Feed Glucose Concentration Research Articles

Effect of Substrate Concentration (Glucose) on Ethanol Fermentation Continue with Immobilized Fixed Bed Fermenter for 2/3 Mesh Pumice Anchoring Size

The need for ethanol which is increasing at all times demands development related to ethanol production, especially those produced through the fermentation process both development in terms of raw materials and processes. Ethanol fermentation process continues to have problems one of them is wash out or the carrying of microorganisms into the product stream which causes the number of microorganisms to continue to decrease in the fermenter. One way to solve the problem of wash out is to tether the microorganism first to the anchoring medium (immobilized cell) and choose the suitable type of fermenter. The purpose of this study was to determine the effect of glucose concentration and the best conditions on the ethanol fermentation process continue with immobilized cell fixed bed fermenter to the value of ethanol concentration and yield ethanol produced as well as the percent of microorganisms still carried into the product streams. Based on the results of the study, the best conditions were obtained with a residence time of 2 days with the ethanol concentration of 1.20%v/v, the yield of fermented ethanol was 37.75%w/w, and % number of cells released was 0.45% at a glucose feed concentration of 150g/L. Fermentation is carried out under conditions of immobilized cell using microorganisms from the type of yeast Saccharomyces cerevisiae. In this study the variables that were considered fixed were the expansion ½ height of 1.47m column height, temperature of 25-30°C, and a pH of 5.5.

Bioprocess Optimisation for High Cell Density Endoinulinase Production from Recombinant Aspergillus niger.

Endoinulinase gene was expressed in recombinant Aspergillus niger for selective and high-level expression using an exponential fed-batch fermentation. The effects of the growth rate (μ), glucose feed concentration, nitrogen concentration and fungal morphology on enzyme production were evaluated. A recombinant endoinulinase with a molecular weight of 66 kDa was secreted. Endoinulinase production was growth associated at μ> 0.04 h-1, which is characteristic of the constitutive gpd promoter used for the enzyme production. The highest volumetric activity (670 U/ml) was achieved at a growth rate of 93% of μmax (0.07 h-1), while enzyme activity (506 U/ml) and biomass substrate yield (0.043 gbiomassDW/gglucose) significantly decreased at low μ (0.04 h-1). Increasing the feed concentration resulted in high biomass concentrations and viscosity, which necessitated high agitation to enhance the mixing efficiency and oxygen. However, the high agitation and low DO levels (ca. 8% of saturation) led to pellet disruption and growth in dispersed morphology. Enzyme production profiles, product (Yp/s) and biomass (Yx/s) yield coefficients were not affected by feed concentration and morphological change. The gradual increase in the concentration of nitrogen sources showed that, a nitrogen limited culture was not suitable for endoinulinase production in recombinant A. niger. Moreover, the increase in enzyme volumetric activity was still directly related to an increase in biomass concentration. An increase in nitrogen concentration, from 3.8 to 12 g/L, resulted in volumetric activity increase from 393 to 670 U/ml, but the Yp/s (10053 U/gglucose) and Yx/s (0.049 gbiomasDWs/gglucose) did not significantly change. The data demonstrated the potential of recombinant A. niger and high cell density fermentation for the development of large-scale endoinulinase production system.

Stability and Performance Analysis of Bioethanol Production with Delay and Growth Inhibition in a Continuous Bioreactor with Recycle

This paper proposes and analyzes a mathematical model for the production of bioethanol in a continuous bioreactor with recycling. The kinetics correspond to the use of Saccharomyces bayanus for the fermentation of sugars found in wastewater from soft drinks. The proposed model considers product growth latency, which was experimentally found in batch studies of ethanol production. Furthermore, the inhibition effect of ethanol is expressed by a modified version of the classical Andrew’s model for substrate inhibition. The proposed model consists of only three ordinary differential equations containing a minimal number of operating parameters, which include the bioreactor residence time, glucose feed concentration, recycle ratio and the fraction of biomass removed from the reactor by the flow. The positivity and the boundedness of solutions of the model were confirmed under reasonable restrictions of parameters. The stability analysis showed that there is a value of residence time at which an exchange of stability occurs between the trivial washout and non-washout solutions. This critical value depends only on the substrate feed concentration, biomass death rate, recycle ratio and purge fraction. Dynamic simulations of the model were carried out for substrate concentration in the range of 100–250 g/L, commonly used for the production of ethanol. An inverse response due to the inhibition effects of ethanol was observed in the time evolution of substrate and biomass concentrations. Parametric studies showed that ethanol concentration increases with the recycle ratio, with the inverse of residence time and with the inverse of purge fraction. The effect of ethanol latency has, on the other hand, a substantial effect on ethanol concentration. Despite its unstructured nature and the fact that some parameters such as temperature and acidity were not taken into consideration, the proposed model managed to provide useful results on the bioreactor-settler stability and the effect of key parameters on its dynamic behavior, which could pave the way for future optimization studies.

