Comparison of photobioreactors and optimal light regime for rapid vegetative propagation of transgenic Undaria pinnatifida gametophytes

BACKGROUND: Previously, tachyplesin gene (tac) has been successfully transferred into Undaria pinnatifida gametophytes using the method of microprojectile bombardment transformation. The objectives of this study were to compare and evaluate the performance of bubble‐column and airlift bioreactors to determine a preferred configuration of bioreactor for vegetative propagation of transgenic U. pinnatifida gametophytes, and to then investigate the influence of light on vegetative propagation of these gametophytes, including incident light intensity, photoperiod and light quality to resolve the problems of rapid vegetative propagation within the selected bioreactor. RESULTS: Experimental results showed that final dry cell density in the airlift bioreactor was 12.7% higher than that in the bubble‐column bioreactor under the optimal aeration rate of 1.2 L air min^?1 L^?1 culture. And a maximum final dry cell density of 2830 mg L^?1 was obtained within the airlift bioreactor using blue light at 40 µmol m^?2 s^?1 with a light/dark cycle of 14/10 (h). Polymerase chain reaction (PCR) analysis indicated that genes (bar and tac) were not lost during rapid vegetative propagation within the airlift bioreactor. CONCLUSION: The airlift bioreactor was shown to be much more suitable for rapid vegetative propagation of transgenic U. pinnatifida gametophytes than the bubble‐column bioreactor in the laboratory. The use of blue light allows improvement of vegetative propagation of transgenic U. pinnatifida gametophytes. Copyright © 2009 Society of Chemical Industry     

Potential fuel oils from the microalga Choricystis minor

BACKGROUND: Continuous culture of the freshwater microalga Choricystis minor was investigated for possible use in producing lipid feedstock for making biofuels. The effects of temperature (10–30 °C) and dilution rate (0.005–0.017 h^?1) on lipid productivity in a nutrient sufficient medium in a 4 L stirred tank bioreactor under continuous illumination at an incident irradiance level of 550 µE · m^?2s^?1 and a controlled pH of 6 under carbon dioxide supplemented conditions are reported. RESULTS: The maximum lipid productivity was 82 mg L^?1 d^?1 at 25 °C and a dilution rate of 0.014 h^?1. Lipid contents of the biomass were 21.3 ± 1.7 g per 100 g of dry biomass, irrespective of the culture temperature and dilution rate. After the biomass had been grown in nutrient sufficient conditions in continuous culture, it was recovered and subjected to various postharvest treatments. With the best postharvest treatment, the neutral lipid contents of the algal biomass were raised ～6‐fold relative to untreated biomass. CONCLUSION: At 82 mg L^?1 d^?1, or 21 000 L ha^?1 year^?1, the lipid productivity of C. minor was nearly four times the lipid productivity of oil palm, a highly productive crop. Therefore, C. minor is potentially a good source of renewable lipid feedstock for biofuels. Copyright © 2009 Society of Chemical Industry     

Continuous production of poly‐β‐hydroxybutyrate by high‐cell‐density cultivation of Wautersia eutropha

BACKGROUND: Poly‐β‐hydroxybutyrate (PHB) accumulation is triggered by limitation of a nutrient other than carbon. The production cost of PHB is very high. In order to reduce this cost, continuous cultivation for the accumulation of PHB was investigated. The culture was first allowed to grow under fed‐batch conditions to yield a significant increase in biomass and PHB accumulation. Thereafter this high‐cell‐density biomass containing PHB was allowed to grow and maintained under conditions of continuous cultivation so that the overall process could be simplified and economised. RESULTS: For continuous cultivation a medium containing 90 g L^?1 fructose and 2.5 g L^?1 nitrogen (as urea) was fed continuously at a dilution rate of 0.1 h^?1. A steady state biomass of 27.7 g L^?1 with a PHB concentration of 5.5 g L^?1 was established in the bioreactor. This resulted in a continuous PHB productivity of 0.55 g L^?1 h^?1. CONCLUSION: The experiments have resulted in the development of a novel production technology involving the integration of batch, fed‐batch and continuous processes. At the same time the production of PHB under continuous cultivation increases the overall industrial importance of the system. Copyright © 2008 Society of Chemical Industry     

