Relation between pellet fragmentation kinetics and cellulolytic enzymes production by Aspergillus niger in conventional bioreactor with different impellers

Effect of impeller type on cellular morphology and production of clavulanic acid by Streptomyces clavuligerus

It is essential to evaluate the effects of operating conditions in submerged cultures of filamentous microorganisms. In particular, the impeller type influences the flow pattern, power consumption, and energy dissipation, leading to differences in the hydrodynamic environment that affect the morphology of the microorganism. This work investigated the effect of different impeller types, namely the Rushton turbine (RT-RT) and Elephant Ear impellers in up-pumping (EEUP) and down-pumping (EEDP) modes, on cellular morphology and clavulanic acid (CA) production by Streptomyces clavuligerus in a stirred-tank bioreactor. At 800 rpm and 0.5 vvm, the cultivations performed using RT-RT and EEUP impellers provided higher shear conditions and oxygen transfer rates than those observed with EEDP. These conditions resulted in higher clavulanic acid production using RT-RT (380.7 mg/L) and EEUP (453.3 mg/L) impellers, compared to EEDP (196.6 mg/L). Although the maximum CA concentration exhibited the same order of magnitude for RT-RT and EEUP impellers, the latter presented 40% of the specific power consumption (4.9 kW/m3) compared to the classical RT-RT (12.0 kW/m3). The specific energy for CA production ( E CA ), defined as the energy cost to produce 1 mg of CA, was 3.5 times lower using the EEUP impeller (1.91 kJ/mgCA) when compared to RT-RT (5.91 kJ/mgCA). Besides, the specific energy for O2 transfer ( E O 2 ), the energy required to transfer 1 mmol of O2, was 2.3 times lower comparing the EEUP impeller (3.28 kJ/mmolO2) to RT-RT (7.65 kJ/mmolO2). The results demonstrated the importance of choosing the most suitable impeller configuration in conventional bioreactors to manufacture bioproducts.

Synchrotron radiation-based microcomputed tomography for three-dimensional growth analysis of Aspergillus niger pellets

Filamentous fungi produce a wide range of relevant biotechnological compounds. The close relationship between fungal morphology and productivity has led to a variety of analytical methods to quantify their macromorphology. Nevertheless, only a µ-computed tomography (µ-CT) based method allows a detailed analysis of the 3D micromorphology of fungal pellets. However, the low sample throughput of a laboratory µ-CT limits the tracking of the micromorphological evolution of a statistically representative number of submerged cultivated fungal pellets over time. To meet this challenge, we applied synchrotron radiation-based X-ray microtomography at the Deutsches Elektronen-Synchrotron [German Electron Synchrotron Research Center], resulting in 19,940 3D analyzed individual fungal pellets that were obtained from 26 sampling points during a 48 h Aspergillus niger submerged batch cultivation. For each of the pellets, we were able to determine micromorphological properties such as number and density of spores, tips, branching points, and hyphae. The computed data allowed us to monitor the growth of submerged cultivated fungal pellets in highly resolved 3D for the first time. The generated morphological database from synchrotron measurements can be used to understand, describe, and model the growth of filamentous fungal cultivations.

Kinetic model supported improved and optimized submerged production strategy of cellulase enzyme from newspaper waste biomass

A systematic evaluation of microorganism's potential towards biosynthesis of cellulases from inexpensive lignocellulosic feedstock through appropriate kinetic modelling facilitates understanding, optimization and designing of an effective industrial cellulase enzyme production process. The present study aims to optimize a submerged fungal cultivation strategy for cellulase production from abundantly available newspaper wastes (NPW). A combined pretreatment strategy consisting diluted, 1% (v v^-1) H₂SO₄ followed by 2% (w v^-1) NaOH treatment was highly effective to convert newspaper waste to an effective cellulose-enriched inducer for the production of cellulase. In addition, the composition of the most influential nutrient components like peptone and lactose was optimized with the help of response surface methodology for enhanced cellulase production with maximum activity levels. Maximum cellulase production of 8.64 g L^-1 with 7.82 FPU mL^-1 total activity levels was achieved from optimized composition of pretreated NPW 3.29% (w v^-1), lactose 2.94% (w v^-1) and peptone 1.53% (w v^-1). To analyse intrinsic inhibition effect of the substrate concentration on cellulase production, modified Luedeking-Piret model simulated experiments were further conducted with 1.5% (w/v), 3.29% (w/v) and 4% (w/v) NPW concentrations. The developed kinetic model perfectly captured the trends of biomass production, substrate consumption and adsorption characteristic of cellulase enzyme on its activity during production. The rate constant for cellulase synthesis was evaluated to be increased to 0.040 IU g^-1 h ^-1 at 3.29% (w v^-1) of NPW concentration; however, it was further reduced to 0.024 IU g^-1 h ^-1 at higher NPW concentration of 4% (w v^-1).

