Oxygen Transfer Conditions Research Articles

β-Sitosterol Bioconversion in Small-Scale Devices: From Microtiter Plates to Microfluidic Reactors.

Small-scale devices are routinely used as low-cost miniaturized bioreactors due to the large number of experiments that can be conducted simultaneously under similar conditions and replicate all functions of bench-scale reactors at dramatically smaller volumes. Microtiter plates, due to the standard footprint, can be integrated with liquid handling systems and associated equipment, expanding considerably their application and use. However, care has to be taken to operate the microtiter plates in optimized mixing and oxygen transfer conditions, preventing medium evaporation in prolonged experiment runs. Recently, to increase data quality, microbioreactors have emerged as an alternative to shaken systems. These systems offer higher degree of control over key process variables and when combined with sensing technology increase dramatically the reliability of translational process data. In this chapter, we describe the production of 4-androstene-3,17-dione (androstenedione (AD)), a key pharmaceutical steroid intermediate, by Mycobacterium sp. NRRL B-3805 via the selective cleavage of the side-chain of β-sitosterol using 24-well microtiter plates and microfluidic microbioreactors.

Production of alginates with high viscosifying power and molecular weight by using the AT9 strain of Azotobacter vinelandii in batch cultures under different oxygen transfer conditions

AbstractBackgroundAlginate is a polysaccharide constituted by β‐d‐mannuronic acid and α‐l‐guluronic which has several applications in the field of tissue engineering, drug delivery and other biomedical applications. This study aimed to evaluate the production, molecular weight (MW) and viscosifying power of the alginate produced by the strain AT9 cultured in a 3‐L reactor, under three different oxygen transfer rates (OTR).ResultsAn increase in the OTRmax, in the range of 3.6–12.4 mmol L−1 h−1 promoted cellular growth and alginate production in the cultures, reaching a specific growth rate of 0.14 h−1 and a maximal alginate concentration of 2.9 g L−1 in cultures developed at 12.4 mmol L−1 h−1. By contrast, at low OTR (3.6 mmol L−1 h−1) a maximal molecular weight of 2927 kDa was obtained and at high OTRmax (12.4 mmol L−1 h−1) the maximal acetylation degree (2–3%) was reached. As a result of the higher acetylation of the alginate, the viscosifying power was the highest (3.16 L g−1).ConclusionOverall, our results indicate that by controlling the OTRmax it is possible to manipulate the MW, the acetylation degree and the viscosifying power of bacterial alginates produced by strain AT9. © 2022 The Authors. Journal of Chemical Technology and Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry (SCI).

Optimization of Aeration and Agitation for α-amylase production by Aspergillus flavus from water hyacinth

Amylases are a group of commercially important enzymes with various clinical, medical and biotechnological applications. The current study aims to optimize the agitation and aeration (oxygen transfer) conditions for α-amylase production by Aspergillus flavus using water hyacinth extract; as an available waste and very cheap nutritional substance, in a lab scale stirred tank bioreactor (submerged fermentation). Data showed that the maximal cell biomass and enzyme specific activity were reached at low aeration rate (0.5 v/v/m) and moderate agitation speed (200 rpm). The maximum specific amylase production rate has been reached after 24 hrs. In addition, it has been confirmed that scaling-up Aspergillus flavus does not, inversely, affect α-amylase productivity compared with flask level production. Aspergillus flavus has been approved as promising fungal isolate for production of a-amylase using water hyacinth for application in many fields.