Differential Evolution Algorithm Based Self-adaptive Control Strategy for Fed-batch Cultivation of Yeast

In the fed-batch cultivation of Saccharomyces cerevisiae, excessive glucose addition leads to increased ethanol accumulation, which will reduce the efficiency of glucose utilization and inhibit product synthesis. Insufficient glucose addition limits cell growth. To properly regulate glucose feed, a different evolution algorithm based on self-adaptive control strategy was proposed, consisting of three modules (PID, system identification and parameter optimization). Performance of the proposed and conventional PID controllers was validated and compared in simulated and experimental cultivations. In the simulation, cultivation with the self-adaptive control strategy had a more stable glucose feed rate and concentration, more stable ethanol concentration around the set-point (1.0 g•L-1), and final biomass concentration of 34.5 g-DCW•L-1, 29.2% higher than that with a conventional PID control strategy. In the experiment, the cultivation with the self-adaptive control strategy also had more stable glucose and ethanol concentrations, as well as a final biomass concentration that was 37.4% higher than that using the conventional strategy.

Critical Quality Predictive Control of Fed-Batch Mammalian Cell Bioreactors

Abstract A model predictive control (MPC) formulation for a mammalian cell fed-batch bioreactor processes is developed. A nonlinear fundamental model for the bioreactor is used to generate a database of historical runs comprising of the measurement variables and the manipulated input feed flow rate to the bioreactor. The database is used with subspace identification methods to develop a state-space model of the process. The identified model is used to design various MPC formulations with different objective criteria, including the conventional trajectory-tracking objective function and a novel terminal objective for maximizing the product yield at completion of a run. Case studies involving the simulated bioreactor process demonstrate the efficacy of the MPC algorithms subject to unknown disturbances, random variations in the inlet feed glucose and glutamine concentrations, and measurement noise. Compared to the traditional proportional-integral control algorithm, the trajectory-tracking predictive control algorithm is able to better track the reference glucose concentration set-point with an improvement of 5.1% in the tracking error. The critical quality attribute predictive control algorithm designed to maximize the product yield results in a 3.9% increase in the product concentration at the completion of the run.

105 Chromium propionate improves insulin sensitivity in horses following oral concentrate consumption

Abstract Forty-eight Quarter Horse geldings (3–8 yr of age) were used to determine the effects of dietary chromium (Cr), in the form of Cr propionate (Cr Prop), on insulin sensitivity. Horses were blocked by age, body condition score, and glucose response to concentrate feeding on d 0, and randomly assigned to treatments. Treatments consisted of 0, 2, 4, or 8 mg Cr/d from Cr Prop. Horses were fed daily a concentrate mix at a rate of 0.2 kg/100 kg BW and grass hay at 1.75 to 2.0 kg/100 kg BW. After an overnight fast, jugular blood samples were obtained at 0, 2, and 4 h after concentrate feeding on d 0 and 28 for determination of glucose and insulin. Plasma glucose on d 28 was affected (P < 0.05) by treatment, time, and treatment x time. Horses fed 4 mg Cr/d had lesser (P < 0.05) plasma glucose concentrations than those in the other treatments at 0 h. At 2 h post feeding glucose concentrations were greater (P < 0.05) in control horses than in those given 4 mg Cr. Horses fed 2 mg Cr/d had lesser (P < 0.05) plasma glucose at 4 h post feeding compared to controls. Plasma glucose did not differ among horses receiving 2 or 4 mg Cr/d at 2 or 4 h. Insulin concentrations were greater (P < 0.05) in horses fed 0 or 2 mg Cr/d than in those given 4 or 8 mg Cr at 0 h. At 4 h post feeding insulin concentrations were greater (P < 0.05) in control horses than in those fed 2 or 4 mg Cr/d. Results of this study indicate that 2 or 4 mg Cr/d from Cr Prop increased insulin sensitivity in adult horses following oral carbohydrate consumption.

