Effect Of Oxygen Transfer Rate Research Articles

Co-production of Gluconic Acid and Fructo-oligosaccharides by Aureobasidium pullulans from Sugarcane Molasses: Effect of Oxygen Transfer Rate in Stirred Tank and Airlift Bioreactors

Aureobasidium pullulans NCYC 4012 was used to produce gluconic acid (GA) and fructo-oligosaccharides (FOS) from sugarcane molasses (ScM). For the first time, three types of bioreactors operating at different conditions of oxygenation—a stirred tank reactor (STR) operating under atmospheric pressure varying stirring rate, a pressurized STR under increased air pressure up to 4 bar of air, and an airlift reactor under atmospheric pressure varying aeration rate—were employed for GA and FOS biosynthesis by A. pullulans. The highest oxygenation conditions favored GA production in the three bioreactors, whereas the synthesis of FOS was not favored by high oxygen availability. GA yields close to 1 g·g−1 (grams of GA produced per grams of glucose consumed) were achieved in bioreactors under atmospheric pressure, and the highest titer of GA of 75 g·L−1 was obtained in the airlift bioreactor. In this last, the highest concentration of total FOS of 65 g·L−1 and yield of FOS of 0.58 g·g−1 were obtained.

Effect of oxygen transfer rate in stirred tank and air-lift bioreactors for Theobroma cacao cell culture

Effect of oxygen transfer rate in stirred tank and air-lift bioreactors for <i>Theobroma cacao</i> cell culture

Effects of oxygen transfer rate on the L(+) lactic acid production by Rhizopus oryzae NRRL 395 in stirred tank bioreactor

Lactic acid (LA) is a key product widely used in several industries and can be produced by aerobic microorganisms like the fungus Rhizopus oryzae NRRL 395. In this study, the effect of different oxygen transfer rates on the performance of R. oryzae was analyzed in a 3 L stirred tank bioreactor. Inoculum and sucrose initial concentrations were previously evaluated at the shake flask level in order to choose the initial culture conditions for the bioreactor trials. In bioreactor, evaluations showed a range of OTRmax between 0.13 and 0.28 kg m−3 h−1 and DOT of 72–83 %, in which were reached the best values of LA productivity (0.53 g L−1h−1), Yps (0.78–0.83 g g−1), and LA production (44 g L−1). Further, a dimensionless analysis determined that LA production is greater in Damköhler number (Da) ≈ 1 and effectiveness factor (ɳ) ≈ 0.14 conditions. Finally, these results were used in a comparative dimensionless analysis with other aerobic microbial systems reported in the literature. According to our knowledge, this is the first study in which the oxygen transfer/oxygen uptake relationships and their effects on R. oryzae are analyzed in-depth.

Individual effect of shear rate and oxygen transfer on clavulanic acid production by Streptomyces clavuligerus.

The production of biocompounds through the cultivation of filamentous microorganisms is mainly affected by Oxygen Transfer Rate (OTR) and shear rate ([Formula: see text]) conditions. Despite efforts have been made to evaluate the effect of operating variables (impeller speed, N; and airflow rate, ϕair) on clavulanic acid production, no analysis regarding the effect of OTR and [Formula: see text] was made. Then, the aim of this study was toevaluate the dissociated effect of physical phenomena suchas oxygen transfer and shear rate in the production of clavulanic acid from Streptomyces clavuligerus using a stirred tank bioreactor. Streptomyces clavuligerus cultivations were performed at five different OTR and [Formula: see text] conditions by manipulating the operating conditions (N, ϕair, and gas inlet composition). Cultivations performed at equal impeller speed (600rpm, similar [Formula: see text]) using oxygen enrichment, showed that CA productivity (ProdCA) was positively affected by OTR increase. Subsequently, the different shear conditions (achieved by varying the impeller speed) lead to an increase in CA production levels. Despite both OTR and shear rate positively enhanced CA productivity, [Formula: see text] exhibited the highest impact: an increase of 145% in OTRinitial enhanced the clavulanic acid productivity of about 29%, while an increment in the shear rate of 134% raised the ProdCA in 53%.