ALBA: A comprehensive growth model to optimize algae-bacteria wastewater treatment in raceway ponds

This paper proposes a new model describing the algae-bacteria ecosystem evolution in an outdoor raceway for wastewater treatment. The ALBA model is based on mass balances of COD, C, N and P, but also H and O. It describes growth and interactions among algae, heterotrophic and nitrifying bacteria, while local climate drives light and temperature. Relevant chemical/physical processes are also included. The minimum-law was used as ground principle to describe the multi-limitation kinetics. The model was set-up and calibrated with an original data set recorded on a 56 m2 raceway located in the South of France, continuously treating synthetic wastewater. The main process variables were daily measured along 443 days of operations and dissolved O2 and pH were on-line recorded. A sub-dataset was used for calibration and the model was successfully validated, along the different seasons over a period of 414 days. The model proved to be effective in reproducing both the short term nycthemeral dynamics and the long-term seasonal ones. The analysis of different scenarios reveals the fate of nitrogen and the key role played by oxygen and CO2 in the interactions between the different players of the ecosystem. On average, the process turns out to be CO2 neutral, as compared to a standard activated sludge where approximately half of the influent carbon will end up in the atmosphere. The ALBA model revealed that a suboptimal regulation of the paddle wheel can bring to several detrimental impacts. At high velocity, the strong aeration will reduce the available oxygen provided by photo-oxygenation, while very low aeration can rapidly lead to oxygen inhibition of the photosynthetic process. On the other hand, during night, the paddle wheel is fundamental to ensure enough oxygen in the system to support algal-bacteria respiration. The model can be used to support advanced control strategies, including smart regulation of the paddle wheel velocity to more efficiently balance the mixing, aeration and degassing effects.

Production of Poly-3-Hydroxybutyrate (P3HB) with Ultra-High Molecular Weight (UHMW) by Mutant Strains of Azotobacter vinelandii Under Microaerophilic Conditions.

Poly-3-hydroxybutyrate (P3HB) is a biopolymer, which presents characteristics similar to those of plastics derived from the petrochemical industry. The thermomechanical properties and biodegradability of P3HB are influenced by its molecular weight (MW). The aim of the present study was to evaluate the changes of the molecular weight of P3HB as a function of oxygen transfer rate (OTR) in the cultures using two strains of Azotobacter vinelandii, a wild-type strain OP, and PhbZ1 mutant with a P3HB depolymerase inactivated. Both strains were grown in a bioreactor under different OTR conditions. An inverse relationship was found between the average molecular weight of P3HB and the OTRmax, obtaining a polymer with a maximal MW (8000-10,000kDa) from the cultures developed at OTRmax of 5mmolL-1h-1 using both strains, with respect to the cultures conducted at 8 and 11mmolL-1h-1, which produced a P3HB between 4000 and 5000kDa. The increase in MW of P3HB was related to the activity of enzymes involved in the synthesis and depolymerization. Overall, our results show that it is possible to modulate the average molecular weight of P3HB by manipulating oxygen transfer conditions with both strains (OP and PhbZ1 mutant) of A. vinelandii.

Productivity and scale‐up of poly(3‐hydroxybutyrate) production under different oxygen transfer conditions in cultures of Azotobacter vinelandii

AbstractBackgroundPoly(3‐hydroxybutyrate) (PHB) is a polymer produced by Azotobacter vinelandii. The production of PHB in a bioreactor is affected by oxygen transfer conditions. The aim of this study was to evaluate PHB synthesis in extended batch of A. vinelandii, to obtain an operation curve (productivity versus oxygen transfer rate) and to scale up the bioprocess.ResultsPHB production by A. vinelandii under dinitrogen fixation was evaluated using an extended batch modality under different oxygen transfer rates (OTRs). Extended batch cultures were performed using different agitation rates (400, 600, 800 and 1000 rpm), which determined different OTRs in the cultures. Under the conditions evaluated, it was possible to establish an operation curve of PHB productivity at different OTRs, allowing for the establishment of the maximum productivity of PHB. The maximum PHB productivity obtained was 0.40 ± 0.05 g L−1 h−1, which was reached under an OTR of 22.1 ± 1.5 mmol L−1 h−1. Using the OTR as a criterion to scale up PHB production from 3 to 30 L, it was possible to obtain a similar PHB concentration (7.9 ± 0.0 g L−1) and volumetric productivity (0.43 ± 0.04 g L−1 h−1) on a 30 L scale.ConclusionsThe results lead to the conclusion that in extended cultures and under dinitrogen fixation in A. vinelandii cultures, the OTR value determines the maximum PHB productivity. This study provides evidence that the OTR is an adequate parameter as a criterion for the successful scaling up of PHB synthesis for the first time. © 2020 Society of Chemical Industry