Novel dynamic membrane, metabolic flux balance and PICRUSt analysis for high-rate biohydrogen production at various substrate concentrations

This research aimed to implement high-rate biohydrogen production using dynamic membrane at various substrate concentrations. Two identical dynamic membrane bioreactors (DMBRs) on the laboratory scale were equipped with polyester mesh of 444-μm pore size. The DMBRs were continuously fed with glucose as a model substrate at 15, 20, and 25 g/L at hydraulic retention times (HRTs) of 2 h and 3 h. The DMBR enabled high-rate hydrogen production at both HRTs in long-term operation without backwashing. The peak average H2 production rate (HPR) and H2 yield (HY) per glucoseconsumed was 58.86 ± 0.73 L/L-d and 2.00 ± 0.04 mol H2/mol glucoseconsumed, respectively, with a feed glucose concentration of 20 g/L at 2 h HRT. At 3 h HRT, the highest HPR and HY were 29.81 ± 1.01 L/L-d and 1.53 ± 0.05 mol H2/mol glucoseconsumed with a feed glucose concentration of 20 g/L, respectively. HPR and HY were decreased in other feed concentration (15 g/L and 25 g/L) at each HRT, which was concomitant with metabolic flux shifted to lactic acid production and homoacetogenesis. Additionally, substrate consumption efficiency decreased at a feed concentration of 25 g/L. The microbial population at 20 g/L was dominated by Clostridium sp. and lactic acid bacteria. PICRUSt bioinformatics predicted the highest ferredoxin hydrogenase expression and LDH expression of Clostridium sp.

Enhancing thermophilic dark fermentative hydrogen production at high glucose concentrations via bioaugmentation with Thermotoga neapolitana

The aim of the present study was to investigate the effect of gradually increasing glucose concentrations (from 5.6 to 111 mmol L−1) on the fermentative H2 production with and without bioaugmentation. A stirred tank reactor (STR) was operated at 70 °C and inoculated with a hyperthermophilic mixed culture or a hyperthermophilic mixed culture bioaugmented with Thermotoga neapolitana. With both the unaugmented (control) and augmented cultures, the H2 production rate was improved when the initial glucose concentration was increased. In contrast, the highest H2 yield (1.68 mol H2 mol−1 glucose consumed) was obtained with the augmented culture at the lowest glucose concentration of 5.6 mmol L−1 and was 37.5% higher than that obtained with the unaugmented culture at the same feed glucose concentration. Overall, H2 production rates and yields were higher in the bioaugmented cultures than in the unaugmented cultures whatever the glucose concentration. Quantitative polymerase chain reaction targeting T. neapolitana hydA gene and MiSeq sequencing proved that Thermotoga was not only present in the augmented cultures but also the most abundant at the highest glucose concentrations.

Effects of toll-like receptor-7 agonists on feeding behaviour, voluntary activity, cloacal temperature and crop emptying in chicks

ABSTRACT 1. The purpose of the present study was to determine if an intraperitoneal injection of two toll-like receptor-7 (TLR7) agonists, imiquimod and resiquimod, affect feed intake, voluntary activity, cloacal temperature, crop-emptying rate, plasma corticosterone (CORT) and glucose concentrations, and splenic gene expression of cytokines in chicks (Gallus gallus). 2. Although intraperitoneal injection of 100 µg imiquimod significantly increased splenic gene expression of interleukin-1β (IL-1β), IL-6, IL-8, and interferon-γ (IFN-γ), it did not affect feed intake, voluntary activity, cloacal temperature, crop-emptying rate or plasma constituents. 3. Intraperitoneal injection of 100 µg resiquimod significantly decreased feed intake, voluntary activity, cloacal temperature, crop-emptying rate and increased plasma corticosterone concentrations. 4. Intraperitoneal injection of resiquimod significantly increased splenic gene expression of IL-1β, IL-6, IL-8, IFN-γ, and tumour necrosis factor-like cytokine 1A. 5. The results showed that activation of TLR7 is associated with anorexia, hypoactivity, hypothermia, disturbance of feed passage in the digestive tract and the response to stress in chicks.

