Biocatalytic resolution of benzyl glycidyl ether and its derivates by Talaromyces flavus: effect of phenyl ring substituents on enantioselectivity

Talaromyces flavus containing a constitutive epoxide hydrolase (EH) resolved racemic benzyl glycidyl ether and nine derivatives into their (R)-enantiomers. After optimization of the fermentation conditions, the specific EH activity and biomass concentration were improved from 13.5 U/g DCW and 14.8 g DCW/l to 26.2 U/g DCW and 31.3 g DCW/l, respectively, with final values for e.e. ( s ) of 96 % and E of 13 with (R)-benzyl glycidyl ether. Substituents on the phenyl ring, however, gave low enantioselectivities.     

Optimization of polyhydroxybutyrate production from a wild type and two mutant strains of Rhodobacter sphaeroides using statistical method

Interaction studies using central composite design (CCD) gave the optimum concentrations of acetate at 4 g l(-1) and (NH4)2SO4 at 0.01 g l(-1) with an optimum temperature of 35 degrees C. Rhodobacter sphaeroides N20 gave the highest PHB (7.8 g l(-1)) and biomass (DCW) (8.2 g l(-1)) values compared to the wild type strain and the mutant strain U7. The CCD results predicted that the optimum medium for the mutant strain N20 consisted of 3.90 g l(-1) acetate, 0.01 g l(-1) (NH4)2SO4 at 33.5 degrees C (R2=0.985). Validation of this model by culturing the mutant strain in this optimum medium exhibited similar values of PHB (7.76 g l(-1)), biomass (8.32 g l(-1)) and the PHB content in the cell 93.2% of DCW. Similar amounts of PHB were also obtained in batch fermentations using a 5-l bioreactor. The effect of pH and aeration rate was also studied and the optimum values were found to be pH 7.0 with an aeration rate of 1.0 vvm. Under these optimal conditions, strain N20 produced the highest amount of PHB production (8.76 g l(-1)), PHB content (95.4% of DCW) as well as the product yield (Yp/x) (0.72). These results are the highest values ever obtained from photosynthetic bacteria reported so far.     

Measurement and analysis of intracellular ATP levels in metabolically engineered Zymomonas mobilis fermenting glucose and xylose mixtures

Intracellular adenosine-5'-triphosphate (ATP) levels were measured in a metabolically engineered Zymomonas mobilis over the course of batch fermentations of glucose and xylose mixtures. Fermentations were conducted over a range of pH (5-6) in the presence of varying initial amounts of acetic acid (0-8 g/L) using a 10% (w/v) total sugar concentration (glucose only, xylose only, or 5% glucose/5% xylose mixture). Over the design space investigated, ethanol process yields varied between 56.6% and 92.3% +/- 1.3% of theoretical, depending upon the test conditions. The large variation in process yields reflects the strong effect pH plays in modulating the inhibitory effect of acetic acid on fermentation performance. A corresponding effect was observed on maximum cellular specific growth rates, with the rates varying between a low of 0.15 h(-1) observed at pH 5 in the presence of 8 g/L acetic acid to a high of 0.32 +/- 0.02 h(-1) obtained at pH 5 or 6 when no acetic acid was initially present. While substantial differences were observed in intracellular specific ATP concentration profiles depending upon fermentation conditions, maximum intracellular ATP accumulation levels varied within a relatively narrow range (1.5-3.8 mg ATP/g dry cell mass). Xylose fermentations produced and accumulated ATP at much slower rates than mixed sugar fermentations (5% glucose, 5% xylose), and the ATP production and accumulation rates in the mixed sugar fermentations were slightly slower than in glucose fermentations. Results demonstrate that higher levels of acetic acid delay the onset and influence the extent of intracellular ATP accumulation. ATP production and accumulation rates were most sensitive to acetic acid at lower values of pH.     