Process optimization involving critical evaluation of oxygen transfer, oxygen uptake and nitrogen limitation for enhanced biomass and lipid production by oleaginous yeast for biofuel application.

Lipid accumulation in oleaginous yeast is generally induced by nitrogen starvation, while oxygen saturation can influence biomass growth. Systematic shake flask studies that help in identifying the right nitrogen source and relate its uptake kinetics to lipid biosynthesis under varying oxygen saturation conditions are very essential for addressing the bioprocessing-related issues, which are envisaged to occur in the fermenter scale production. In the present study, lipid bioaccumulation by P. guilliermondii at varying C:N ratios and oxygen transfer conditions (assessed in terms of kLa) was investigated in shake flasks using a pre-optimized N-source and a two-stage inoculum formulated in a hybrid medium. A maximum lipid concentration of 10.8 ± 0.5gL-1 was obtained in shake flask study at the optimal condition with an initial C:N and kLa of 60:1 and 0.6min-1, respectively, at a biomass specific growth rate of 0.11h-1. Translating these optimal shake flask conditions to a 3.7L stirred tank reactor resulted in biomass and lipid concentrations of 16.74 ± 0.8 and 8 ± 0.4gL-1. The fatty acid methyl ester (FAME) profile of lipids obtained by gas chromatography was found to be suitable for biodiesel application. We strongly believe that the rationalistic approach-based design of experiments adopted in the study would help in achieving high cell density with improved lipid accumulation and also minimize the efforts towards process optimization during bioreactor level operations, consequently reducing the research and development-associated costs.

Analyses of extracellular protein production in Bacillus subtilis – I: Genome-scale metabolic model reconstruction based on updated gene-enzyme-reaction data

Bacillus subtilis genome-scale model (GEM) reconstruction was stimulated by the recent sequencing and consequent re-annotations. The updated gene-enzyme-reaction data were collected from databases to reconstruct B. subtilis reaction network BsRN-2016 containing 1144 genes linked to 1955 reactions and 1103 metabolites. Thermodynamic analysis was conducted to identify reversibility and directionality of the reactions. By elimination of unconnected-reactions from BsRN-2016, reconstruction process of the first third-generation GEM iBsu1144 employing 1083 reactions linked to 719 genes was completed. The stoichiometric flux-balance based model was solved using time-profiles of serine alkaline protease fermentation-data at three different oxygen-transfer conditions creating perturbations on the intracellular reaction-network. Testing iBsu1144 dignity with three different objective functions indicated superior robustness of the GEM. Comparison of iBsu1144 results with a second-generation GEM was demonstrated. Insights obtained from flux distributions were used to determine metabolic engineering sites. Asparagine, isoleucine, threonine, and aspartic acid were determined as the primary rate-limiting amino acids to be considered as corresponding metabolic engineering sites in SAP synthesis in B. subtilis. Flux variability analysis carried out for the optimum condition reveals that 288 reactions are active and linked to 317 genes, so called substantial genes. The blocked 735 reactions linked to 533 genes, formed a platform for guided gene deletions in B. subtilis to generate simplified host strains.

