Production enhancement of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) in Halogeometricum borinquense,characterization of the bioplastic and desalination of the bioreactor effluent

Polyhydroxyalkanoates (PHAs) are a replacement of conventional single-use plastics. Bioprocess conditions of the extreme halophilic archaeon Halogeometricum borinquense strain RM-G1 were selected resulting in the synthesis of 66.80 ± 1.69 % PHA (of cell dry mass) in 72 h using glycerol and tryptone as carbon and nitrogen sources respectively, yielding volumetric productivity of 0.206 ± 0.006 gL⁻¹ h⁻¹ in a repeated batch process in a small-scale bioreactor where 20 % of the production medium was used as the inoculum for the subsequent batch. The purified PHA was characterized as poly(3-hydroxybutyrate-co-3-hydroxyvalerate) with 10.21 mol% 3-hydroxyvalerate content possessing glass transition temperature -12.6 °C, degradation temperature 285 °C, number average molecular weight 156,899 Da, weight average molecular weight 288,723 Da, polydispersity index 1.8 and melting temperatures 139.1 °C and 152.5 °C. Maximum (21.7 ± 0.6 L m^-2 h⁻¹) and average (17.2 ± 0.6 L m^-2 h⁻¹) flux values were their respective highest and crystallization time was its least (3.0 ± 0.16 h) when ΔT was 90 °C and polytetrafluoroethylene membrane was applied for desalination of the bioreactor effluent by Direct Contact Membrane Distillation. While using polyvinylidene fluoride membrane, maximum 25.5 ± 0.5 L m^-2 h⁻¹ and average 18.6 ± 0.2 L m^-2 h⁻¹ fluxes were obtained and crystallization time decreased (3.25 ± 0.16 h) even when ΔT was lowered by 20 °C.     

Unmarked insertional inactivation in the gfo gene improves growth and ethanol production by Zymomonas mobilis ZM4 in sucrose without formation of sorbitol as a by-product,but yields opposite effects in high glucose

Sorbitol, one of the main by-products of growth on high sucrose concentrations, is catalyzed by glucose-fructose oxidoreductase (GFOR, EC 1.1.99.28) in Zymomonas mobilis, which decreases the ethanol yield. In this study, an unmarked gfo mutant from Z. mobilis ZM4 was constructed using a site-specific FLP recombinase, and growth and ethanol production were evaluated with or without the addition of sorbitol to the media. The inactivation of gfo had contrasting effects in different substrates, especially at high concentrations. The maximum specific growth rate (μ_m) and theoretical ethanol yield value (Y_m) increased from 0.065 h⁻¹ and 60.56% to 0.094 h⁻¹ and 83.87% in 342 g/L sucrose, respectively. Conversely, in 200 g/L glucose, gfo inactivation decreased μ_m and Y_m from 0.15 h⁻¹ and 89.85% to 0.10 h⁻¹ and 67.59%, respectively, and prolonged the lag period from 16 h to 40 h. The addition of sorbitol slightly accelerated growth and sucrose hydrolysis by the gfo mutant in 342 g/L sucrose; however, addition of sorbitol restored the μ_m and Y_m of the gfo mutant in 200 g/L glucose to 0.14 h⁻¹ and 82.50%, respectively. Inactivation of gfo had a small effect on fructose utilization, and a positive one on mixture of glucose and fructose similar to that on sucrose. These results provide further understanding of the osmoregulation mechanisms in Z. mobilis and may help to exploit the biotechnological applications of this industrially important bacterium.     