Isolation and partial characterization of alkaline feruloyl esterases from Aspergillus niger CFR 1105 grown on wheat bran

Feruloyl esterases (FAEs) of a strain of Aspergillus niger (CFR 1105) grown in solid state (ssf) and submerged fermentations (smf) using wheat bran both as carbon source and inducer of the enzyme were studied. The feruloyl esterase activity was maximum after 4 days in solid state as well as in submerged fermentations (32.5 and 31.5 U/g dry weight of wheat bran respectively) and the enzyme titers were comparable. The specific activity was maximum on day 2 in ssf (12.8 U/mg protein) and it decreased thereafter, whereas specific activity was maximum on day 3 (11.7 U/mg protein) in smf and it remained constant up to 5 days. Two isoenzymes of feruloyl esterases were isolated and purified to homogeneity by conventional protein purification methods from the day 5 culture filtrate of A. niger grown in smf. On a DEAE-cellulose column, two enzyme activity peaks designated as FAE-1 and FAE-2 were eluted with 0.3 and 0.35 M NaCl, respectively. They were monomeric glycoproteins with approximate molecular weights of 50 kDa (FAE-1) and 55 kDa (FAE-2), respectively. FAE-1 showed a temperature optimum of 40°C whereas FAE-2 showed a wider temperature optimum of 40–50°C. FAE-1 and FAE-2 exhibited pH optima of 9 and 6, respectively, and both were stable over a pH range of 6–9. The ability of the enzyme to be active in alkaline pH may be advantageous in biotechnological applications.     

恒细胞密度发酵策略提高重组毕赤酵母生产碱性果胶酶的表达效率

为了提高重组毕赤酵母生产碱性果胶酶(Alkaline polygalacturonate lyase,PGL)的比速率,开发了一种新的恒细胞密度发酵策略。通过不同的甲醇流加方式,实现发酵过程细胞密度的合理控制。实验结果表明:控制细胞密度为75 g/L的策略为最优,最终单位发酵液体积生产强度和单位菌体生产强度为6.11 U/(mL.h)和81.5 U/(g.h),分别比传统高密度发酵提高了42.1%和191.2%,最终PGL酶活为441.9 U/mL。此外,该策略还具有提高细胞活性和降低蛋白酶降解作用等优势。     

重组点状产气单胞菌脯氨酰内肽酶的纯化和鉴定

报道重组点状产气单胞菌脯氨酰内肽酶(简称apPEP)的基因工程下游工艺研究。工程菌株E.coli BL21/pKKH\|PEP表达产物apPEP为可溶性蛋白,在NBS BioFlo 3000型5L自控发酵罐中经14h培养每升发酵液可达到22.5g干重菌体,含apPEP 3.0g左右。发酵菌体经超声破碎、硫酸铵沉淀后,依次经Sephadex G-25、High performance Q sepharose FF(HP\|Q)、Phenyl separose 6 FF柱层析分离纯化,每升发酵产物最终可得0.86g纯度达96%的重组apPEP,比活力达到65.5u/mg,整个纯化工艺的蛋白回收率为8.2%,活力回收率为24.4%。纯化的apPEP经电喷雾质谱测定分子量为76464±30D,N端氨基酸序列与基因序列推导的一致。等电点为pI6.0左右。与Aeromonas hydrophila来源的PEP(pI=5.5)相近。     

Large‐scale synthesis of tert‐butyl (3R,5S)‐6‐chloro‐3,5‐dihydroxyhexanoate by a stereoselective carbonyl reductase with high substrate concentration and product yield

To biosynthesize the (3R,5S)‐CDHH in an industrial scale, a newly synthesized stereoselective short chain carbonyl reductase (SCR) was successfully cloned and expressed in Escherichia coli. The fermentation of recombinant E. coli harboring SCR was carried out in 500 L and 5000 L fermenters, with biomass and specific activity of 9.7 g DCW/L, 15749.95 U/g DCW, and 10.97 g DCW/L, 19210.12 U/g DCW, respectively. The recombinant SCR was successfully applied for efficient production of (3R,5S)‐CDHH. The scale‐up synthesis of (3R,5S)‐CDHH was performed in 5000 L bioreactor with 400 g/L of (S)‐CHOH at 30°C, resulting in a space‐time yield of 13.7 mM/h/g DCW, which was the highest ever reported. After isolation and purification, the yield and d.e. of (3R,5S)‐CDHH reached 97.5% and 99.5%, respectively. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 33:612–620, 2017     