Analyses of extracellular protein production in Bacillus subtilis – II: Responses of reaction network to oxygen transfer at transcriptional level

Oxygen transfer influences intracellular fluxes which are orchestrated by genome and its transcription in Bacillus subtilis throughout fermentation in recombinant human growth hormone (rhGH) production. Responses of B. subtilis reaction network to oxygen transfer were analysed at transcriptional level with determined transcriptome and calculated intracellular fluxes by the reconstructed genome scale model iBsu1144rhGH based on updated gene-enzyme-reaction data. iBsu1144rhGH employing 1067 reactions linked to 719 genes was solved using time-profiles of rhGH fermentation data at three oxygen transfer conditions from low- to high- to create perturbations on the intracellular reaction-network. Insights obtained from transcriptional and metabolic responses were used to determine metabolic engineering sites. Flux variability analyses results reveal that 305 reactions are active, linked to 346 genes so called substantial genes; and, 730 reactions linked to 536 genes blocked in rhGH synthesis were determined with their enzymes, genes, and reaction fluxes to create a platform for guided gene deletions. Effects of oxygen transfer on the transcriptome of r-B. subtilis carrying hGH gene were investigated further with one-way analysis of variance with the confidence greater than 99.5% and the expression ratios greater than 3. Fifty probe sets were found to be significantly affected from oxygen transfer where eight genes performed different transcriptional and metabolic responses to oxygen transfer and determined as metabolic engineering sites besides scoC and degU.

β-Sitosterol Bioconversion to Androstenedione in Microtiter Plates.

Microtiter plates are routinely used as low-cost miniaturized bioreactors due to the large number of experiments that can be conducted simultaneously under similar conditions and replicate all functions of bench-scale reactors at dramatically smaller volumes. These plates, due to the standard footprint, can be integrated with liquid-handling systems and associated equipment expanding considerably their application and use. However, care has to be taken to operate the microtiter plates in optimized mixing and oxygen transfer conditions, preventing medium evaporation in prolonged experiment runs. Here, we describe the production of 4-androstene-3,17-dione (androstenedione; AD), a key pharmaceutical steroid intermediate, by Mycobacterium sp. NRRL B-3805 via the selective cleavage of the side-chain of β-sitosterol using 24-well microtiter plates.

A new method to measure oxygenator oxygen transfer performance during cardiopulmonary bypass: clinical testing using the Medtronic Fusion oxygenator.

There is no acceptable method of testing oxygen transfer performance in membrane oxygenators quickly and easily during cardiopulmonary bypass. Pre-clinical testing of oxygenators is performed under controlled situations in the laboratory, correlating oxygen transfer to blood flow using 100% oxygen. This laboratory method cannot be used clinically as oxygen transfer values vary significantly at each blood flow and the FiO2 is not kept at 1. Therefore, a formula was developed which corrects the existing FiO2 to attain a PaO2 of 150 mmHg: the corrected FiO2 at 150 mmHg. In graph form, this corrected FiO2 (x-axis) is correlated to the patient's oxygen consumption levels (y-axis), which determines the membrane oxygenator oxygen transfer performance. Blood gas and hemodynamic parameters taken during cardiopulmonary bypass using the Medtronic Fusion were used to calculate the oxygen consumption (inlet conditions to the oxygenator) and the corrected FiO2 for a PaO2 of 150 mmHg. Validation of the formula "FiO2-PaO2/(Pb-pH2O)+0.21" was carried out by plotting the calculated values on a graph using PaO2 values between 145 to 155 mmHg and then, using the corrected FiO2 for PaO2s outside of this range. All trend-lines correlated significantly to confirm that the Medtronic Fusion had an extrapolated oxygen transfer of 419 milliliters O2/min at an FiO2 of 1 to achieve a PaO2 of 150 mmHg. Use of the corrected FiO2 correlated to the oxygen transfer conditions of the membrane oxygenator can easily be used on a routine basis, providing valuable information clinically. When used by the manufacturer under laboratory conditions, further clinically relevant data is provided in terms of FiO2 and resultant PaO2s instead of the present limitations using blood flow. In this way, a clinically justifiable method has been developed to finally establish a standard in testing membrane oxygenator performance.