Thermal Cracking of Sugars for the Production of Glycolaldehyde and Other Small Oxygenates.

Thermal cracking of sugars for production of glycolaldehyde, a potential renewable platform molecule, in yields up to 74 % with up to 95 % carbon recovered in the condensed product is demonstrated using glucose as the feed. The process involves spraying an aqueous sugar solution into a fluidized bed of glass beads. Continuous operation is carried out for more than 90 h with complete conversion and stable product selectivity. Besides glycolaldehyde, the other identified condensed products are pyruvaldehyde (9 %), formaldehyde (7 %), glyoxal (2 %), acetol (2 %), and acetic acid (1 %). The effects of temperature, glucose feed concentration, and type of sugar feedstock are investigated. Cracking the monosaccharides fructose and xylose leads to very different product distributions from glucose, but similar carbon recovery. A reaction network in agreement with the main observed products from cracking of monosaccharide sugars is proposed.

Enhancement of acetyl-CoA by acetate co-utilization in recombinant Lactococcus lactis cultures enables the production of high molecular weight hyaluronic acid.

The molecular weight of hyaluronic acid (HA) is a critical property which determines its usage in various biomedical applications. This study investigates the correlation between the availability of a critical cofactor, acetyl-CoA, the concentration of a limiting precursor, UDP-N-acetylglucosamine (UDP-GlcNAc), and the molecular weight of HA (MWHA) produced by recombinant Lactococcus lactis MKG6 cultures. This strain expressed three heterologous HA-pathway genes obtained from the has operon of Streptococcus zooepidemicus in an ldh-mutant host strain, L. lactis NZ9020. A flux balance analysis, performed using the L. lactis genome-scale metabolic network, showed a positive correlation of acetyl-CoA flux with the UDP-GlcNAc flux and the experimental data on HA productivity. To increase the intracellular levels of acetyl-CoA, acetate was supplemented as a pulse feed in anaerobic batch cultures. However, acetate is effectively utilized only in the presence of glucose and exhaustion of glucose resulted in decreasing the final MWHA (1.5 MDa). Co-supplementation of acetate resulted in enhancing the acetyl-CoA and UDP-GlcNAc levels as well as the MWHA to 2.5 MDa. This logic was extended to fed-batch cultures, designed with a pH-based feedback control of glucose feeding and pulse acetate supplementation. When the glucose feed concentration was optimally adjusted to prevent glucose exhaustion or accumulation, the acetate utilization was found to be high, resulting in significantly enhanced levels of acetyl-CoA and UDP-GlcNAc as well as a MWHA of 3.4 MDa, which was sustained at this value throughout the process. This study provides the possibility of commercially producing high MWHA using recombinant L. lactis strains.

Lectin bio‐layer interferometry for assessing product quality of Fc‐ glycosylated immunoglobulin G

Glycosylation, as the most prominent posttranslational modification, is recognized as an important quality attribute of monoclonal antibodies affected by various bioprocess parameters and cellular physiology. A method of lectin‐based bio‐layer interferometry (LBLI) to relatively rank galactosylation and fucosylation levels was developed. For this purpose, Fc‐glycosylated immunoglobulin G (IgG) was recombinantly produced with varying bioprocess conditions in 15 L bioreactor and accumulated IgG was harvested. The reliability, the robustness and the applicability of LBLI to different samples has been proven. Data obtained from LC–MS analysis served as reference and were compared to the LBLI results. The introduced method is based on non‐fluidic bio‐layer interferometry (BLI), which becomes recently a standard tool for determining biomolecular interactions in a label‐free, real‐time and high‐throughput manner. For the intended purpose, biotinylated lectins were immobilized on disposable optical fiber streptavidin (SA) biosensor tips. Aleuria aurantia lectin (AAL) was used to detect the core fucose and Ricinus communis agglutinin 120 (RCA120) to determine galactosylation levels. In our case study it could be shown that fucosylation was not affected by variations in glucose feed concentration and cultivation temperature. However, the galactosylation could be correlated with the ratio of mean specific productivity (qP) and ammonium (qNH4+) but was unrelated to the ratio of mean qP and the specific glucose consumption (qgluc). This presented method strengthens the applicability of the BLI platform, which already enables measurement of several product related characteristics, such as product quantity as well as kinetic rates (kd,kon) and affinity constants (kD) analysis.

