随豆油添加量逐步提高,最高时达到2.98mg/L,对照组虾青素产率为2.50mg/L。并证明产量的提高是单位质量细胞的虾青素合成效率提高的结果。摇瓶培养时转速的高低不同,对豆油的最适添加量存在影响。较高摇瓶转速有利于豆油在培养基中分散,从而利于强化氧的传递。     

氧载体强化氧传递促进法夫酵母虾青素的合成

法夫酵母生物合成虾青素是强好氧发酵过程,溶氧水平直接影响细胞虾青素的产率。本文对虾青素的氧载体强化氧传递双液相发酵进行了研究。实验结果表明,添加豆油(作为氧载体)可提高法夫酵母发酵时的溶氧水平,促进虾青素的合成：添加豆油 0.5-5.0％ (w／v),虾青素产量随豆油添加量逐步提高,最高时达到 2.98mg/L,对照组虾青素产率为 2.50mg/L。并证明产量的提高是单位质量细胞的虾青素合成效率提高的结果。摇瓶培养时转速的高低不同,对豆油的最适添加量存在影响。较高摇瓶转速有利于豆油在培养基中分散,从而利于强化氧的传递。     

法夫酵母PLX—A11发酵纤维素酶水解物合成虾青素

法夫酵母（Ｐｈａｆｆｉａ ｒｈｏｄｏｚｙｍａ）ＰＬＸ－Ａ１１菌株能够发酵纤维素酶水解物进行虾青素的生物合成。纤维素的酶解物主要为纤维二糖和葡萄糖,在另外添加适量其它营养物后可被法夫酵母发酵用于生长及俣成虾青素。摇瓶试验结果表明,培养１０８ｈ,法夫酵母的生物量可达２．３ｇ／Ｌ,虾青素的产率达９１３．４μｇ／ｇ干细胞,虾青素体积产率为２．１ｍｇ／Ｌ。在２Ｌ罐的发酵试验中,法夫酵母的生物量可达３．２３ｇ     

Modeling of Xanthophyllomyces dendrorhous growth on glucose and overflow metabolism in batch and fed-batch cultures for astaxanthin production

An astaxanthin-producing yeast Xanthophyllomyces dendrorhous ENM5 was cultivated in a liquid medium containing 50 g/L glucose as the major carbon source in stirred fermentors (1.5-L working volume) in fully aerobic conditions. Ethanol was produced during the exponential growth phase as a result of overflow metabolism or fermentative catabolism of glucose by yeast cells. After accumulating to a peak of 3.5 g/L, the ethanol was consumed by yeast cells as a carbon source when glucose in the culture was nearly exhausted. High initial glucose concentrations and ethanol accumulation in the culture had inhibitory effects on cell growth. Astaxanthin production was partially associated with cell growth. Based on these culture characteristics, we constructed a modified Monod kinetic model incorporating substrate (glucose) and product (ethanol) inhibition to describe the relationship of cell growth rate with glucose and ethanol concentrations. This kinetic model, coupled with the Luedeking-Piret equation for the astaxanthin production, gave satisfactory prediction of the biomass production, glucose consumption, ethanol formation and consumption, and astaxanthin production in batch cultures over 25-75 g/L glucose concentration ranges. The model was also applied to fed-batch cultures to predict the optimum feeding scheme (feeding glucose and corn steep liquor) for astaxanthin production, leading to a high volumetric yield (28.6 mg/L) and a high productivity (5.36 mg/L/day).     

Perfusion culture process plus H2O2 stimulation for efficient astaxanthin production by Xanthophyllomyces dendrorhous

A semicontinuous perfusion culture process (repeated medium renewal with cell retention) was evaluated together with batch and repeated fed-batch processes for astaxanthin production in shake-flask cultures of Xanthophyllomyces dendrorhous. The perfusion process with 25% medium renewal every 12 h for 10 days achieved a biomass density of 65.6 g/L, a volumetric astaxanthin yield of 52.5 mg/L, and an astaxanthin productivity of 4.38 mg/L-d, which were 8.4-fold, 5.6-fold, and 2.3-fold of those in the batch process, 7.8 g/L, 9.4 mg/L, and 1.88 mg/L-d, respectively. The incorporation of hydrogen peroxide (H(2)O(2)) stimulation of astaxanthin biosynthesis into the perfusion process further increased the astaxanthin yield to 58.3 mg/L and the productivity to 4.86 mg/L-d. The repeated fed-batch process with 8 g/L glucose and 4 g/L corn steep liquor fed every 12 h achieved 42.2 g/L biomass density, 36.5 mg/L astaxanthin yield, and 3.04 mg/L-d astaxanthin productivity. The lower biomass and astaxanthin productivity in the repeated fed-batch than in the perfusion process may be mostly attributed to the accumulation of inhibitory metabolites such as ethanol and acetic acid in the culture. The study shows that perfusion process plus H(2)O(2) stimulation is an effective strategy for enhanced astaxanthin production in X. dendrorhous cultures.     