Influence of oxygen transfer on Pseudomonas putida effects on growth rate and biodesulfurization capacity.

The growth rate and desulfurization capacity accumulated by the cells during the growth of Pseudomonas putida KTH2 under different oxygen transfer conditions in a stirred and sparged tank bioreactor have been studied. Hydrodynamic conditions were changed using different agitation conditions. During the culture, several magnitudes associated to growth, such as the specific growth rate, the dissolved oxygen concentration and the carbon source consumption have been measured. Experimental results indicate that cultures are influenced by the fluid dynamic conditions into the bioreactor. An increase in the stirrer speed from 400 to 700 rpm has a positive influence on the cell growth rate. Nevertheless, the increase of agitation from 700 to 2000 rpm hardly has any influence on the growth rate. The effect of fluid dynamics on the cells development of the biodesulfurization (BDS) capacity of the cells during growth is different. The activities of the intracellular enzymes involved in the 4S pathway change with dissolved oxygen concentration. The enzyme activities have been evaluated in cells at several growth time and different hydrodynamic conditions. An increase of the agitation from 100 to 300 rpm has a positive influence on the development of the overall BDS capacity of the cells during growth. This capacity shows a decrease for higher stirrer speeds and the activity of the enzymes monooxygenases DszC and DszA decreases dramatically. The highest value of the activity of DszB enzyme was obtained with cells cultured at 100 rpm, while this activity decreases when the stirrer speed was increased higher than this value.

Influence of oxygen on lovastatin biosynthesis by Aspergillus terreus ATCC 20542 quantitatively studied on the level of individual pellets.

Despite oxygen is believed to be the most important environmental factor for any aerobic microbial process, the quantitative studies of its influence on growth and metabolite formation on the level of individual pellets formed by filamentous fungi were seldom performed. Never was it made for lovastatin producer Aspergillus terreus ATCC20542. Thus, this work is a quantitative study of oxygen transfer into A. terreus pellets during lovastatin biosynthesis in the shake flask culture. The basic measurement tool was an oxygen microprobe allowing for obtaining oxygen concentration profiles in the pellets. The pellets of various sizes from 1,600 to 6,400 μm exerting different oxygen transfer conditions were studied. Also various initial concentrations of carbon source were applied to change the conditions of biological reaction running in the pellets. Effective diffusivities in A. terreus pellets ranged from 643 to 1,342 μm s−1 dependent on their size and structure. It occurred that only the smallest pellets of diameter equal to about 1,400 μm were fully penetrated by oxygen. What is more, apart from the size of pellets, the appropriate lactose concentration was required to effectively produce lovastatin. Its value was correlated with oxygen concentration on the surface of the pellet and could not be either too high, as the aforementioned oxygen level tended then to zero, or too low, as despite high oxygen concentration no biological reaction ran in the pellet and no lovastatin was formed.

Rapid assessment of oxygen transfer impact for Corynebacterium glutamicum.

Oxygen supply is crucial in industrial application of microbial systems, such as Corynebacterium glutamicum, but oxygen transfer is often neglected in early strain characterizations, typically done under aerobic conditions. In this work, a new procedure for oxygen transfer screening is presented, assessing the impact of maximum oxygen transfer conditions (OTRmax) within microtiter plate-based cultivation for enhanced throughput. Oxygen-dependent growth and productivity were characterized for C. glutamicum ATCC13032 and C. glutamicum DM1933 (lysine producer). Biomass and lysine product yield are affected at OTRmax below 14mmolL(-1)h(-1) in a standardized batch process, but not by further increase of OTRmax above this threshold value indicating a reasonable tradeoff between power input and oxygen transfer capacity OTRmax. The described oxygen transfer screening allows comparative determination of metabolic robustness against oxygen transfer limitation and serves identification of potential problems or opportunities later created during scale-up.

Oxygen transfer coefficient and the kinetic parameters of exo-polygalacturonase production by Aspergillus flavipes FP-500 in shake flasks and bioreactor.