Multi-copy expression and fed-batch production of Rhodotorula araucariae epoxide hydrolase in Yarrowia lipolytica

Epoxide hydrolases (EHs) of fungal origin have the ability to catalyze the enantioselective hydrolysis of epoxides to their corresponding diols. However, wild type fungal EHs are limited in substrate range and enantioselectivity. Additionally, the production of fungal epoxide hydrolase (EH) by wild-type strains is typically very low. In the present study, the EH-encoding gene from Rhodotorula araucariae was functionally expressed in Yarrowia lipolytica, under the control of a growth phase inducible hp4d promoter, in a multi-copy expression cassette. The transformation experiments yielded a positive transformant, with a final EH activity of 220 U/g dw in shake-flask cultures. Evaluation of this transformant in batch fermentations resulted in ~ 7-fold improvement in EH activity over the flask scale. Different constant specific feed rates were tested in fed-batch fermentations, resulting in an EH activity of 1,750 U/g dw at a specific feed rate of ~ 0.1 g/g/h, in comparison to enzyme production levels of 0.3 U/g dw for the wild type R. araucariae and 52 U/g dw for an Escherichia coli recombinant strain expressing the same gene. The expression of EH in Y. lipolytica using a multi-copy cassette demonstrates potential for commercial application.     

碱性果胶酶在重组毕赤酵母中高效表达的关键因素研究

为提高重组毕赤酵母生产碱性果胶酶的产量和生产强度, 在摇瓶条件下优化了重组毕赤酵母生产碱性果胶酶的关键因素。结果表明, 以下条件：初始甘油浓度40 g/L、初始甲醇浓度3.1 g甲醇/g DCW、每24 h添加0.51 g甲醇/g DCW、诱导表达周期72 h、250 mL三角瓶诱导培养基装液量30 mL、初始pH 6.0, 最适于菌体生长与产物表达。在此基础上, 7 L罐上通过恒速流加甘油进一步提高细胞密度, 诱导阶段甲醇采取前期恒速流加和后期DO-stat, 发酵结束菌体干重达80 g/L, 酶活为217 U/mL, 比摇瓶结果提高了66.2%。     

碱性果胶酶在重组毕赤酵母中高效表达的关键因素研究

为提高重组毕赤酵母生产碱性果胶酶的产量和生产强度,在摇瓶条件下优化了重组毕赤酵母生产碱性果胶酶的关键因素。结果表明,以下条件：初始甘油浓度40g／L、初始甲醇浓度3.1g甲醇／gDCW、每24h添加0.51g甲醇／gDCW、诱导表达周期72h、250mL三角瓶诱导培养基装液量30mL、初始pH6,0,最适于菌体生长与产物表达。在此基础上,7L罐上通过恒速流加甘油进一步提高细胞密度,诱导阶段甲醇采取前期恒速流加和后期DO-stat,发酵结束菌体干重达80g／L,酶活为217U／mL,比摇瓶结果提高了66.2％。     

(R)-phenylacetylcarbinol production in aqueous/organic two-phase systems using partially purified pyruvate decarboxylase from Candida utilis

Aqueous/organic two-phase systems have been evaluated for enhanced production of (R)-phenylacetylcarbinol (PAC) from pyruvate and benzaldehyde using partially purified pyruvate decarboxylase (PDC) from Candida utilis. In a solvent screen, octanol was identified as the most suitable solvent for PAC production in the two-phase system in comparison to butanol, pentanol, nonanol, hexane, heptane, octane, nonane, dodecane, methylcyclohexane, methyl tert butyl ether, and toluene. The high partitioning coefficient of the toxic substrate benzaldehyde in octanol allowed delivery of large amounts of benzaldehyde into the aqueous phase at a concentration less than 50 mM. PDC catalyzed the biotransformation of benzaldehyde and pyruvate to PAC in the aqueous phase, and continuous extraction of PAC and byproducts acetoin and acetaldehyde into the octanol phase further minimized enzyme inactivation, and inhibition due to acetaldehyde. For the rapidly stirred two-phase system with a 1:1 phase ratio and 8.5 U/mL carboligase activity, 937 mM (141 g/L) PAC was produced in the octanol phase in 49 h with an additional 127 mM (19 g/L) in the aqueous phase. Similar concentrations of PAC could be produced in the slowly stirred phase separated system at this enzyme level, although at a much slower rate. However at lower enzyme concentration very high specific PAC production (128 mg PAC/U carboligase at 0.9 U/mL) was achieved in the phase separated system, while still reaching final PAC levels of 102 g/L in octanol and 13 g/L in the aqueous phase. By comparison with previously published data by our group for a benzaldehyde emulsion system without octanol (50 g/L PAC, 6 mg PAC/U carboligase), significantly higher PAC concentrations and specific PAC production can be achieved in an octanol/aqueous two-phase system.     