Growth promotive conditions for enhanced eritadenine production during submerged cultivation of Lentinus edodes

BACKGROUND: Mycelium of the medicinal mushroom shiitake, Lentinus edodes, is a potential source for production of the blood cholesterol reducing compound eritadenine. To increase the mycelial biomass and in turn the production of eritadenine, a potential growth promoting substance in the form of a water extract of distillers dried grains with solubles (DDGS) was added to the culture media. RESULTS: The hot water extract of DDGS was shown to considerably increase the growth of shiitake mycelia in bioreactor cultivations; the mycelial yield was 2–3 times higher than in the control, and the highest final biomass concentration obtained was 3.4 g L^?1. Further, by using shake flask cultures as inoculums the bioreactor cultivation time could be reduced by 1 week for some of the experiments. The highest final titer of eritadenine in the present study was 25.1 mg L^?1, which was about 2 times higher than in the control, and was also obtained when a water extract of DDGS was added to the culture medium. CONCLUSION: It was demonstrated that a water extract of DDGS promoted the growth of shiitake mycelia in bioreactor cultivations, along with enhanced eritadenine production. Copyright © 2012 Society of Chemical Industry     

Optimization of chromium removal by the chromium resistant mutant of the cyanobacterium Anacystis nidulans in a continuous flow bioreactor

BACKGROUND: Chromium removal potential of the cyanobacterium Anacystis nidulans and its chromium resistant strain Cr^rI8 has been optimized. Optimized parameters include biomass load, pH, temperature and dilution rate of the bioreactor. RESULTS: Results show that chromium resistant strain has high EC₅₀ dose for chromium compared to wild strain. Chromium removal potential of both strains is strongly influenced by various factors. Optimized conditions in batch system included pH 6.5, temperature 28 °C, biomass load 150 µg protein mL^?1 for 30 µmol L^?1 Cr⁶⁺ solution. In continuous flow bioreactor at optimum pH (6.5) and temperature (28 °C) at a fixed biomass of 10 mg protein and 30 µmol L^?1 Cr⁶⁺, metal removal efficiency varied with dilution rate. For A. nidulans continuous flow bioreactor, optimum dilution rate was 0.076 h^?1 (64.6 per cent metal removal) while for Cr^rI8 it was 0.152 h^?1 (85.8 per cent metal removal). Operative time of the Cr^rI8 bioreactor was also more (85 h) compared to A. nidulans bioreactor (45 h). CONCLUSION: Under optimized conditions resistant strain Cr^rI8 removed more Cr⁶⁺ compared to A. nidulans and thus has the potential to be exploited for Cr⁶⁺ removal from industrial effluents at large scale. Copyright © 2007 Society of Chemical Industry     

Kinetic modelling of lactic acid production from whey by Lactobacillus casei (NRRL B‐441)

The biomass growth, lactic acid production and lactose utilisation kinetics of lactic acid production from whey by Lactobacillus casei was studied. Batch fermentation experiments were performed at controlled pH and temperature with six different initial whey lactose concentrations (9‐77 g dm^?3) in a 3 dm³ working volume bioreactor. Biomass growth was well described by the logistic equation with a product inhibition term. In addition, biomass and product inhibition effects were defined with corresponding power terms, which enabled adjustment of the model for low‐ and high‐substrate conditions. The Luedeking‐Piret equation defined the product formation kinetics. Substrate consumption was explained by production rate and maintenance requirements. A maximum productivity of 2.5 g dm^?3 h^?1 was attained with an initial lactose concentration of 35.5 g dm^?3. Copyright © 2006 Society of Chemical Industry     