Effects of green LED light and three stresses on biomass and lipid accumulation with two-phase culture of microalgae

The effects of wavelengths of light-emitting diode (LED), nitrate concentration, and salt concentration were evaluated for the two-phase culture of the microalgal species Phaeodactylum tricornutum, Dunaliella tertiolecta, and Isochrysis galbana on cell growth and lipid production. Blue LEDs produced the highest biomass of P. tricornutum at a nitrate concentration of 8 mg/L, reaching 0.97 g dcw/L with a specific growth rate (μ) of 0.047 h⁻¹, followed by I. galbana with 0.79 g dcw/L and μ = 0.040 h⁻¹ and D. tertiolecta with 0.55 g dcw/L and μ = 0.028 h⁻¹. Of the three microalgae, P. tricornutum had the highest specific growth rate of μ_max = 0.070 h⁻¹ and lowest saturation constant of K_s = 4.18 mg/L, resulting in fast cell growth. The highest lipid production was obtained under green LED wavelength stress on day 14, reaching 60.6% (w/w) of the dry cell weight among the three microalgae. The main fatty acids produced by the three microalgae were myristic acid (C14:0), palmitic acid (C16:0), oleic acid (C18:1), and arachidic acid (C20:0), which comprised 72.68%–84.16% (w/w) of the total fatty acids content under three stresses.     

Engineered Pseudomonas putida simultaneously catabolizes five major components of corn stover lignocellulose: Glucose,xylose, arabinose,p-coumaric acid,and acetic acid

Valorization of all major lignocellulose components, including lignin, cellulose, and hemicellulose is critical for an economically viable bioeconomy. In most biochemical conversion approaches, the standard process separately upgrades sugar hydrolysates and lignin. Here, we present a new process concept based on an engineered microbe that could enable simultaneous upgrading of all lignocellulose streams, which has the ultimate potential to reduce capital cost and enable new metabolic engineering strategies. Pseudomonas putida is a robust microorganism capable of natively catabolizing aromatics, organic acids, and D-glucose. We engineered this strain to utilize D-xylose by tuning expression of a heterologous D-xylose transporter, catabolic genes xylAB, and pentose phosphate pathway (PPP) genes tal-tkt. We further engineered L-arabinose utilization via the PPP or an oxidative pathway. This resulted in a growth rate on xylose and arabinose of 0.32 h⁻¹ and 0.38 h⁻¹, respectively. Using the oxidative L-arabinose pathway with the PPP xylose pathway enabled D-glucose, D-xylose, and L-arabinose co-utilization in minimal medium using model compounds as well as real corn stover hydrolysate, with a maximum hydrolysate sugar consumption rate of 3.3 g/L/h. After modifying catabolite repression, our engineered P. putida simultaneously co-utilized five representative compounds from cellulose (D-glucose), hemicellulose (D-xylose, L-arabinose, and acetic acid), and lignin-related compounds (p-coumarate), demonstrating the feasibility of simultaneously upgrading total lignocellulosic biomass to value-added chemicals.     

Concomitant wastewater treatment with lipid and carotenoid production by the oleaginous yeast Rhodosporidium toruloides grown on brewery effluent enriched with sugarcane molasses and urea

In this study, secondary brewery wastewater (SBWW) supplemented with sugarcane molasses (SCM) was used for SBWW treatment with concomitant lipid and carotenoid production by the yeast Rhodosporidium toruloides NCYC 921. In order to improve the biomass production, ammonium sulfate, yeast extract and urea were tested as nitrogen sources. Urea was chosen as the best low-cost nitrogen source. A fed-batch cultivation was carried out with SBWW supplemented with 10 g L⁻¹ of sugarcane molasses as carbon source, and 2 g L⁻¹ of urea as nitrogen source. A maximum biomass concentration of 42.5 g L⁻¹ was obtained at t = 126.5 h and the maximum biomass productivity was 0.55 g L⁻¹ h⁻¹ at t = 48.25 h. The maximum lipid content was 29.9 % w/w (DCW) at t = 94 h of cultivation and the maximum carotenoid content was 0.23 mg g⁻¹ at 120 h of cultivation. Relatively to the SBWW treatment, after the batch phase, 45.8 % of total Kjeldahl nitrogen removal, 81.7 % of COD removal and 100 % of sugar consumption were observed. Flow cytometry analysis revealed that 27.27 % of the cells had injured membrane after the inoculation. This proportion was reduced to 10.37 % at the end of the cultivation, indicating that cells adapted to the growth conditions.     