Optimized Bioconversion of Xylose Derived from Pre-Treated Crop Residues into Xylitol by Using Candida boidinii

Crop residues can serve as low-cost feedstocks for microbial production of xylitol, which offers many advantages over the commonly used chemical process. However, enhancing the efficiency of xylitol fermentation is still a barrier to industrial implementation. In this study, the effects of oxygen transfer rate (OTR) (1.1, 2.1, 3.1 mmol O2/(L × h)) and initial xylose concentration (30, 55, 80 g/L) on xylitol production of Candida boidinii NCAIM Y.01308 on xylose medium were investigated and optimised by response surface methodology, and xylitol fermentations were performed on xylose-rich hydrolysates of wheat bran and rice straw. High values of maximum xylitol yields (58–63%) were achieved at low initial xylose concentration (20–30 g/L) and OTR values (1.1–1.5 mmol O2/(L × h)). The highest value for maximum xylitol productivity (0.96 g/(L × h)) was predicted at 71 g/L initial xylose and 2.7 mmol O2/(L × h) OTR. Maximum xylitol yield and productivity obtained on wheat bran hydrolysate were 60% and 0.58 g/(L × h), respectively. On detoxified and supplemented hydrolysate of rice straw, maximum xylitol yield and productivity of 30% and 0.19 g/(L × h) were achieved. This study revealed the terms affecting the xylitol production by C. boidinii and provided validated models to predict the achievable xylitol yields and productivities under different conditions. Efficient pre-treatments for xylose-rich hydrolysates from rice straw and wheat bran were selected. Fermentation using wheat bran hydrolysate and C. boidinii under optimized condition is proved as a promising method for biotechnological xylitol production.

Enhanced production of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) biopolymer by recombinant Bacillus megaterium in fed-batch bioreactors.

Polyhydroxyalkanoates (PHAs) are biodegradable polyesters accumulated in a wide variety of microorganisms as intracellular carbon and energy storage compounds. Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) is one of the most valuable biopolymers because of its superior mechanical properties. Here, we developed a bioprocess utilizing recombinant Bacillus megaterium strain for PHBV over-production from glucose, without any precursor addition. PHA production was performed in a controlled bioreactor by batch and fed-batch modes using wild-type B. megaterium and rec-B. megaterium cells overexpressing the native phaC gene. The effect of oxygen transfer rate on biomass formation and PHA accumulation was also investigated, under different dissolved oxygen levels. Structural and thermal properties of PHA were characterized by GC-FID, 1H-NMR, TGA and DSC analyses. Significantly, the copolymer produced from glucose as the carbon source in rec-B. megaterium was composed of 58mol% of 3-hydroxyvalerate monomers. After 66h, rec-B. megaterium cells in fed-batch fermentation with a pre-determined growth rate µ0 = 0.1h-1 produced the highest CDW (7.7g L-1) and PHA concentration (6.1g L-1). Moreover, an exponential glucose feeding profile resulted in 2.2-fold increase in PHA yield compared to batch cultivation. Overall, this study paves the way to an enhanced biopolymer production process in B. megaterium cells, where the highest product yield on cell was obtained as YP/X = 0.8gg-1.

The role of dissolved oxygen content as a modulator of microbial polyhydroxyalkanoate synthesis.

Polyhydroxyalkanoates (PHAs) are a diverse class of bio-polymers synthesized by bacteria, usually during imbalanced growth conditions. Optimizing PHA productivity is highly dependent on the bioreactor oxygen transfer rate (OTR), which is an important consideration for process performance and economics, particularly with increasing scale. Relatively few in-depth studies are available regarding the effect of OTR and dissolved oxygen content (DOC) on PHA formation, synthesis rates, composition, and characteristics. This review examines past research studies on the effect of low DOC environments on production of short-chain length (scl-) PHAs, synthesized by both pure and mixed cultures, in order to identify opportunities and gaps concerning the effect of DOC on production of medium-chain length (mcl-) PHAs, an area that has not been studied in detail. The literature indicates that production of scl-PHA (a reductive process) acts as an electron sink allowing cells to maintain balanced redox state at low DOC. Conversely, production of mcl-PHA via fatty acid de novo synthesis (also a reductive process) does not occur to any significant extent in low DOC environments, while mcl-PHA synthesis from fatty acids (an oxidative process) can be promoted in low DOC environments. The monomer composition, molecular mass, as well as physical and thermal properties of the polymer can change in response to OTR, but further research in this area is required for both scl- and mcl-PHAs. Process design and management of bioreactor OTR in PHA production might therefore be directed by the final application of the polymer rather than cost considerations.