Biodegradation of diesel oil in a baffled roller bioreactor

BACKGROUND: Ex situ bioremediation is a feasible and economical way to remove petroleum pollutants from contaminated soil or water. A baffled roller bioreactor was shown to be effective for biodegradation of diesel oil as a model petroleum pollutant. Microorganisms enriched from an industrially contaminated soil with heavy hydrocarbons were shown to be the best inoculum source for diesel biodegradation. RESULTS: The baffled roller bioreactor demonstrated better performance than control (roller bioreactor without baffles) or bead mill roller (control bioreactor filled partially with spherical beads) bioreactors. Biodegradation consisted of both fast and slow stages for degradation of light and heavy compounds, respectively. Among the tested temperatures ranging from 15 to 35 °C, room temperature (23 °C) was found to be the optimum temperature for biodegradation. The values of maximum specific growth rate and substrate yield (µ_max and Y_XS) for the indigenous microorganisms in the baffled roller bioreactor at room temperature were found to be 0.72 ± 0.08 h^?1 and (7.0 ± 1.0) × 10⁷ cells mg^?1 diesel, respectively. Biodegradation of diesel concentrations up to 200 g L^?1 was achieved with the highest biodegradation rate of 266 mg L^?1 h^?1 at the highest rotation rate of 45 rpm in the baffled roller bioreactor. CONCLUSION: Using indigenous bacteria enriched from industrial contaminated soil at room temperature, a baffled roller bioreactor is able to biodegrade high diesel oil concentrations at high biodegradation rates. Copyright © 2008 Society of Chemical Industry     

Novel two‐in‐one bioreactor greatly improves lactic acid production from xylose by Lactobacillus pentosus

BACKGROUND: Simultaneous xylose isomerization and fermentation was investigated to improve the lactic acid production from xylose by Lactobacillus pentosus in a novel two‐in‐one bioreactor constructed by packing the immobilized xylose isomerase (65 g) in a fixed bed reactor (diameter 56 mm × 66 mm, packing volume 154 mL) with a permeable wall, which was installed inside a conventional fermenter (2 L) and rotated along the axis together with the mechanical stirrer of the fermenter. RESULTS: Xylose (20 g L^?1) was completely consumed within 24 h in the novel bioreactor, compared with 72 h needed for the control without packed enzyme. The maximum cell density (17.5 g L^?1) in the novel bioreactor was twice that in the control and the lactic acid productivity (0.58 g L^?1 h^?1) was 3.8 times higher. Repeated use of the immobilized enzyme showed that the lactic acid productivity and yield obviously dropped after the first batch fermentation but maintained almost unchanged afterwards. CONCLUSION: Simultaneous xylose isomerization and fermentation significantly improved lactic acid production from xylose by Lactobacillus pentosus. The novel bioreactor made it easier to recycle and reuse the immobilized enzyme. © 2012 Society of Chemical Industry     

Bio‐oxidation of ferrous ions by Acidithioobacillus ferrooxidans in a monolithic bioreactor

BACKGROUND: The bio‐oxidation of ferrous iron is a potential industrial process in the regeneration of ferric iron and the removal of H₂S in combustible gases. Bio‐oxidation of ferrous iron may be an alternative method of producing ferric sulfate, which is a reagent used for removal of H₂S from biogas, tail gas and in the pulp and paper industry. For practical use of this process, this study evaluated the optimal pH and initial ferric concentration. pH control looks like a key factor as it acts both on growth rate and on solubility of materials in the system. RESULTS: Process variables such as pH and amount of initial ferrous ions on oxidation by A. ferrooxidans and the effects of process variables dilution rate, initial concentrations of ferrous on oxidation of ferrous sulfate in the packed bed bioreactor were investigated. The optimum range of pH for the maximum growth of cells and effective bio‐oxidation of ferrous sulfate varied from 1.4 to 1.8. The maximum bio‐oxidation rate achieved was 0.3 g L^?1 h^?1 in a culture initially containing 19.5 g L^?1 Fe²⁺ in the batch system. A maximum Fe²⁺ oxidation rate of 6.7 g L^?1 h^?1 was achieved at the dilution rate of 2 h^?1, while no obvious precipitate was detected in the bioreactor. All experiments were carried out in shake flasks at 30 °C. CONCLUSION: The monolithic particles investigated in this study were found to be very suitable material for A. ferrooxidans immobilization for ferrous oxidation mainly because of its advantages over other commonly used substrates. In the monolithic bioreactor, the bio‐oxidation rate was 6.7 g L^?1 h^?1 and 7 g L^?1 h^?1 for 3.5 g L^?1 and 6 g L^?1 of initial ferrous concentration, respectively. For higher initial concentrations 16 g L^?1 and 21.3 g L^?1, bio‐oxidation rate were 0.9 g L^?1 h^?1 and 0.55 g L^?1 h^?1, respectively. Copyright © 2008 Society of Chemical Industry     