Production of β-carotene by recombinant Escherichia coli with engineered whole mevalonate pathway in batch and fed-batch cultures

Recombinant Escherichia coli engineered to contain the whole mevalonate pathway and foreign genes for β-carotene biosynthesis, was utilized for production of β-carotene in bioreactor cultures. Optimum culture conditions were established in batch and pH-stat fed-batch cultures to determine the optimal feeding strategy thereby improving production yield. The specific growth rate and volumetric productivity in batch cultures at 37°C were 1.7-fold and 2-fold higher, respectively, than those at 28°C. Glycerol was superior to glucose as a carbon source. Maximum β-carotene production (titer of 663 mg/L and overall volumetric productivity of 24.6 mg/L × h) resulted from the simultaneous addition of 500 g/L glycerol and 50 g/L yeast extract in pH-stat fed-batch culture.     

Astaxanthin from Jerusalem artichoke: Production by fed-batch fermentation using Phaffia rhodozyma and application in cosmetics

Jerusalem artichoke extract or powder was used for astaxanthin production using Phaffia rhodozyma without acidic or enzymatic inulin hydrolysis. The culture medium containing Jerusalem artichoke as carbon source was optimized, and feeding strategies, including constant, exponential, pH-stat, and substrate feedback fed-batch fermentations, were also compared for enhancing the cell biomass and astaxanthin synthesis by P. rhodozyma. Substrate-feedback fed-batch fermentation resulted in the highest dry cell weight of 83.60 g/L, with a carotenoid concentration and yield of 982.50 mg/L and 13.30 mg/g, respectively, under optimized medium components using Jerusalem artichoke extract as carbon source in a 3-L stirred-tank bioreactor. Moreover, 482.50 mg/L of carotenoids and 253.10 mg/L of astaxanthin were obtained by continuous feeding of Jerusalem artichoke powder, which was used as carbon source. Astaxanthin essence with high DPPH-scavenging activity was obtained from the extracted astaxanthin, and the DPPH free radical scavenging rate of 40 ppm astaxanthin essence reached 76.29%. When stored at 4 °C, astaxanthin essence showed the highest stability, with a minimum k value of 0.0099 week⁻¹ and maximum half-life (t_1/2) value of 70 weeks.     

Astaxanthin production by Phaffia rhodozymaenhanced in fed-batch culture with glucose and ethanol feeding

Of various carbon sources, examined for the cultivation of Phaffia rhodozyma, ethanol enhanced the astaxanthin content but severely decreased growth. Therefore, high cell mass was obtained by glucose fed-batch culture with pH-stat, and the ethanol feeding was performed based on DO-stat. As a result of this two-stage fed-batch cultivation, 30 g dry cells per liter were obtained, and the astaxanthin content reached 0.72 mg/g, which was 2.2-fold higher than that without ethanol feeding.     

High cell density cultivation of Escherichia coli at controlled specific growth rate.

A high cell density cultivation (HCDC) for growth of Escherichia coli in an especially designed glucose/mineral salt medium is proposed. The HCDC essentially starts as a batch process which is followed by a two-phase fed-batch cultivation. After unlimited growth at mu max = 0.45 h-1 in the batch part, growth was controlled at a reduced specific growth rate (mu = 0.11 h-1 less than mu max) over a period of 3 doubling times in which the biomass concentration increased from 12 to 95 g 1(-1) (phase 1 of fed-batch cultivation). Control of growth (mu) was realized by a PO2 control loop (by variation of glucose feeding) and a mu control loop (by variation of agitation speed N) while the actual mu was calculated from the off-gas composition. If the agitation rate cannot be increased anymore the mu controller is switched off (end of phase 1). In the following phase 2, mu declines, however, the still acting pO2 (glucose) controller guarantees sufficient O2 supply till the end of the cultivation with a biomass concentration of 110 g 1(-1) (dry mass). The proposed HCDC suppresses generation of inhibitory by-products and the high yield coefficients indicate the economy of the process.     

Effects of carbon sources and feeding strategies on heparosan production by Escherichia coli K5

This work aimed to develop an optimal carbon source feeding strategy to achieve maximal production of heparosan as a precursor of bioengineered heparin by Escherichia coli K5. Glycerol gave higher heparosan titer and productivity compared to glucose. The maximum heparosan production (187 mg/L) and heparosan productivity (5.19 mg/L/h) in glycerol-defined medium were 26.4% higher than the heparosan production (148 mg/L) and heparosan productivity (4.11 mg/L/h) in glucose-defined medium. DO-stat feeding approach as compared to pH-stat feeding, exponential feeding, exponential combined with pH-stat feeding, and constant rate feeding gave the highest heparosan titer at 8.63 g/L, which was nine times that of batch culture. The obtained optimal glycerol feeding strategy may be useful for the scaling-up of microbial heparosan production.