Optimization of Surfactin Production by Bacillus subtilis ATCC 6633 in a Miniaturized Bioreactor

In recent years, biosurfactants due to wide applications in chemical, petroleum, food andpharmaceutical industries, have been widely considered by researchers. Biosurfactants are produced by aseries of microorganisms, so it is important to screen culture medium and operating conditions in miniaturized bioreactors prior to scaling up to large bioreactors.In this study, using a kind of miniaturized bioreactor called ventilation flask, optimal production conditions, including filling volume and shaking frequency to produce a surfactin-type biosurfactant by Bacillus subtilis ATCC 6633, were examined. Moreover, the effect of oxygen transfer rate (OTR) on the surfactin production was investigated according to Amoabediny and Buchs model. The results indicated that the maximum biomass and biosurfactant yield which obtained under optimal conditions (filling volume of 15 mL and shaking frequency of 300 rpm) were evaluated 0.3 g/L/h and 0.0485 g/L/h, respectively. Also, at the same conditions, the amount of surface tension decreased from 60.5 mN/m to 31.7 mN/m and the maximum oxygen transfer rate (OTRmax) obtained as 0.01 mol/L/h.

Influence of oxygen transfer rate on the accumulation of poly(3-hydroxybutyrate) by Bacillus megaterium

Poly(3-hydroxybutyrate)—P(3HB)—is a natural biodegradable polyester synthesized by several bacteria, produced from renewable resources. The effects of oxygen transfer rate on the intracellular accumulation of P(3HB) was evaluated, aiming at increasing P(3HB) synthesized by Bacillus megaterium DSM 32T in bioreactor batch cultures. Bench-scale bioreactor cultivations were performed under different volumetric oxygen mass transfer coefficients, kLa, setting stirrer speed on specified values. The results of this work show that oxygen transfer is a key factor on P(3HB) accumulation by B. megaterium, increasing the P(3HB) intracellular mass fraction from 39% to 62% of CDW at kLa condition of 0.006s−1.

Respiration activity monitoring system (RAMOS), an efficient tool to study the influence of the oxygen transfer rate on the synthesis of lipopeptide by Bacillus subtilis ATCC6633

The effect of oxygen transfer rate (OTR) on the synthesis of mycosubtilin, a non ribosomal lipopeptide antifungal biosurfactant, was investigated in the respiration activity monitoring system (RAMOS) for two Bacillus subtilis strains. These cultures were performed under definite oxygen-limited conditions without the adding of any anti-foam in the culture medium. By using four different filling volumes (FV) in the shaken bioreactors, different levels (20, 14, 9 and 7 mmol O 2 l −1 h −1) of oxygen-limited growth could be obtained. A 25-fold increase of the specific productivity of mycosubtilin was observed for B. subtilis ATCC6633 in the case of the most severe oxygen limitation. But nearly no effect could be found with strain BBG100 carrying the constitutive P repU promoter instead of the natural P myc promoter. Transcript analysis of the fenF gene belonging to the myc operon indicated that the P myc promoter regulation could be slightly oxygen sensitive. Additionally, different patterns of the synthetised mycosubtilin homologues were obtained for different level of oxygen-limited growths. At the present state of investigation, oxygen regulation was thus shown to act at different levels suggesting the existence of a complex regulatory system of NRPS lipopeptide synthesis in the natural B. subtilis ATCC6633 strain.