Application of a multiphase microreactor chemostat for the determination of reaction kinetics of Staphylococcus carnosus.

Bioreactors at the microliter scale offer a promising approach to accelerate bioprocess development. Advantages of such microbioreactors include a reduction in the use of expensive reagents. In this study, a chemostat operation mode of a cuvette-based microbubble column bioreactor made of polystyrene (working volume of 550 µL) was demonstrated. Aeration occurs through a nozzle (Ø ≤ 100µm) and supports submerged whole-cell cultivation of Staphylococcus carnosus. Stationary concentrations of biomass and glucose were determined in the dilution rate regime ranging from 0.12 to 0.80 1/h with a glucose feed concentration of 1g/L. For the first time, reaction kinetics of S. carnosus were estimated from data obtained from continuous cultivation. The maximal specific growth rate (µmax = 0.824 1/h), Monod constant (KS = 34×10- 3gS/L), substrate-related biomass yield coefficient (YX/S = 0.315 gCDW/gS), and maintenance coefficient (mS = 0.0035 gS/(gCDW·h)) were determined. These parameters are now available for further studies in the field of synthetic biology.

Effect of feed glucose and acetic acid on continuous biohydrogen production by Thermotoga neapolitana

This study focused on the effect of feed glucose and acetic acid on biohydrogen production by Thermotoga neapolitana under continuous-flow conditions. Increasing the feed glucose concentration from 11.1 to 41.6 mM decreased the hydrogen yield from 3.6 (±0.1) to 1.4 (±0.1) mol H2/mol glucose. The hydrogen production rate concomitantly increased until 27.8 mM of feed glucose but remained unaffected when feed glucose was further raised to 41.6 mM. Increasing the acetic acid concentration from 0 to 240 mM hampered dark fermentation in batch bioassays, diminishing the cumulative hydrogen production by 45% and the hydrogen production rate by 57%, but induced no negative effect during continuous operation. Indeed, throughout the continuous flow operation the process performance improved considerably, as indicated by the 47% increase of hydrogen yield up to 3.1 (±0.1) mol H2/mol glucose on day 110 at 27.8 mM feed glucose.

Synthesis and techno-economic assessment of microbial-based processes for terpenes production

BackgroundRecent advances in metabolic engineering enable the production of chemicals from sugars through microbial bio-conversion. Terpenes have attracted substantial attention due to their relatively high prices and wide applications in different industries. To this end, we synthesize and assess processes for microbial production of terpenes.ResultsTo explain a counterintuitive experimental phenomenon where terpenes such as limonene (normal boiling point 176 °C) are often found to be 100% present in the vapor phase after bio-conversion (operating at only ~ 30 °C), we first analyze the vapor–liquid equilibrium for systems containing terpenes. Then, we propose alternative production configurations, which are further studied, using limonene as an example, in several case studies. Next, we perform economic assessment of the alternative processes and identify the major cost components. Finally, we extend the assessment to account for different process parameters, terpene products, ways to address terpene toxicity (microbial engineering vs. solvent use), and cellulosic biomass as a feedstock. We identify the key cost drivers to be (1) feed glucose concentration (wt%), (2) product yield (% of maximum theoretical yield) and (3) VVM (Volume of air per Volume of broth liquid per Minute, i.e., aeration rate in min−1). The production of limonene, based on current experimental data, is found to be economically infeasible (production cost ~ 465 $/kg vs. market selling price ~ 7 $/kg), but higher glucose concentration and yield can lower the cost. Among 12 terpenes studied, limonene appears to be the most reasonable short-term target because of its large market size (~ 160 million $/year in the US) and the relatively easier to achieve break-even yield (~ 30%, assuming a 14 wt% feed glucose concentration and 0.1 min−1 VVM).ConclusionsThe methods proposed in this work are applicable to a range of terpenes as well as other extracellular insoluble chemicals with density lower than that of water, such as fatty acids. The results provide guidance for future research in metabolic engineering toward terpenes production in terms of setting targets for key design parameters.