Recent advancements in encapsulation of chitosan-based enzymes and their applications in food industry

Enzymes are readily inactivated in harsh micro-environment due to changes in pH, temperature, and ionic strength. Developing suitable and feasible techniques for stabilizing enzymes in food sector is critical for preventing them from degradation. This review provides an overview on chitosan (CS)-based enzymes encapsulation techniques, enzyme release mechanisms, and their applications in food industry. The challenges and future prospects of CS-based enzymes encapsulation were also discussed. CS-based encapsulation techniques including ionotropic gelation, emulsification, spray drying, layer-by-layer self-assembly, hydrogels, and films have been studied to improve the encapsulation efficacy (EE), heat, acid and base stability of enzymes for their applications in food, agricultural, and medical industries. The smart delivery design, new delivery system development, and in vivo releasing mechanisms of enzymes using CS-based encapsulation techniques have also been evaluated in laboratory level studies. The CS-based encapsulation techniques in commercial products should be further improved for broadening their application fields. In conclusion, CS-based encapsulation techniques may provide a promising approach to improve EE and bioavailability of enzymes applied in food industry.HighlightsEnzymes play a critical role in food industries but susceptible to inactivation.Chitosan-based materials could be used to maintain the enzyme activity.Releasing mechanisms of enzymes from encapsulators were outlined.Applications of encapsulated enzymes in food fields was discussed.

From spores to fungal pellets: a new high throughput image analysis highlights the structural development of Aspergillus niger

Many filamentous fungi are exploited as cell factories in biotechnology. Cultivated under industrially relevant submerged conditions, filamentous fungi can adopt different macromorphologies ranging from dispersed mycelia over loose clumps to pellets. Central to the development of a pellet morphology is the agglomeration of spores after inoculation followed by spore germination and outgrowth into a pellet population which is usually very heterogeneous. As the dynamics underlying population heterogeneity are not yet fully understood, we present here a new high-throughput image analysis pipeline based on stereomicroscopy to comprehensively assess the developmental program starting from germination up to pellet formation. To demonstrate the potential of this pipeline, we used data from 44 sampling times harvested during a 48 h submerged batch cultivation of the fungal cell factory Aspergillus niger. The analysis of up to 1700 spore agglomerates and 1500 pellets per sampling time allowed the precise tracking of the morphological development of the overall culture. The data gained were used to calculate size distributions and area fractions of spores, spore agglomerates, spore agglomerates within pellets, pellets, and dispersed mycelia. This approach eventually enables the quantification of culture heterogeneities and pellet breakage. This article is protected by copyright. All rights reserved.

Recent advances in the development of Aspergillus for protein production

Aspergillus had been widely used in the industrial production of recombinant proteins. In addition to the safety and broad substrate utilization spectrum, its efficient post-translational modification and strong protein secretion capacity have significant advantages for developing an excellent protein-producing cell factory in industrial production. However, the difficulties in genetic manipulation of Aspergillus and varying expression levels of different heterologous proteins hampered its further development and application. Recently, the development of CRISPR genome editing and high-throughput screening platforms has facilitated the Aspergillus development of a wide range of modifications and applications. Meanwhile, multi-omics analysis and multiplexed genetic engineering have promoted effective knowledge mining. This paper provides a comprehensive and updated review of these advances, including high-throughput screening, genome editing, protein expression modules, and fermentation optimization. It also highlights and discusses the latest significant progress, aiming to provide a practical guide for implementing Aspergillus as an efficient protein-producing cell factory.

Effects of Impeller Geometry on the 11α-Hydroxylation of Canrenone in Rushton Turbine-Stirred Tanks

The 11α-hydroxylation of canrenone can be catalyzed by Aspergillus ochraceus in bioreactors, where the geometry of the impeller greatly influences the biotransformation. In this study, the effects of the blade number and impeller diameter of a Rushton turbine on the 11α-hydroxylation of canrenone were considered. The results of fermentation experiments using a 50 mm four-blade impeller showed that 3.40% and 11.43% increases in the conversion ratio were achieved by increasing the blade number and impeller diameter, respectively. However, with an impeller diameter of 60 mm, the conversion ratio with a six-blade impeller was 14.42% lower than that with a four-blade impeller. Data from cold model experiments with a large-diameter six-blade impeller indicated that the serious leakage of inclusions and a 22.08% enzyme activity retention led to a low conversion ratio. Numerical simulations suggested that there was good gas distribution and high fluid flow velocity when the fluid was stirred by large-diameter impellers, resulting in a high dissolved oxygen content and good bulk circulation, which positively affected hyphal growth and metabolism. However, a large-diameter six-blade impeller created overly high shear compared to a large-diameter four-blade impeller, thereby decreasing the conversion ratio. The average shear rates of the former and latter cases were 43.25 s^-1 and 35.31 s^-1, respectively. We therefore concluded that appropriate shear should be applied in the 11α-hydroxylation of canrenone. Overall, this study provides basic data for the scaled-up production of 11α-hydroxycanrenone.

Cellulolytic enzymes production guided by morphology engineering

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.