Bioremediation of toluene‐contaminated air using an external loop airlift bioreactor

An external loop airlift bioreactor (ELAB) has been used to capture and degrade toluene from a contaminated air stream. Using a spinning sparger, the toluene could be transferred from small, uniform bubbles into the aqueous culture media with an overall mass transfer coefficient as high as 1.1 h^?1. Due to the very volatile nature of toluene, Pseudomonas putida (ATCC 23973) was cultured and maintained on benzyl alcohol, the first intermediate compound in the metabolic degradation pathway for toluene. Consequently, before successful continuous operation of the ELAB with toluene‐contaminated air, Pseudomonas putida was acclimatized to toluene by using 30 min intermittent sparging of contaminated air into the bioreactor. Continuous sparging of toluene‐contaminated air could then be successfully carried out with 100% capture and biodegradation efficiency at a contaminated air concentration of 15 mg dm^?3 and a loading rate of 35 mg dm^?3 h^?1. Higher concentrations and loading rates were only partially degraded. Although this capture matches only the low rates reported earlier using biofilters to remediate toluene, the ELAB operates using submerged culture and requires no packing which can plug during biofilter operation. In this study, Pseudomonas putida grew on toluene at a maximum specific growth rate of only 0.05 h^?1. © 2003 Society of Chemical Industry     

Conversions of olive mill wastewater‐based media by Saccharomyces cerevisiae through sterile and non‐sterile bioprocesses

BACKGROUND: Olive mill wastewaters (OMWs) are an important residue and several methods have been proposed for their treatment. RESULTS: Remarkable decolorization (~63%) and phenol removal (~34% w/w) from OMW was achieved. In glucose‐based flask sterile cultures, enrichment with OMWs increased ethanol and biomass production compared with cultures without OMWs added. Flask sterile and un‐sterilized cultures demonstrated similar kinetic results. Batch‐bioreactor trials performed showed higher ethanol and lower biomass quantities compared with the respective shake‐flask experiments, while cultures used under un‐sterilized conditions revealed equivalent results to the sterile ones. In non‐sterile bioreactor cultures, OMWs addition enhanced biomass production in comparison with culture with no OMWs added, whereas ethanol biosynthesis was not affected. The maximum ethanol quantity achieved was 52 g L^?1 (conversion yield per sugar consumed of 0.46 g g^?1) in a batch bioreactor non‐sterilized trial with OMW–glucose enriched medium used as substrate, that presented initial reducing sugars concentration at ~115 g L^?1. Fatty acid analysis of cellular lipids demonstrated that in OMW‐based media, cellular lipids containing increased concentrations of oleic and linoleic acid were produced in comparison with cultures with no OMWs added. CONCLUSIONS: S. cerevisiae simultaneously produced bio‐ethanol and biomass and detoxified OMWs, under non‐sterile conditions. © 2012 Society of Chemical Industry     

Effects of butyric acid stress on anaerobic sludge for hydrogen production from kitchen wastes