To evaluate and compare the sensitivity of Exo-PG production and kinetic parameters of Aspergillus flavipes FP-500 to oxygen transfer condition in shake flasks and bioreactor. Aspergillus flavipes FP-500 was grown on pectin as carbon source in shake flasks and bioreactor at different oxygen transfer conditions. The volumetric coefficient of oxygen transfer (kLa) was modified by changing both, the flask size/medium volume ratio and the agitation speed. Higher biomass concentration, Exo-PG activity, maximum specific growth rate and yield coefficient were obtained in bioreactor at higher kLa value. A strong correlation was found between biomass, Exo-PG activity and growth-associated product coefficient to kLa in bioreactor but does not in shake flasks. The mathematical model provided a good description of growth, pectin consumption and Exo-PG production in submerged batch cultures carried out in bioreactor. Biomass concentration, Exo-PG activity and their kinetics of Aspergillus flavipes FP-500 were strongly influenced by oxygen transfer condition and cultivation system. Significance and Impact of Study The production of enzymes by fungal fermentation is strictly aerobic and understanding the influence of oxygen transfer condition on the production kinetic is of vital importance in order to design, optimize and translate bioprocesses to industrial scale.

Impact of energy supply and oxygen transfer on selective lipopeptide production by Bacillus subtilis BBG21

The influence of power dissipation and volumetric oxygen transfer coefficient kLa on Bacillus subtilis productivity of lipopeptides surfactin and fengycin was studied in shake flasks in view of scaling-up of this fermentation process. The experiments performed with different flask sizes, relative filling volumes, and shaking frequencies confirmed clearly that lipopeptide production changed in function of power dissipation, via interfacial gas–liquid contact surface and oxygen supply. It was demonstrated that kLa is the key parameter controlling the productivity and the selectivity of the bioreaction. Varying the oxygen transfer conditions, the synthesis could be oriented to mixed production or to surfactin mono-production. The fraction of surfactin towards total lipopeptides produced and the maximal surfactin production both increased with kLa increase (surfactin concentration about 2gL−1 at kLa=0.04–0.08s−1), while the maximal fengycin production (fengycin concentration about 0.3gL−1) was obtained at moderate oxygen supply (kLa=0.01s−1).

Shear conditions in clavulanic acid production by Streptomyces clavuligerus in stirred tank and airlift bioreactors

In biochemical processes involving filamentous microorganisms, the high shear rate may damage suspended cells leading to viability loss and cell disruption. In this work, the influence of the shear conditions in clavulanic acid (CA) production by Streptomyces clavuligerus was evaluated in a 4-dm(3) conventional stirred tank (STB) and in 6-dm(3) concentric-tube airlift (ALB) bioreactors. Batch cultivations were performed in a STB at 600 and 800 rpm and 0.5 vvm (cultivations B1 and B2) and in ALB at 3.0 and 4.1 vvm (cultivations A1 and A2) to define two initial oxygen transfer conditions in both bioreactors. The average shear rate ([Formula: see text]) of the cultivations was estimated using correlations of recent literature based on experimental data of rheological properties of the broth (consistency index, K, and flow index, n) and operating conditions, impeller speed (N) for STB and superficial gas velocity in the riser (UGR) for ALB. In the same oxygen transfer condition, the [Formula: see text] values for ALB were higher than those obtained in STB. The maximum [Formula: see text] presented a strong correlation with a maximum consistency index (K (max)) of the broth. Close values of maximum CA production were obtained in cultivations A1 and A2 (454 and 442 mg L(-1)) with similar maximum [Formula: see text] values of 4,247 and 4,225 s(-1). In cultivations B1 and B2, the maximum CA production of 269 and 402 mg L(-1) were reached with a maximum [Formula: see text] of 904 and 1,786 s(-1). The results show that high values of average shear rate increase the CA production regardless of the oxygen transfer condition and bioreactor model.

