Display omitted
•Shear conditions are important since they influence cell morphology and production.•Kinetic model using pellet fragmentation was proposed to quantify shear conditions.•β-Glucosidase ...and endoglucanase had linear dependence with the kinetic parameter.•β-Glucosidase production was higher under high shear conditions.•Endoglucanase production was favored under low shear conditions.
The hydrodynamic environment in bioreactors affects the oxygen transfer rate and the shear conditions during microbial cultivations. Therefore, assessment of the effect of the hydrodynamic environment on cellular morphology can contribute to favoring the production of metabolites of interest. The aim of this work was to use image analysis in order to quantify the fragmentation of Aspergillus niger pellets in a conventional bioreactor operated using different impeller speeds, air flow rates, and impeller configurations including Rushton turbines and Elephant Ear impellers, with evaluation of the influence of the hydrodynamic environment on the production of cellulolytic enzymes. An empirical kinetic model was proposed to describe the dynamics of pellet fragmentation and quantify the shear conditions. The results showed that the agitation speed affected the dynamics of pellet fragmentation in two ways, by accelerating the damage process and by increasing the magnitude of the fragmentation. Both endoglucanase and β-glucosidase production exhibited a linear relationship with the pellet fragmentation percentage, which was directly related to the shear conditions. Interestingly, β-glucosidase production was favored under high shear conditions, while the highest endoglucanase production occurred under low shear conditions. These findings may be useful for defining suitable systems and operating conditions for the production of metabolites including enzymes in bioreactors, as well as defining conditions that favour a specific pre-determined enzyme cocktail.
Display omitted
•Accumulation of endoglucanase or β-glucosidase is a function of mixing for A. niger.•The ratio of enzyme activities is indicative of mycelial morphology.•A form factor may be used to ...correlate the ratio of enzyme activities.•Dispersed forms of mycelia are responsible for β-glucosidase accumulation.
Endoglucanase and xylanase are critical enzymes for liquefaction and enzyme hydrolysis of high solids lignocellulosic biomass to facilitate its transport and production of desired derived products. Here is reported how combinations of different spore concentrations and pH influence microbial morphology, and how this may be used to direct expression and secretion of enzymes by Aspergillus niger. While xylanase production is not affected by A. niger morphology changes, endoglucanase production is enhanced under conditions of lower stress and by morphology that results in pellets. β-glucosidase production is enhanced under dispersed morphology, which results in up to fourfold increase of this enzyme production under the tested experimental conditions. A morphologic scale (Y) is proposed based on a form factor that considers the size and frequency of each morphology class, and that points to conditions that result in high selectivity for either endoglucanase or β-glucosidase production. An equation proposed to relate enzyme activity to morphology provides a useful tool for tuning enzyme production of A. niger, where morphology is a first indication of relative enzyme activities in a fermentation broth.
The manner in which added non‐catalytic proteins during enzymatic hydrolysis of lignocellulosic substrates enhances hydrolysis mechanisms is not completely understood. Prior research has indicated ...that a reduction in the non‐specific adsorption of enzymes on lignin, and deactivation of enzymes exposed to air–liquid interface provide rationale. This work investigated root causes including effects of the air–liquid interface on non‐catalytic proteins, and effects of lignin on endoglucanase. Three different experimental designs and three variables (air–liquid interfacial area, the types of lignin (acid or enzymatic lignin), and the presence of non‐enzymatic protein (bovine serum albumin BSA or soy proteins ) were used. The results showed that acid isolated lignin adsorbed almost all endoglucanase activity initially present in supernatant, independent of air interface conditions (25 or 250 ml flasks) with the presence of BSA preventing this effect. Endoglucanase lost 30%–50% of its activity due to an air–liquid interface in the presence of lignin while addition of non‐enzymatic protein helped to preserve this enzyme's activity. Langmuir and Freundlich models applied to experimental data indicated that the adsorption increases with increasing temperature for both endoglucanase and BSA. Adsorption of the enzyme and protein were endothermic with an increase in entropy. These results, combined, show that hydrophobicity plays a strong role in the adsorption of both endoglucanase and BSA on lignin.
•Gas stripping and vacuum were integrated into a fermentation process.•Factorial design was used to investigate the influence of operating conditions.•The gas stream was 6 times more concentrated in ...ethanol than the liquid phase.•The energy requirement for the vacuum-stripping process was reduced by 30.9%.