Quantifying the parametric sensitivity of ethanol production by Scheffersomyces (Pichia) stipitis: development and verification of a method based on the principles of growth on mixtures of complementary substrates.

Under aerobic conditions, Crabtree-negative yeasts grow but do not ferment, and under anaerobic conditions, they ferment but do not grow. It is therefore believed that fermentation by these yeasts is sensitive to small variations of the operating parameters, e.g. dilution rate D, mass transfer coefficient kla and oxygen solubility co*. However, this parametric sensitivity has never been quantified. Here, we present a method to quantify the parametric sensitivity of ethanol production in the Crabtree-negative yeast Scheffersomycesstipitis. The method is based on our experimental observation that S. stipitis cultures follow the principles of growth on mixtures of complementary substrates. Specifically, if a chemostat operating at fixed D, kla and co* is fed with progressively increasing glucose feed concentrations sf, the culture passes through three regimes. (1) At low sf, the culture is carbon-limited and no ethanol is produced. (2) At high sf, the culture is oxygen-limited and ethanol is produced, but unused glucose is lost with the effluent. (3) At intermediate sf, both glucose and oxygen are limiting, and ethanol is produced without loss of glucose. Ethanol must therefore be produced in this dual-limited regime. The dual-limited regime can be predicted by simple unstructured models. It is characterized by the relation Yos<Dsf/kla⋅co∗<Yos', where Yos and Yos' denote the g of glucose consumed per g of oxygen during carbon- and oxygen-limited growth. Hence, the parametric sensitivity of fermentation by Crabtree-negative yeasts can be improved by targeting the yields Yos and Yos'.

High glucose and low specific cell growth but not mild hypothermia improve specific r-protein productivity in chemostat culture of CHO cells.

In the biopharmaceutical sector, Chinese hamster ovary (CHO) cells have become the host of choice to produce recombinant proteins (r-proteins) due to their capacity for correct protein folding, assembly, and posttranslational modification. However, the production of therapeutic r-proteins in CHO cells is expensive and presents insufficient production yields for certain proteins. Effective culture strategies to increase productivity (qp) include a high glucose concentration in the medium and mild hypothermia (28–34 °C), but these changes lead to a reduced specific growth rate. To study the individual and combined impacts of glucose concentration, specific growth rate and mild hypothermia on culture performance and cell metabolism, we analyzed chemostat cultures of recombinant human tissue plasminogen activator (rh-tPA)-producing CHO cell lines fed with three glucose concentrations in feeding media (20, 30 and 40 mM), at two dilution rates (0.01 and 0.018 1/h) and two temperatures (33 and 37 °C). The results indicated significant changes in cell growth, cell cycle distribution, metabolism, and rh-tPA productivity in response to the varying environmental culture conditions. High glucose feed led to constrained cell growth, increased specific rh-tPA productivity and a higher number of cells in the G2/M phase. Low specific growth rate and temperature (33 °C) reduced glucose consumption and lactate production rates. Our findings indicated that a reduced specific growth rate coupled with high feed glucose significantly improves r-protein productivity in CHO cells. We also observed that low temperature significantly reduced qp, but not cell growth when dilution rate was manipulated, regardless of the glucose concentration or dilution rate. In contrast, we determined that feed glucose concentration and consumption rate were the dominant aspects of the growth and productivity in CHO cells by using multivariate analysis.