Bioreactor design for enhanced carrier-assisted surfactin production with Bacillus subtilis

Bacillus subtilis ATCC 21332 was used to produce a lipopeptide-type biosurfactant (namely, surfactin) in an innovative bioreactor tailored to solve the problems of severe foaming arising from production of the biosurfactant. To cope with the rapid foam generation, a conventional jar fermentor was integrated with a foam collector, a cell recycler, and a surfactin precipitation unit. Meanwhile, solid carriers (e.g., activated carbon) were added into the fermentation broth to increase cell mass concentration and surfactin yield. The proposed bioreactor allowed stable and efficient surfactin fermentation under intensive foaming conditions without the need of adding antifoam agents. The effect of oxygen transfer rate and mass transfer efficiency on surfactin production was also explored by employing various combinations of aeration and agitation rates. The best combination was 1.5 vvm and 300 rpm, giving an excellent maximum production rate, overall production rate, surfactin concentration, and surfactin yield of 190 mg L −1 h −1, 106 mg L −1 h −1, 6.45 g L −1, and 161 mg surfactin (g glucose) −1, respectively. It was also found that the oxygen volumetric mass transfer coefficient ( K L a) was highly correlated with the performance of surfactin production. The highest surfactin productivity was achieved when the fermentation was carried out at a K L a value of 0.0132 s −1.

Effect of oxygen transfer rate on β-carotene production from synthetic medium by Blakeslea trispora in shake flask culture

The effect of oxygen transfer rate (OTR) on β-carotene production by Blakelsea trispora in shake flask culture was investigated. The results indicated that the concentration of β-carotene (704.1 mg/l) was the highest in culture grown at maximum OTR of 20.5 mmol/(l h). In this case, the percentage of zygospores was over 50.0% of the biomass dry weight. On the other hand, OTR level higher than 20.5 mmol/(l h) was found to be detrimental to cell growth and pigment formation. To elucidate the effect of oxidative stress on β-carotene synthesis, the accumulation of hydrogen peroxide during fermentation under different OTRs was determined. A linear response of β-carotene synthesis to the level of H 2O 2 was observed, indicating that β-carotene synthesis is stimulated by H 2O 2. However, there was an optimal concentration of H 2O 2 (2400 μM) in enhancing β-carotene synthesis. At a higher concentration of H 2O 2, β-carotene decreased significantly due to its toxicity.

Effect of oxygen transfer rate on levels of key enzymes of xylose metabolism in Debaryomyces hansenii

The titers of key enzymes of xylose metabolism were measured and correlated with the kinetics of xylitol production by Debaryomyces hansenii under different oxygen transfer rates (OTR) in a batch reactor. An OTR change from 2.72 to 4.22 mmol O 2 l −1 min −1 resulted in a decrease in NADPH-dependent xylose reductase (XR) and NAD ± -dependent xylitol dehydrogenase (XDH) activities. For higher values of OTR (12.93 mmol O 2 l −1 min −1, the XDH titer increased twofold whereas the XR titer did not show a significant change. At the lowest OTR (2.72 mmol O 2 l −1 min −1), xylitol (and ethanol) production rates showed the highest values. However, xylitol specific productivity was twice as high as ethanol specific productivity. The titer of the NADPH-forming enzyme, glucose-6-phosphate dehydrogenase (GPDH), increased from 333 to 412 mU mg −1 when the OTR was increased. However, 6-phosphogluconate dehydrogenase (PGDH) activity remained unchanged and at a lower level, which indicates that this enzyme is responsible for the carbon flux control of the oxidative branch of the pentose phosphate pathway. The activity of the alcohol-forming enzyme was repressed at the higher amount of oxygen, decreasing its activity more than 50%. The changes in ADH suggested that two different metabolic regions under oxygen-limited conditions can be hypothesized for xylose metabolism by D. hansenii. For low OTR values (up to 4.22 mmol O 2 l −1 min −1), a fermentative-type activity is displayed. At higher OTR values (above 4.22 mmol O 2 l −1 min −1), no significant fermentative activity is reported.

Effects of aeration on extracellular dextransucrase production by Leuconostoc mesenteroides

The effect of oxygen transfer rate on extracellular dextransucrase production by Leuconostoc mesenteroides in batch fermentation without pH control was studied. The optimum aerobic conditions for both growth and dextransucrase formation were found to be at an oxygen transfer rate of about 1.0 mmol l −1 h −1.