Effect of various process parameters on morphology, rheology, and polygalacturonase production by Aspergillus sojae in a batch bioreactor

The effects of pH, agitation speed, and dissolved oxygen tension (DOT), significant in common fungal fermentations, on the production of polygalacturonase (PG) enzyme and their relation to morphology and broth rheology were investigated using Aspergillus sojae in a batch bioreactor. All three factors were effective on the response parameters under study. An uncontrolled pH increased biomass and PG activity by 27% and 38%, respectively, compared to controlled pH (pH 6) with an average pellet size of 1.69 +/- 0.48 mm. pH did not significantly affect the broth rheology but created an impact on the pellet morphology. Similarly, at constant agitation speed the maximum biomass obtained at 500 rpm and at 30 h was 3.27 and 3.67 times more than at 200 and 350 rpm, respectively, with an average pellet size of 1.08 +/- 0.42 mm. The maximum enzyme productivity of 0.149 U mL-1 h-1 was obtained at 200 rpm with an average pellet size of 0.71 +/- 0.35 mm. Non-Newtonian and pseudoplastic broth rheology was observed at 500 rpm agitation speed, broth rheology exhibited dilatant behavior at the lower agitation rate (200 rpm), and at the medium agitation speed (350 rpm) the broth was close to Newtonian. Furthermore, a DOT range of 30-50% was essential for maximum biomass formation, whereas only 10% DOT was required for maximum PG synthesis. Non-Newtonian shear thickening behavior (n > 1.0) was depicted at DOT levels of 10% and 30%, whereas non-Newtonian shear thinning behavior (n < 1.0) was dominant at 50% DOT. The overall fermentation duration (50-70 h) was considerably shorter compared to common fungal fermentations, revealing the economic feasibility of this particular process. As a result this study not only introduced a new strain with a potential of producing a highly commercially significant enzyme but also provided certain parameters significant in the design and mathematical modeling of fungal bioprocesses.     

Control of Lactobacillus contaminants in continuous fuel ethanol fermentations by constant or pulsed addition of penicillin G

The addition of penicillin G to combat microbial contamination in continuous fuel alcohol fermentations was performed using both continuous and pulsed addition regimes. In continuous fermentations where both Saccharomyces cerevisiae and Lactobacillus paracasei were present, the mode of addition of penicillin G determined final numbers of viable L. paracasei. When the same overall average concentration of penicillin G was added in both pulsed and continuous modes, the initial viable number of L. paracasei (8.0 x 10(9) cfu ml(-1)) decreased to a greater degree (1.02 x 10(5) cfu ml(-1) L. paracasei) when penicillin G was pulsed at 6 h frequencies at an overall average concentration of 2,475 U/l than when penicillin G was added continuously at 2,475 U/l (2.77 x 10(5) cfu ml(-1) L. paracasei). Pulsed additions over longer frequencies at 2,475 U/l were not as effective in reducing viable bacteria. Viable yeasts increased during both treatment conditions by more than 2-fold. The two addition regimes also eliminated the 40% decrease in ethanol concentration caused by the intentional bacterial infection. Although there was 3 times more bacterial death with 6 h pulsed additions compared to continuous additions of penicillin G at 2,475 U/l, there was, by that point, no practical difference in either final ethanol concentration or relative ethanol recovery.     