Optimization of growth and production of toxins by three dinoflagellates in photobioreactor cultures

A bioreactor system for biotoxin production was appraised against traditional methods of growing dinoflagellate cultures. In an optimised bioreactor culture (5.4?L) operated in batch mode, growth of Karenia selliformis was more efficient than in 15-L bulk carboy culture in terms of growth rate (μ?=?0.07?day^?1 versus 0.05?day^?1) and growth maximum (G _max, 169.10⁶ versus 41.10⁶ cells L^?1). Maximal gymnodimine concentration (1200?μg L^?1) in bioreactor culture was 8-fold higher than in bulk carboy culture, and the yield per cell (pg cell^?1) was 2-fold higher. Similarly the bioreactor batch culture of Alexandrium ostenfeldii performed more efficiently than carboy cultures in terms of growth rate (1.6-fold higher), growth maximum (15-fold higher) and desmethyl C spirolide (SPX-desMe-C) yield (5-fold higher [μg L^?1], though the yield [pg cell^?1basis] was lower). When bioreactor cultures of K. selliformis were operated in continuous mode, the yield of gymnodimine was substantially higher than a carboy or the bioreactor run in batch mode to growth max (793?μg day^?1 over 58?days in continuous culture was achieved versus an average of 60?μg day^?1 [carboy over 40?days] or 249?μg day^?1 [batch mode] over 26?days). Likewise in continuous bioreactor cultures of A. ostenfeldii run over 25?days, the yield of SPX-desMe-C (29?μg day^?1) was substantially higher than in same cultures run in batch mode or carboys (10.2 day^?1 and 7.7?μg day^?1 respectively). Similarly 5.4?L bioreactor batch cultures of K. brevisulcata reached 3.8-fold higher cell densities than carboy cultures, and when operated in continuous mode, the brevisulcatic acids were more efficiently produced than in batch culture (12?μg day^?1 versus 7?μg day^?1). When the bioreactor system was upscaled to 52?L, the maximum cell densities and toxin yields of K. brevisulcata cultures were somewhat less than those achieved in the smaller reactor, which was attributed to reduced light penetration.     

Lactic acid production with Lactobacillus casei ssp. rhamnosus NBIMCC 1013: Modeling and optimization of the nutrient medium

The medium needed to perform a fermentation process with viable cells of Lactobacillus casei ssp. rhamnosus NBIMCC 1013 for the production of lactic acid was modeled and optimized. On the basis of single‐factor experiments and statistical analysis, the significant factors affecting the fermentation process, i.e. the concentration of carbon source, concentrations of both yeast and meat extracts, and the range of variability of these components were determined. Modeling and optimization of the medium contents were performed using central composite design. The composition of the medium used for the production of lactic acid (g/L) was as follows: glucose 69.8, meat extract 17.07, yeast extract 10.9, CH₃COONa 10, K₂HPO₄ 0.25, KH₂PO₄ 0.25, MgSO₄·7H₂O 0.05, and FeSO₄ 0.05. The maximum specific growth rate of the lactic acid bacteria (μ=0.51 h⁻¹) and other kinetic parameters were determined during cultivation in a laboratory bioreactor using the logistic equation and the Luedeking–Piret model. The obtained medium allows the production of lactic acid under optimum conditions, at high specific sugar assimilation rates and high lactic acid accumulation rates. The positive results of the paper are the new nutrient medium for lactic acid production and the process kinetic model, enabling scaling up and switching to a continuous process.     