BACKGROUND: Anaerobic digestion is an alternative technology to achieve the dual benefits of hydrogen production and waste stabilization from kitchen wastes. In this work, the butyric acid stress on anaerobic sludge was investigated in order to improve the tolerance of sludge against organic acids, and to enhance hydrogen accumulation. RESULTS: The tolerance of butyric acid in anaerobic sludge increased with the stress concentration, however, it decreased at concentrations greater than of 4.0 g L^?1. The maximum hydrogen yield reached 63.72 mL g^?1 VS at 4.0 g L^?1 stress, representing an increase of 114% compared with the control group. The concentration of volatile solids (VS) of the sludge and SCOD increased steadily with time up to 20 h. At 4.0 g L^?1 butyric acid stress, the maximum activity of β‐glucosidase, BAA‐hydrolysing protease and dehydrogenase enzyme were 14912.1 µmol PNP g^?1 TS h^?1, 134.14 µmol NH₄‐N g^?1 TS h^?1 and 7316.42 µg TF g^?1 TS h^?1, which were 2.78, 1.90 and 2.01 times that of the control, respectively. CONCLUSIONS: The feasibility of butyric acid stress on anaerobic sludge to increase hydrogen production from kitchen wastes was demonstrated. Remarkably, 4.0 g L^?1 butyric acid stress was found to be favorable for improving the tolerance of butyric acid in sludge as well as hydrogen yield in the experiment. Copyright © 2010 Society of Chemical Industry     

Fermentation and oxygen transfer characteristics in recombinant human growth hormone production by Pichia pastoris in sorbitol batch and methanol fed‐batch operation

BACKGROUND: The influence of methanol feed rate on recombinant human growth hormone (rhGH) production by Pichia pastoris hGH‐Mut⁺ in medium containing sorbitol was investigated at three different specific growth rates (µ), namely, 0.02 (MS‐0.02), 0.03 (MS‐0.03), and 0.04 (MS‐0.04). RESULTS: Increasing methanol feed rate above MS‐0.03 did not affect sorbitol consumption, showing that µ = 0.03 h^?1 is a threshold limiting value, above which sorbitol utilization became independent of methanol feed rate. Moreover, when sorbitol was consumed, no further cell growth was observed. Increase in methanol feed rate triggered cell synthesis and the highest cell concentration was obtained at MS‐0.04 as 48 g L^?1 (t = 18 h); whereas, the highest rhGH production, 270 mg L^?1, was obtained at MS‐0.03 as a consequence of lower extracellular protease production and higher AOX activity (41 U g^?1 CDW). Oxygen uptake rate increased with increasing µ, having the maximum value, 76.6 mmol m^?3 s^?1, at MS‐0.04. K_La had a tendency to increase with µ, having a maximum value of 0.15 s^?1 at MS‐0.04 (t = 15 h). CONCLUSION: By considering rhGH concentration and oxygen transfer characteristics, the bioprocess can be improved by a two‐stage feeding strategy, operating at MS‐0.04 at the beginning of fermentation, and thereafter shifting to MS‐0.03. Copyright © 2009 Society of Chemical Industry     

Improved cultivation conditions for polysaccharide production by H. influenzae type b

Haemophilus influenzae b (Hib), an encapsulated Gram‐negative cocco‐bacillus, is one of the most common agents of meningitis worldwide. The capsular polysaccharide conjugated to a carrier protein is the antigen of the vaccine against Hib. An optimized cultivation process that could lead to an increase in the polysaccharide production would be of great interest for mass vaccination programs. The aim of this work was to evaluate different culture conditions in attempt to improve the capsular polysaccharide yield. Hib was cultivated in a bioreactor with modified soy‐peptone and yeast‐extract (MP) medium and optimal hemin and nicotinamide adenine dinucleotide (NAD) concentration in the culture medium was established at 30 mg L^?1 and 15 mg L^?1, respectively. The batch experiments were carried out as follows: (a) overlay aeration without pH control; (b) air‐sparged with dissolved oxygen tension (DOT) controlled at 10 and 30% air saturation, with and without pH control. The cultures with air‐sparged aeration, without pH control, showed values for the specific production (SP_p/x) of 180–190 mg PRP g^?1 dry cell weight (DCW) and overall polysaccharide productivity of 22–29 mg L^?1 h^?1, accounting for an increase of ca 47% over the polysaccharide production with overlay aeration. Batch cultivations with air sparged aeration led to an improvement in the poly(ribosylribitol phosphate) (PRP) production for both conditions (DOT at 10 and 30% air saturation) investigated upon pH control, achieving up to 980 PRP mg L^?1. The SP_p/x and overall polysaccharide productivity were 280–300 mg PRP g^?1 DCW and 45–41 mg L^?1h^?1, respectively. The best production of capsular polysaccharide was obtained in the modified MP‐medium, with 30 mg L^?1 hemin and 15 mg L^?1 NAD, upon sparged aeration and pH control. Copyright © 2005 Society of Chemical Industry     