Enzymatic (R)-phenylacetylcarbinol production in benzaldehyde emulsions

(R)-Phenylacetylcarbinol [(R)-PAC)] is the chiral precursor for the production of the pharmaceuticals ephedrine and pseudoephedrine. Reaction conditions were improved to achieve increased (R)-PAC levels in a simple batch biotransformation of benzaldehyde emulsions and pyruvate, using partially purified pyruvate decarboxylase (PDC) from the filamentous fungus Rhizopus javanicus NRRL 13161 as the catalyst. Lowering the temperature from 23 degrees C to 6 degrees C decreased initial rates but increased final (R)-PAC concentrations. Addition of ethanol, which increases benzaldehyde solubility, was not beneficial for (R)-PAC production. It was established that proton uptake during biotransformation increases the pH above 7 thereby limiting (R)-PAC production. For small-scale studies, biotransformations were buffered with 2-2.5 M MOPS (initial pH 6.5). High concentrations of MOPS as well as some alcohols and KCl stabilised PDC. A balance between PDC and substrate concentrations was determined with regards to ( R)-PAC production and yields on enzyme and substrates. R. javanicus PDC (7.4 U/ml) produced 50.6 g/l (337 mM) ( R)-PAC in 29 h at 6 degrees C with initial 400 mM benzaldehyde and 600 mM pyruvate. Molar yields on consumed benzaldehyde and pyruvate were 97% and 59%, respectively, with 17% pyruvate degraded and 24% converted into acetaldehyde and acetoin; 43% PDC activity remained, indicating reasonable enzyme stability at high substrate and product concentrations.     

Glucoamylase production by solid-state fermentation using rice flake manufacturing waste products as substrate

Glucoamylase production has been investigated by solid-state fermentation of agro-industrial wastes generated during the processing of paddy to rice flakes (categorized as coarse, medium and fine waste), along with wheat bran and rice powder by a local soil isolate Aspergillus sp. HA-2. Highest enzyme production was obtained with wheat bran (264 +/- 0.64 U/gds) followed by coarse waste (211.5 +/- 1.44 U/gds) and medium waste (192.1 +/- 1.15 U/gds) using 10(6) spores/ml as inoculum at 28 +/- 2 degrees C, pH 5. A combination of wheat bran and coarse waste (1:1) gave enzyme yield as compared to wheat bran alone. Media supplementation with carbon source (0.04 g/gds) as sucrose in wheat bran and glucose in coarse and medium waste increased enzyme production to 271.2 +/- 0.92, 220.2 +/- 0.75 and 208.2 +/- 1.99 U/gds respectively. Organic nitrogen supplementation (yeast extract and peptone, 0.02 g/gds) showed a higher enzyme production compared to inorganic source. Optimum enzyme activity was observed at 55 degrees C, pH 5. Enzyme activity was enhanced in the presence of calcium whereas presence of EDTA gave reverse effect.     

Use of fed-batch cultivation for achieving high cell densities for the pilot-scale production of a recombinant protein (phenylalanine dehydrogenase) in Escherichia coli

A fed-batch process for the high cell density cultivation of E. coli TG1 and the production of the recombinant protein phenylalanine dehydrogenase (PheDH) was developed. A model based on Monod kinetics with overflow metabolism and incorporating acetate utilization kinetics was used to generate simulations that describe cell growth, acetate production and reconsumption, and glucose consumption during fed-batch cultivation. Using these simulations a predetermined feeding profile was elaborated that would maintain carbon-limited growth at a growth rate below the critical growth rate for acetate formation (mu < mu(crit)). Two starvation periods are incorporated into the feed profile in order to induce acetate utilization. Cell concentrations of 53 g dry cell weight (DCW)/L were obtained with a final intracellular product concentration of recombinant protein corresponding to approximately 38% of the total cell protein. The yield of PheDH was 129 U/mL with a specific activity of 1.2 U/mg DCW and a maximum product formation rate of 0.41 U/mg DCW x h. The concentration of aectate was maintained below growth inhibitory levels until 3 h before the end of the fermentation when the concentration reached a maximum of 10.7 g/L due to IPTG induction of the recombinant protein.     