Production and scale‐up of a monoclonal antibody against 17‐hydroxyprogesterone

The hybridoma 192 was used to produce a monoclonal antibody (MAb) against 17‐hydroxyprogesterone (17‐OHP), for possible use in screening for congenital adrenal hyperplasia (CAH). The factors influencing the MAb production were screened and optimized in a 2 L stirred bioreactor. The production was then scaled up to a 20 L bioreactor. All of the screened factors (aeration rate, stirring speed, dissolved oxygen concentration, pH, and temperature) were found to significantly affect production. Optimization using the response surface methodology identified the following optimal production conditions: 36.8°C, pH 7.4, stirring speed of 100 rpm, 30% dissolved oxygen concentration, and an aeration rate of 0.09 vvm. Under these conditions, the maximum viable cell density achieved was 1.34 ± 0.21 × 10⁶ cells mL^?1 and the specific growth rate was 0.036 ± 0.004 h^?1. The maximum MAb titer was 11.94 ± 4.81 μg mL^?1 with an average specific MAb production rate of 0.273 ± 0.135 pg cell^?1 h^?1. A constant impeller tip speed criterion was used for the scale‐up. The specific growth rate (0.040 h^?1) and the maximum viable cell density (1.89 × 10⁶ cells mL^?1) at the larger scale were better than the values achieved at the small scale, but the MAb titer in the 20 L bioreactor was 18% lower than in the smaller bioreactor. A change in the culture environment from the static conditions of a T‐flask to the stirred bioreactor culture did not affect the specificity of the MAb toward its antigen (17‐OHP) and did not compromise the structural integrity of the MAb. © 2012 American Institute of Chemical Engineers Biotechnol. Prog., 2013     

Immobilization of Kluyveromyces marxianus cells containing inulinase activity in open pore gelatin matrix: 2. Application for high fructose syrup production

Batch and continuous production of high fructose syrup from Jerusalem artichoke tubers has been studied using yeast cells immobilized in open pore gelatin matrix. In a batch reactor, the hydrolysis was 93% ($\text{d}\text{-fructose/}\text{d}\text{-glucose}\text{= 90/10}$) and 42 mg d-fructose per ml was produced from the artichoke tuber extract by immobilized cells in 3 h. The same immobilized cells were recycled and used repeatedly for 10 batch cycles starting with fresh juice at the beginning of each cycle. It was found that immobilized cells were extremely stable and the percent hydrolysis was almost constant for all 10 batch cycles. In a continuous reactor using an immobilized cell concentration of 65.7 g (dry wt) l^?1 of total working bioreactor volume, the percent hydrolysis was found to remain constant at ～100% at dilution rates <1.26 h^?1, but beyond that it decreased. Volumetric productivity attained its maximum value at D = 2.08 h^?1 and was found to be 100 g l^?1 h^?1. This was achieved at a feed sugar conversion of 80%. At 90% conversion and D = 1.66 h^?1, the productivity was found to be 90 g l^?1 h^?1. Continuous operation of the immobilized cell bioreactor at a constant dilution rate of 1.65 h^?1 for 240 h resulted in only 2% loss of original activity.     

Protective role of Punica granatum L. peel extract against oxidative damage in experimental diabetic rats

Punica granatum L. (Punicaceae) peels extract had the highest free radical scavenging capacity among the tested medicinal plants which are being used traditionally for treatment of diabetes in Jordan. Accordingly, the present study aimed to investigate the antioxidant effect of P. granatum peel methanolic extract against oxidative damage in streptozotocin-induced diabetic rats. The antioxidant activity of P. granatum peel extract was investigated by examining the level of antioxidant enzymes, catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPx), glutathione-S-transferase (GST) and glutathione reductase (GR), the serum total antioxidant capacity and lipid peroxidation in the tissues of treated diabetic rates comparing with normal and untreated diabetic ones. The results revealed that intraperitoneal administration of 10 and 20 mg kg⁻¹ (body weight) of P. granatum peel extract for 4 weeks significantly enhanced the activities of antioxidant enzymes in liver, kidney and RBC of STZ-induced diabetic rats. The extract also caused a significant reduction in malondialdehyde (MDA), a lipid peroxide's marker, in diabetic rat tissues and elevated the total serum antioxidant capacity in dose-dependent manner. In conclusion, this study clearly showed that P. granatum peel extract has protective role against the oxidative damage in STZ-induced diabetic rats.     