Alcoholic fermentation of glucose and xylose by Pichia stipitis, Candida shehatae, Saccharomyces cerevisiae and Zymomonas mobilis: oxygen requirement as a key factor

To investigate simultaneous alcoholic fermentation of glucose and xylose derived from lignocellulosic material by separate or co-culture processes, the effect of oxygen transfer rate (OTR) on the fermentation of 50 g/l xylose by Pichia stipitis NRRL Y 7124 and Candida shehatae ATCC 22984, and the fermentation of 50 g/l glucose by Saccharomyces cerevisiae CBS 1200 and Zymomonas mobilis ATCC 10988 was carried out in batch cultures. The kinetic parameters of the xylose-fermenting yeasts were greatly dependent on the OTR. The optimum OTR values were found to be 3.9 and 1.75 mmol·1−1·h−1 for C. shehatae and P. stipitis, respectively. By contrast the fermentative parameters of S. cerevisiae were poorly affected by the OTR range tested (0.0–3.5 mmol·l−1·h−1) Under these conditions the ethanol yields ranged from 0.41 g·g−1 to 0.45 g·g−1 and the specific ethanol productivity was around 0.70 g·g−1·h−1. Z. mobilis gave the highest fermentative performance under strictly anaerobic conditions (medium continually flushed with nitrogen): under these conditions, the ethanol yield was 0.43 g·g−1 and the average specific ethanol productivity was 2.3 g·g−1·h−1. Process considerations in relation to the effect of OTR on the fermentative performance of the tested strains are discussed.

Fermentation of D‐xylose, D‐glucose, L‐arabinose mixture by Pichia stipitis: Effect of the oxygen transfer rate on fermentation performance

This article attempts to study the effect of oxygen transfer rate on the kinetic and stoichiometric parameters during the ethanol production from a sugar mixture by Pichia stipitis Y7124. The sugar mixture, with D-xylose as the major component, was a model sugar mixture of a hemicellulosic-derived hydrolysate from cereal straw

Effect of oxygen transfer rate on the composition of the pectolytic enzyme complex of Aspergillus niger

AbstractOptimal agitation and aeration conditions [assuring O2 transfer rates (OTR) from 12 to 179 mmol L−1 h−1] were determined for pectin lyase (PL) synthesis of an Aspergillus niger strain. Components of the pectolytic enzyme complex were also investigated in order to determine whether their O2 demand is identical with or different from that of pectin lyase. Should the latter be the case, a possibility would be given to produce enzyme complexes of different agitation and aeration conditions. According to our results, mycelium yield of Aspergillus niger attained a maximum at an OTR of 100 mmol L−1 h−1. The yields of the various pectolytic enzymes reached maxima at different OTRs. Pectin lyase production was the highest (0.555 µmol min−1 mL−1) at an OTR of 60 mmol L−1 h−1. Endopolygalacturonase (PG) production showed a maximum at the OTR of 49 mmol L−1 h−1 with a second peak at 100−135 mmol O2 L−1 h−1. Pectin esterase (PE) synthesis showed a maximum at on OTR of 12−14 mmol L−1 h−1, while both apple juice clarifying and macerating activities gave two maxima at 14 and 60 mmol L−1 h−1 due to the optima of PE and endo‐PG. Macerating activity showed a high value at OTR optimal for PL production as well.

Effect of oxygen-transfer rate on production of L-asparaginase by Erwinia aroideae.

A variety of aeration and agitation conditions were used to investigate the oxygen demand of Erwinia aroideae for growth and L-asparaginase production in a 14-liter fermenter. Maximum L-asparaginase activity of 4.25 IU/ml was obtained when the fermentation medium was aerated at 0.5 volumes air per volume medium per minute and agitated at 500 rpm. However, the specific L-asparaginase activity was not affected significantly by the rate of oxygen transfer. In most instances the level of dissolved oxygen decreased to zero before harvesting. KLa rather than dissolved oxygen as measured during the fermentation cycle is a more satisfactory index to determine the oxygen requirement for cell growth and asparaginase production. The optimum level of KLa for L-asparaginase production was 0.98 min−1. However, a higher value of KLa of 1.2–1.9 min−1 was needed to achieve the highest growth.