Fermentation medium and oxygen transfer conditions that maximize the xylose conversion to ethanol by Pichia stipitis

The xylose conversion to ethanol by Pichia stipitis was studied. In a first step, the necessity of supplementing the fermentation medium with urea, MgSO 4 × 7H 2O, and/or yeast extract was evaluated through a 2 3 full factorial design. The simultaneous addition of these three nutritional sources to the fermentation medium, in concentrations of 2.3, 1.0, and 3.0 g/l, respectively, showed to be important to improve the ethanol production in detriment of the substrate conversion to cell. In a second stage, fermentation assays performed in a bioreactor under different K La (volumetric oxygen transfer coefficient) conditions made possible understanding the influence of the oxygen transfer on yeast performance, as well as to define the most suitable range of values for an efficient ethanol production. The most promising region to perform this bioconversion process was found to be between 2.3 and 4.9 h −1, since it promoted the highest ethanol production results with practically exhaustion of the xylose from the medium. These findings contribute for the development of an economical and efficient technology for large scale production of second generation ethanol.

Mass production of the entomopathogenic nematode, Steinernema carpocapsae CABA01, through the submerged monoxenic culture in two internal-loop airlift bioreactors with some geometric differences

The submerged monoxenic culture of the entomopathogenic nematode, Steinernema carpocapsae CABA01, was carried out in two internal-loop airlift reactors (R1 and R2) with some geometric differences. Two runs each reactor were carried out at operating conditions V L = 4.22 L, Q = 1–1.5 vvm, T = 22 °C. The culture broth apparent viscosity changed from 2 to 12 mPa s determining global changes in both hydrodynamics (expressed as the dimensionless Reynolds number, Re) and oxygen transfer conditions (expressed as the k L a coefficient). Such changes were 170 < Re < 3080; 1.9 < k L a (10 −2 s −1) < 3.5 for R1 experiments, and 400 < Re < 10,060; 1.9 < k L a (10 −2 s −1) < 3.5, for R2 experiments. Infective juvenile stage (IJ) concentrations of 250,000/mL were achieved in R2 experiments whereas notably lower ones were obtained in R1 experiments (110,000 IJ/mL, approximately). The hydrodynamic conditions in both riser and downcomer sections of R2 experiments involved higher inertial forces than the corresponding ones to R1 runs, implying values of (Re R2/Re R1) riser from 2.3 to 3.3 and (Re R2/Re R1) downcomer from 1.8 to 2.5. These results suggest that higher inertial forces would promote the mating process among the vigorous adult nematodes of the first generation, probably due to encourage female–male encounters in response to a better mixing of the culture broth. Further, the nematode reproduction appeared to be greatly influenced by the reactor geometry.

Submerged monoxenic culture of the entomopathogenic nematode, Steinernema carpocapsae CABA01, in a mechanically agitated bioreactor: Evolution of the hydrodynamic and mass transfer conditions

This study is the first to describe the evolution of both hydrodynamic and oxygen transfer conditions during the submerged culture of the entomopathogenic nematode, Steinernema carpocapsae CABA01 (an indigenous strain isolated within the State of Hidalgo, Mexico), and its symbiotic bacterium, Xenorhabdus nematophila, using an internal-loop mechanically agitated bioreactor of 4.5 L of liquid volume. Concentrations up to 217,306 viable nematodes per mL, with 94% in infective juvenile (IJ) stage (i.e., 204,444 IJ/mL), were achieved in 16 days of bioprocess. The Reynolds number (Re) was used as an index of the actual hydrodynamic conditions, and it varied within the interval 5,150 < Re (dimensionless) < 9,440, involving apparent culture broth viscosity changes from 3 to 5.4 mPa s during the processing. The aeration efficiency was expressed on the basis of the volumetric oxygen transfer coefficient, kLa, which varied within the range 0.026 to 0.170 s−1.