High ethanol productivities using small Ca-alginate beads of immobilized cells of Zymomonas mobilis

Summary Zymomonas mobilis cells were immobilized into small 1 mm diameter beads of Ca-alginate in order to minimize mass transfer limitations and maximize immobilized cell activity. A combination of small bead size with a high cell concentration of 58 g dry wt. cell per lit. bead volume resulted in high ethanol productivities using a newly designed packed bed bioreactor system. Steady-state dilution rates ranging from 0.4 h^-1 to 3.9 h^-1 were run resulting in a maximum productivity of 102 g ethanol/l/h for an inlet substrate concentration of 100 g glu/l and 87% conversion. The bioreactor was run continuously at a fixed dilution rate for 384 h and short intermittent treatment of the beads with CaCl₂ temporarily increased ethanol productivity to a maximum of 116 g ethanol/l/h.     

Over-production of human interferon-γ by HCDC of recombinant Escherichia coli

A simple fed-batch process was developed using a modified variable specific growth rate feeding strategy for high cell density cultivation of Escherichia coli BL21 (DE3) expressing human interferon-gamma (hIFN-γ). The feeding rate was adjusted to achieve the maximum attainable specific growth rate during fed-batch cultivation. In this method, specific growth rate was changed from a maximum value of 0.55 h⁻¹ at the beginning of feeding and then it was reduced to 0.4 h⁻¹ at induction time.The final concentration of biomass and IFN-γ was reached to ∼115 g l⁻¹ (DCW) and 42.5 g(hIFN-γ) l⁻¹ after 16.5 h, also the final specific yield and overall productivity of recombinant hIFN-γ (rhIFN-γ) were obtained 0.37 g(hIFN-γ) g⁻¹ DCW and 2.57 g(hIFN-γ) l⁻¹ h⁻¹, respectively. According to available data this is the highest specific yield and productivity that has been reported for recombinant proteins production yet.     

Kinetics of growth and caffeine demethylase production of Pseudomonas sp. in bioreactor

The effect of various initial caffeine concentrations on growth and caffeine demethylase production by Pseudomonas sp. was studied in bioreactor. At initial concentration of 6.5 g l^?1 caffeine, Pseudomonas sp. showed a maximum specific growth rate of 0.2 h^?1, maximum degradation rate of 1.1 g h^?1, and caffeine demethylase activity of 18,762 U g CDW^?1 (CDW: cell dry weight). Caffeine degradation rate was 25 times higher in bioreactor than in shake flask. For the first time, we show highest degradation of 75 g caffeine (initial concentration 20 g l^?1) in 120 h, suggesting that the tested strain has potential for successful bioprocess for caffeine degradation. Growth kinetics showed substrate inhibition phenomenon. Various substrate inhibition models were fitted to the kinetic data, amongst which the double-exponential (R ² = 0.94), Luong (R ² = 0.92), and Yano and Koga 2 (R ² = 0.94) models were found to be the best. The Luedeking–Piret model showed that caffeine demethylase production kinetics was growth related. This is the first report on production of high levels of caffeine demethylase in batch bioreactor with faster degradation rate and high tolerance to caffeine, hence clearly suggesting that Pseudomonas sp. used in this study is a potential biocatalyst for industrial decaffeination.     

High cell density fed-batch fermentation for the production of a microbial lipase

Extracellular lipase of the yeast Candida rugosa was produced via high cell density fed-batch fermentations using palm oil as the sole source of carbon and energy. Feeding strategies consisted of a pH-stat operation, foaming-dependent control and specific growth rate control in different experiments. Compared to foaming-dependent feeding and the pH-stat operation, the specific growth rate control of feeding proved to be the most successful. At the specific growth rate control set at 0.05 h⁻¹, the final lipase activity in the culture broth was the highest at ∼700 U L⁻¹. This was 2.6-fold higher than the final enzyme activity obtained at a specific growth rate control set at 0.15 h⁻¹. The peak enzyme concentration achieved using the best foaming-dependent control of feeding was around 28% of the peak activity attained using the specific growth rate control of feeding at 0.05 h⁻¹. Similarly, the peak enzyme concentration attained using the pH-stat feeding operation was a mere 9% of the peak activity attained by specific growth rate control of feeding at a set-point of 0.05 h⁻¹. Fed-batch fermentations were performed in a 2 L stirred-tank bioreactor (30 °C, pH 7) with the dissolved oxygen level controlled at 30% of air saturation.     