Comparative studies on enzyme preparations and role of cell components for (R)-phenylacetylcarbinol production in a two-phase biotransformation

Whole cell pyruvate decarboxylase (PDC) from Candida utilis enhanced the enzymatic production of (R)-phenylacetylcarbinol (PAC) in an aqueous/octanol biotransformation compared to the partially purified PDC especially for a lower range of initial activities (0.3-2.5 U/mL). With an initial activity of 1.1 U/mL and at a 1:1 phase volume ratio, whole cell PDC achieved a maximum specific PAC production of 42 mg/U (2.8 g/L/h) in comparison to 13 mg/U (0.9 g/L/h) for partially purified PDC. The enhanced performance of whole cell PDC was associated with high stability towards the substrate benzaldehyde. The strong PDC inactivation by benzaldehyde was minimal even when whole cells were broken as long as cell debris was not removed from the broken cells. Biotransformations with various cellular components added to partially purified PDC revealed that membrane components especially 2 mg/mL phosphatidylcholine enhanced PAC concentrations. The role of surfactants was further confirmed from the results with synthetic surfactant sodium bis(2-ethyl-1-hexyl)sulfosuccinate (AOT). It was apparent that the membrane components in whole cells were sufficient for optimal PAC production and no further surfactant addition is required for optimal performance.     

Role of pyruvate in enhancing pyruvate decarboxylase stability towards benzaldehyde

Biotransformation of benzaldehyde and pyruvate into (R)-phenylacetylcarbinol (PAC) catalysed by Candida utilis pyruvate decarboxylase (PDC) at low buffer concentration (20 mM MOPS) was enhanced by maintenance of neutral pH through acetic acid addition. PDC was very stable in this buffer (half-life 138 h at 6 degrees C), however a benzaldehyde emulsion (400 mM) caused rapid deactivation. The inclusion of 2M glycerol did not protect PDC from inactivation by benzaldehyde but initial rates were increased by 50% and the final PAC level was enhanced from 40 to 51 g l(-1). Low levels of by-products acetaldehyde (0.1-0.15 g l(-1)) and acetoin (1.1-1.3 g l(-1)) were formed in both the presence and absence of 2 M glycerol. Interestingly PDC was more stable towards benzaldehyde when pyruvate was present: no activity was lost during the first hour of biotransformation (2 M glycerol, benzaldehyde concentration decreased from 400 to 345 mM, pyruvate from 480 to 420 mM) but PDC was completely inactivated in less than 30 min when exposed to the same concentrations of benzaldehyde in the absence of pyruvate. Thus the enzyme in catalytic action was more stable than the resting enzyme.     

Influence of nutrients on growth and bacteriocin production by Leuconostoc mesenteroides L124 and Lactobacillus curvatus L442

The aim of this study was to investigate the effect of complex nutrients on microbial growth and bacteriocin production, in order to improve bacteriocin synthesis during the growth cycle of Leuconostoc mesenteroides L124 and Lactobacillus curvatus L442. The fermentations were conducted at the optimum pH and temperature for bacteriocin production (pH 5.5+/-0.1 and temperature 25+/-0.1 degrees C). Because of their association with the final biomass, conditions favouring the increase of the produced biomass resulted in the increase of bacteriocin activity in the growth medium. Since the produced final biomass and the final concentration of the bacteriocins were associated with the amount of the carbon (glucose) and nitrogen source, better growth of the lactic acid bacterial strains favoured the increase of the specific bacteriocin production. Additionally, the bacteriocin production was influenced by carbon/nitrogen ratio.     

Recombinant trypsin production in high cell density fed-batch cultures in Escherichia coli

Fed-batch techniques were employed to obtain high cell density cultures (92-100 g DCW/L) of Escherichia coli strain X90 producing a recombinant serine protease, rat anionic trypsin, secreted to the periplasm. The specific growth rate was controlled to minimize growth-inhibiting acetate formation by utilizing an exponential feeding profile determined from mass balance equation. The volumetric yield of recombinant rat anionic trypsin was 56 mg/L, and the final cell density was 92 g DCW/L when the culture was induced in the late logarithmic phase. However, when the culture was induced in the early logarithmic phase, the volumetric yield was 13 mg/L and the final cell density was 14 g DCW/L. Thus, the induction timing is shown to have a significant effect on the final cell density as well as the overall volumetric yield of the recombinant protease. (c) 1993 Wiley & Sons, Inc.