Strategies of pH control and glucose‐fed batch fermentation for production of succinic acid by Actinobacillus succinogenes CGMCC1593

BACKGROUND: Succinic acid is an important precursor of numerous products, including pharmaceuticals, feed additives, green solvents, and biodegradable polymers. In this work, strategies of pH control and glucose‐fed batch fermentation for producing succinic acid using Actinobacillus succinogenes CGMCC1593 were carefully optimized. RESULTS: The production of succinic acid was stable within the pH range 6.0–7.2. Both cell growth and succinic acid production were inhibited by high concentrations of sodium and calcium ions, while there was no significant inhibition by magnesium ions. With an initial glucose concentration of 25 g L^?1, and glucose concentration was maintained between 10 and 15 g L^?1 during the course of fed batch fermentation, succinic acid concentration, productivity and yield were 60.2 g L^?1, 1.3 g L^?1 h^?1 and 75.1%, respectively. CONCLUSION: Of all the neutralization reagents used for pH control of A. succinogenes CGMCC1593, solid MgCO₃ was the most satisfactory. With increase of initial glucose concentration, the time course showed a longer growth lag period and the maximum biomass declined, while more carbon was diverted to succinate synthesis. The results obtained in this study should be helpful for the design of a highly efficient succinic acid production process. Copyright © 2008 Society of Chemical Industry     

Biodegradation of phenol-polluted air using an external loop airlift bioreactor

Biological air treatment methods are an alternative to conventional treatment methods such as activated carbon adsorption and chemical scrubbing. An external loop airlift bioreactor has been utilized to treat phenol-contaminated air using Pseudomonas putida. Saturated air was found to be cleansed of phenol below the detectable limit because of the high mass transfer rate of the pollutant from the air and the high growth rate of Pseudomonas putida. The bioreactor was found to degrade over 99% of the inlet phenol at rates from 21·5 to 194 mg h^?1 at concentrations between 650 and 850 mg m^?3 of air. A model of the system is developed based on an initial transient period followed by a pseudo-steady state period. The simulations compared well with the experimental data.     

Anthracene Biodegradation by Oleaginous Rhodococcus opacus for Biodiesel Production and Its Characterization

This study examined biodegradation of anthracene, a model low molecular weight polycyclic aromatic hydrocarbon (PAH) by oleaginous Rhodococcus opacus for biodiesel production. Specific biomass growth rate (µ) in the range of 0.0075–0.0185 h^?1 could be attained over the initial anthracene concentration (50–500 mg L^?1), along with 68–70.6% (w/w) lipid accumulation. 10% (v/v) inoculum size showed more positive effect than 5% (v/v) inoculum size on both anthracene biodegradation efficiency and lipid accumulation by R. opacus. ¹H and ¹³C nuclear magnetic resonance (NMR) spectroscopy of the bacterial lipids revealed 82.25% saturated fatty acids content. Furthermore, the transesterified bacterial lipids predominantly consisted of methyl palmitate (32.4%) and methyl stearate (25.9%) as the major fatty acid methyl esters (FAMEs). Overall, this study revealed a very good potential of the bacterium for the production of biodiesel from PAH-containing wastewater.     