2,3-Butanediol production using Klebsiella oxytoca ATCC 8724: Evaluation of biomass derived sugars and fed-batch fermentation process

For this study, 2,3-butanediol (BD) fermentation from pure and biomass-derived sugar were optimized in shake-flask and 5-L bioreactor levels using Klebsiella oxytoca ATCC 8724. The results showed that 70 g/L of single sugar (glucose or xylose) and 90 g/L of mixed-sugar (glucose:xylose = 2:1) were optimum concentrations for efficient 2,3-BD fermentation. At optimum sugar concentrations, 2,3-BD productivities were 1.03, 0.64 and 0.50 gL⁻¹ h⁻¹, and yields were 0.43, 0.36 and 0.35 g/g in glucose, xylose and mixed-sugar medium, respectively. The lack of simultaneous utilization of glucose and xylose led to the lowest productivity in the mixed-sugar medium. Detoxification of biomass hydrolyzates was necessary for efficient 2,3-BD fermentation when sugar concentrations in the medium was 90 g/L or higher, but not with sugar concentrations of 30 g/L or less. A fed-batch fermentation using glucose medium led to an increase 2,3-BD titer to 79.4 g/L and yields 0.47 g/g, while productivity decreased to 0.79 gL⁻¹ h⁻¹. However, the fed-batch process was inefficient using mixed-sugar and biomass hydrolyzates because of poor xylose utilization. These results indicated that appropriate biomass processing technologies must be developed to generate separate glucose and xylose streams to produce high 2,3-BD titer from biomass-derived sugar using a fed-batch process.     

Enhanced production of valienamine by Stenotrophomonas maltrophilia with fed-batch culture in a stirred tank bioreactor

Valienamine is an important medicinal intermediate with broad use in the synthesis of some stronger α-glucosidase inhibitors. In order to improve valienamine concentration in the fermentation broth and make the downstream treatment easy, a fed-batch process for the enhanced production of valienamine by Stenotrophomonas maltrophilia in a stirred tank bioreactor was developed. Results showed that supplementation of validamycin A in the process of cultivation could increase the valienamine concentration. One-pulse feeding was observed to be the best strategy. The maximum valienamine concentration of 2.35 g L⁻¹ was obtained at 156 h when 86.4 g of validamycin A was added to a 15-L bioreactor containing 8 L fermentation medium with one-pulse feeding. The maximum valienamine concentration had a great improvement and was increased above 100% compared to batch fermentation in the stirred tank bioreactor. The pH-controlled experiments showed that controlling the pH in the process of one-pulse feeding fermentation had not obvious effect on the production of valienamine.     

Optimizing l-(+)-lactic acid production by thermophile Lactobacillus plantarum As.1.3 using alternative nitrogen sources with response surface method

The effects of five alternative nitrogen sources, namely, malt sprout (MS), corn steep liquor (CSL), NH₄Cl, NH₄NO₃ and diamine citrate (DC) were investigated on the l-(+)-lactic acid (LA) production by thermophile Lactobacillus plantarum As.1.3. Through the statistical analysis of the results by three steps of response surface methodology (RSM) design, MS and CSL were found to have significant effects on the LA production and their optimal concentrations in the medium should be 16.0 g/L and 12.0 g/L, respectively. The verification of the optimized medium showed that the maximum specific growth rate (μ_m) was 1.09 h⁻¹, the cell yield coefficient (Y_X/S) and the l-(+)-lactic acid yield coefficient (Y_P/S) were 0.233 (OD₆₂₀/g) and 0.98 (g/g), and the maximum volumetric productivity and the average volumetric productivity were 13.0 g/L h and 3.20 g/L h, respectively. The results indicate that the LA production can also be enhanced with the inexpensive nitrogen source alternatives.     