One way to overcome the inhibitory effects caused by ethanol on yeast cell growth is the use of extractive fermentation, whereby ethanol is removed from the fermentation broth as it is produced. The present work investigates ethanol removal from solution by vacuum-assisted gas stripping, which is a promising method for enhancing performance, compared to conventional gas stripping. Evaluation was made of the effects of carbon dioxide flow rate (ϕCO2), temperature (T), and pressure (P) on ethanol removal performance. Bench-scale assays were performed using a 2-L bubble column containing 10 % v/v ethanol solution, with monitoring of the gas and liquid phases by FT-MIR spectroscopy. The ethanol entrainment factor (FE) increased with ϕCO2 and temperature, but decreased at higher pressure. Only ϕCO2 had significant and positive effects on the concentration factor (FC) and selectivity (αE/W), within the operating ranges of the variables studied. An ethanol removal model was obtained that provided an accurate description of the process behavior, with good agreement between the experimental and simulated data. In addition, the energy requirement for ethanol removal by vacuum-assisted gas stripping in the bioreactor was lower than for the conventional stripping process.
Display omitted
The interest in pneumatic bioreactors is related to their good mass transfer capacity, as well as lower operating costs, due to the simple mechanical structure. Knowledge of the transport phenomena ...and hydrodynamics of bioreactors is important to enable definition of the best bioreactor model and operating conditions for a specific bioprocess, with the imposed shear being one of the most difficult to quantify. For stirred tanks, the fragmentation of microorganisms has been well correlated with a hydrodynamic parameter called the “energy dissipation/circulation function” (EDCF). However, there have been no estimates of the EDCF for pneumatic bioreactors. The present work proposes a methodology to estimate the EDCF for different pneumatic bioreactors and operating conditions using two approaches: Computational Fluid Dynamics and, comparison of pellet fragmentation in conventional and pneumatic bioreactors. First, the volume of higher energy dissipation was estimated in 5 L pneumatic bioreactors, exhibiting values ranging from 57.9 to 106.5 cm³ . Subsequently, EDCF values were estimated, ranging from 0.71 to 9.1 kW·m−3·s−1 for pneumatic bioreactors. Finally, these values were validated by pellet fragmentation assays in stirred tank and pneumatic bioreactors under conditions of similar fragmentation, that resulted in similar EDCF values.
Display omitted
Endoglucanase and xylanase are critical enzymes for liquefaction and enzyme hydrolysis of high solids lignocellulosic biomass to facilitate its transport and production of desired derived products. ...Here is reported how combinations of different spore concentrations and pH influence microbial morphology, and how this may be used to direct expression and secretion of enzymes by Aspergillus niger. While xylanase production is not affected by A. niger morphology changes, endoglucanase production is enhanced under conditions of lower stress and by morphology that results in pellets. β-glucosidase production is enhanced under dispersed morphology, which results in up to fourfold increase of this enzyme production under the tested experimental conditions. A morphologic scale (Y) is proposed based on a form factor that considers the size and frequency of each morphology class, and that points to conditions that result in high selectivity for either endoglucanase orβ-glucosidase production. Further, an equation proposed to relate enzyme activity to morphology provides a useful tool for tuning enzyme production of A. niger, where morphology is a first indication of relative enzyme activities in a fermentation broth.
The manner in which added non-catalytic proteins during enzymatic hydrolysis of lignocellulosic substrates enhances hydrolysis mechanisms is not completely understood. Prior research has indicated ...that a reduction in the non-specific adsorption of enzymes on lignin, and deactivation of enzymes exposed to air–liquid interface provide rationale. This work investigated root causes including effects of the air–liquid interface on non-catalytic proteins, and effects of lignin on endoglucanase. Three different experimental designs and three variables (air–liquid interfacial area, the types of lignin (acid or enzymatic lignin), and the presence of non-enzymatic protein (bovine serum albumin BSA or soy proteins ) were used. The results showed that acid isolated lignin adsorbed almost all endoglucanase activity initially present in supernatant, independent of air interface conditions (25 or 250 ml flasks) with the presence of BSA preventing this effect. Endoglucanase lost 30%–50% of its activity due to an air–liquid interface in the presence of lignin while addition of non-enzymatic protein helped to preserve this enzyme's activity. Langmuir and Freundlich models applied to experimental data indicated that the adsorption increases with increasing temperature for both endoglucanase and BSA. Adsorption of the enzyme and protein were endothermic with an increase in entropy. Finally, these results, combined, show that hydrophobicity plays a strong role in the adsorption of both endoglucanase and BSA on lignin.