Effects of light quality on the accumulation of oil in a mixed culture of Chlorella sp. and Saccharomyces cerevisiae

BACKGROUND: Chlorella strains rather than terrestrial oil crops having higher oil content and shorter generation time have been considered as promising candidates for alternative biodiesel. Since the influence of light quality on oil formation of microalgae in either monoculture or mixed culture has been shown to be either inconsistent or ambiguous, a light‐emitting diode (LED) photo‐bioreactor with different light sources and intensities was used in this study to investigate a cost‐effective lipid production process. RESULTS: The oil accumulation in a mixed culture of Chlorella sp. and Saccharomyces cerevisiae was higher than that in the monoculture under the different light sources used. Results of the influence of light quality on the mixed culture indicated that the optimal light wavelength and intensity for biomass formation was red LED light at 1000 lux, whereas the optimum for oil formation was blue LED light at 1000 lux. A novel two‐stage LED photo‐bioreactor was thus proposed and the highest P_max and productivity in this study were obtained as 261 mg L^?1 and 8.16 mg L^?1 h^?1, respectively. CONCLUSION: A novel two‐stage LED photo‐bioreactor using a mixed culture to optimize microalgal oil production was proposed and successfully demonstrated in this study. Copyright © 2011 Society of Chemical Industry     

The fermentation of mixtures of D‐glucose and D‐xylose by Candida shehatae,Pichia stipitis or Pachysolen tannophilus to produce ethanol

The fermentation of mixtures of D ‐glucose and D ‐xylose by three non‐traditional yeasts: Candida shehatae (ATCC 34887), Pachysolen tannophilus (ATCC 32691) and Pichia stipitis (ATCC 58376) have been studied to determine the optimal strain and initial culture conditions for the efficient production of ethanol. The comparison was made on the basis of maximum specific growth rate (µ_m), biomass productivity, the specific rates of total substrate consumption (q_s) and ethanol production (q_E) and the overall yields of ethanol and xylitol. All the experiments were performed in stirred‐tank batch reactors at a temperature of 30 °C. The initial pH of the culture medium was 4.5. The highest values of µ_m (above 0.5 h^?1) were obtained with P stipitis in cultures containing high concentrations of D ‐xylose. All three yeasts consumed the two monosaccharides in sequence, beginning with D ‐glucose. The values of q_s diminished during the course of each experiment with all of the yeasts. The highest values of the specific rates of total substrate consumption and ethanol production were obtained with C shehatae (for t = 10 h, q_s and q_E were above 5 g g^?1 h^?1 and 2 g g^?1 h^?1, respectively), although the highest overall ethanol yields were fairly similar with all three yeasts, at around 0.4 g g^?1. © 2002 Society of Chemical Industry     

Beet molasses based exponential feeding strategy for thermostable glucose isomerase production by recombinant Escherichia coli BL21 (DE3)

BACKGROUND: The effects of pretreated beet molasses based feeding strategies on thermostable glucose isomerase (GI) production by recombinant Escherichia coli BL21 (DE3) pLysS were investigated. RESULTS: The thermostable GI encoding gene of Thermus thermophilus (xyl_A) was recombined with pRSETA vector, and the pRSETA::xyl_A obtained was transferred into E.coli BL21 (DE3) pLysS and used for GI production. The highest soluble GI activity was obtained at t = 30 h, as A = 16 400 U L^?1 (20.6 U mg^?1 protein) under molasses based fed‐batch operation, with a specific growth rate µ = 0.1 h^?1 (M‐0.1); on the other hand, the highest cell concentration was obtained at µ = 0.15 h^?1 operation as 9.6 g L^?1 at t = 32 h. The highest oxygen uptake was 4.57 mol m^?3 s^?1 at M‐0.1 operation. CONCLUSIONS: Molasses based fed‐batch operations were more successful in terms of cell concentration and thermostable enzyme production due to the existence of a natural sugar inducer, galactose, in the molasses composition. This study demonstrates the significance of proper feeding strategy development for over‐production of enzymes by recombinant E. coli strains. © 2012 Society of Chemical Industry