Epoxidation of 1,7‐octadiene by Pseudomonas oleovorans in a membrane bioreactor

A growing cell culture of Pseudomonas oleovorans was used to biotransform 1,7‐octadiene to 1,2‐epoxy‐7,8‐octene in a continuous‐flow bioreactor with an external membrane module. A dense silicone rubber membrane was used to contact an organic phase, containing both the reactant (1,7‐octadiene) and the growth substrate (heptane), with an aqueous biomedium phase containing the biocatalyst. Heptane and octadiene delivery to the aqueous phase, and epoxide extraction into the solvent, occurred by diffusion across the dense membrane under a concentration‐driving force. In addition, a liquid feed of heptane and octadiene was pumped directly into the bioreactor to increase the rate of delivery of these compounds to the aqueous phase. In this system 1,2‐epoxy‐7,8‐octene accumulated in a pure solvent phase, thus, product recovery problems associated with emulsion formation were avoided. Furthermore, no phase breakthrough of either liquid across the membrane was observed. In this system, the highest volumetric productivity obtained was 30 U.L⁻¹, and this was achieved at a dilution rate of 0.07 h⁻¹, 70 m².m⁻³ of membrane area, and a steady‐state biomass concentration of 2.5 g.L⁻¹. The system was stable for over 1250 h. Decreasing the dilution rate led to an increased biomass concentration, however, the specific activity was significantly reduced, and therefore, an optimal dilution rate was determined at 0.055 h⁻¹. © 1999 John Wiley & Sons, Inc. Biotechnol Bioeng 63: 601–611, 1999.     

Enhancing yield of <Emphasis Type="Italic">S</Emphasis>-adenosylmethionine in <Emphasis Type="Italic">Pichia pastoris</Emphasis> by controlling NH<Subscript>4</Subscript><Superscript>+</Superscript> concentration

Yield of S-adenosylmethionine was improved significantly in recombinant Pichia pastoris by controlling NH₄ ⁺ concentration. The highest production rate was 0.248 g/L h when NH₄ ⁺ concentration was 450 mmol/L and no repression of cell growth was observed. Within very short induction time (47 h), 11.63 g/L SAM was obtained in a 3.7 L bioreactor.     

Removal of benzene in a hybrid bioreactor

A novel hybrid bioreactor was designed to remove volatile organic compounds from wastewater and its performance was investigated. The bioreactor was composed of a biofilter section and a bubble column bioreactor section. Benzene was used as a model compound and the influent benzene was removed by immobilized cells in a bubble column bioreactor. Gas phase benzene stripped by air injection was removed in a biofilter. When the superficial air flow rate was 21.1 m h⁻¹ (0.76 min of residence time in a biofilter), up to 2.2 ppm of benzene in gas phase was removed completely in a biofilter and the maximum removal rate was 4.71 mg day⁻¹ cm⁻³. The concentration profile of benzene along the biofilter column was dependent on the superficial air flow rate and the degree of microbial adaptation. Air flow rate and residence time were found to be the most important operation parameters for the hybrid bioreactor. By manipulating these operational parameters, the removal efficiency and capacity of the hybrid bioreactor could be enhanced. The organic load on the hybrid bioreactor could be shared by the biofilter and bubble column bioreactors and the fluctuation of load on the hybrid bioreactor could be absorbed by changing the distribution of benzene between biofilter and bubble column bioreactors. The maximum removal capacity of the hybrid bioreactor in the experimental range was obtained when the biofilter took 50.3% of influent benzene while 100% of removal efficiency was achieved when the biofilter took 72.3% of influent benzene.