Biohydrogen production integrated with an external dynamic membrane: A novel approach

A dynamic membrane bioreactor integrating a self-forming dynamic membrane with a continuous fermenter was designed for biohydrogen production using mixed cultures under mesophilic conditions. The novel configuration used was designed to retain effective hydrogen producing bacterial consortia and was investigated at hydraulic retention times (HRTs) of 12–2 h at a constant glucose feed concentration of 15 g/L. A dynamic membrane was successfully formed on support material in an external module and this resulted in a maximum hydrogen production rate of 51.38 L/L-day and a peak hydrogen yield of 2.98 mol/mol glucoseadded at 3 h HRT. Acetate and butyrate were dominant metabolic by-products. Quantitative polymerase chain reaction (qPCR) analysis revealed that Clostridium butyricum was the dominant microbial consortium under all HRT conditions examined.

Relationships among Feed Intake, Blood Metabolites, Follicle Size and Progesterone Concentration in Ewes Exhibiting or Not Exhibiting Estrus after Estrous Synchronization in the Tropics

Abstract The aim of this study was to determine the relationships among feed intake, blood metabolites, follicle size, and progesterone (P 4 ) concentration in ewes that did or did not exhibit estrus after estrous synchronization. Sixteen cycling, Merino ewes were synchronized for 12 days with a controlled internal drug release (CIDR) devices (300 mg P 4 ). Ewes were classified by estrous behavior as exhibited estrus (n=12) or did not exhibit estrus (n=4). Blood samples were collected at 0, 24, 48, and 72 h after CIDR removal to measure glucose, blood urea nitrogen (BUN), and P 4 concentrations. Follicular size was examined by transrectal ultrasonography on the day of CIDR removal. Ewes exhibiting estrus had greater concentrations of glucose at 24 and 48 h after CIDR withdrawal than ewes that did not exhibit estrus. Ewes exhibiting estrus had decreased concentrations of P 4 at 24 and 48 h after CIDR withdrawal compared with ewes that did not exhibit estrus. At the time of CIDR withdrawal, the diameter of largest follicle was observed greater in ewes exhibiting estrus than that in ewes not exhibiting estrus. By 48 h after CIDR removal, 91.7% of ewes that displayed estrous behavior had exhibited estrus. In all ewes, a significant positive relationship was observed between feed intake and glucose concentration. Follicle diameter was positively correlated with glucose and P 4 concentrations but was negatively correlated with time to onset of estrus in ewes exhibiting estrus. No relationship was detected between BUN and other parameters in all ewes. In conclusion, increased estrous activity in ewes synchronized to estrus may result from increased size of follicle, low P 4 levels, and sufficient production of glucose during the follicular development. Thus, these data highlight the importance of follicle diameter, glucose concentration, and time to onset of estrus in ewes exhibiting estrus under tropical conditions.

Experimental and in silico investigation of population heterogeneity in continuous Sachharomyces cerevisiae scale‐down fermentation in a two‐compartment setup

AbstractBACKGROUNDIn large‐scale bioreactors, microbes often encounter fluctuating conditions of nutrient and oxygen supply, resulting in different microbial behavior at the different scales. The underlying reason is spatial heterogeneity, caused by limited mixing capabilities at production scale. Consequently, scale‐up of processes is challenging and there is a need for laboratory‐scale reactor setups that can mimic large‐scale conditions to enhance the understanding of how fluctuating environmental conditions affect microbial physiology.RESULTSA two‐compartment, scale‐down setup, consisting of two interconnected stirred tank reactors was used in combination with mathematical modeling, to mimic large‐scale continuous cultivations. One reactor represents the feeding zone with high glucose concentration and low oxygen, whereas the other one represents the remaining reactor volume. An earlier developed population balance model coupled to an unstructured model was used to describe the development of bulk concentrations and cell size distributions at varying dilution rate, glucose feed concentration as well as recirculation times between the two compartments. The concentration profiles of biomass and glucose were successfully validated experimentally. Single cell properties of two fluorescent reporter strains that were applied for deeper investigation of cell robustness characteristics and ethanol growth distributions were quantified compartment‐wise revealing differences in cell population distributions related to environmental conditions and also compared with the one‐compartment, conventional chemostat.CONCLUSIONResults underline the utility for the proposed combined approach as well as the use of continuous scale‐down reactors for process investigations as insights concerning single‐cell characteristics of the process are revealed, which are normally hidden. © 2014 Society of Chemical Industry