Effects and interactions of metal oxides in microparticle-enhanced cultivation of filamentous microorganisms

Oxygen Consumption in Filamentous Pellets of Aspergillus niger: Microelectrode Measurements and Modeling

Filamentous fungi cultivated as biopellets are well established in biotechnology industries. A distinctive feature of filamentous fungi is that hyphal growth and fungal morphology affect product titers and require tailored process conditions. Within the pellet, mass transfer, substrate consumption, and biomass formation are intricately linked to the local hyphal fraction and pellet size. This study combined oxygen concentration measurements with microelectrode profiling and three-dimensional X-ray microtomography measurements of the same fungal pellets for the first time. This allowed for the precise correlation of micromorphological information with local oxygen concentrations of two Aspergillus niger strains (hyperbranching and regular branching). The generated results showed that the identified oxygen-penetrated outer pellet regions exhibited a depth of 90-290 µm, strain-specific, with the active part percentage in the pellet ranging from 18% to 69%, without any difference between strains. Using a 1D continuum diffusion consumption model, the oxygen concentration in the pellets was computed depending on the local hyphal fraction. The best simulation results were achieved by individually estimating the oxygen-related biomass yield coefficient of the consumption term within each examined pellet, with an average estimated value of 1.95 (± 0.72) kg biomass per kg oxygen. The study lays the foundation for understanding oxygen supply in fungal pellets and optimizing processes and pellet morphologies accordingly.

3D imaging and analysis to unveil the impact of microparticles on the pellet morphology of filamentous fungi

Controlling the morphology of filamentous fungi is crucial to improve the performance of fungal bioprocesses. Microparticle-enhanced cultivation (MPEC) increases productivity, most likely by changing the fungal morphology. However, due to a lack of appropriate methods, the exact impact of the added microparticles on the structural development of fungal pellets is mostly unexplored. In this study synchrotron radiation-based microcomputed tomography and three-dimensional (3D) image analysis were applied to unveil the detailed 3D incorporation of glass microparticles in nondestructed pellets of Aspergillus niger from MPEC. The developed method enabled the 3D analysis based on 375 pellets from various MPEC experiments. The total and locally resolved volume fractions of glass microparticles and hyphae were quantified for the first time. At increasing microparticle concentrations in the culture medium, pellets with lower hyphal fraction were obtained. However, the total volume of incorporated glass microparticles within the pellets did not necessarily increase. Furthermore, larger microparticles were less effective than smaller ones in reducing pellet density. However, the total volume of incorporated glass was larger for large microparticles. In addition, analysis of MPEC pellets from different times of cultivation indicated that spore agglomeration is decisive for the development of MPEC pellets. The developed 3D morphometric analysis method and the presented results will promote the general understanding and further development of MPEC for industrial application.

Analysis of secondary metabolites and morphology in Streptomyces rimosus microparticle-enhanced cultivation (MPEC) at various initial organic nitrogen concentrations

The influence of talc microparticles on metabolism and morphology of S. rimosus at various initial organic nitrogen concentrations was investigated. The shake flask cultivations were conducted in the media with yeast extract (nitrogen source) concentration equal to 1 g YE L- 1 and 20 g YE L- 1. Two talc microparticle concentrations of 5 g TALC L- 1 and 10 g TALC L- 1 were tested in microparticle-enhanced cultivation (MPEC) runs. A high nitrogen concentration of 20 g YE L- 1 promoted the development of small agglomerates (pellets) of projected area lower than 105 µm2 and dispersed pseudohyphae. A low nitrogen concentration of 1 g YE L- 1 led to the limitation of S. rimosus growth and, in consequence, the development of the smaller number of large pseudohyphal agglomerates (pellets) of projected area higher than 105 µm2 compared to the culture containing a high amount of nitrogen source. In both cases talc microparticles were embedded into pellets and caused the decrease in their sizes. The lower amount of talc (5 g TALC L- 1) usually caused the weaker effect on S. rimosus morphology and metabolite production than the higher one. This correlation between the microparticles effect on morphology and metabolism of S. rimosus was especially noticeable in the biosynthesis of oxytetracycline, 2-acetyl-2-dicarboxamide oxytetracycline (ADOTC) and spinoxazine A. Compared to the control run, in MPEC their levels increased 4-fold, 5-fold and 1.6-fold respectively. The addition of talc also improved the production of 2-methylthio-cis-zeatin, lorneic acid J and milbemycin A3.

Morphological-metabolic analysis in Streptomyces rimosus microparticle-enhanced cultivations (MPEC)

Streptomyces produce a broad spectrum of biologically active molecules such as oxytetracycline and rimocidin, which are widely used in human and animal treatments. microparticle-enhanced cultivation (MPEC) is one of the tools used for Streptomyces bioprocesses intensification by the control of mycelial morphology. In the present work, morphological changes of Streptomyces rimosus caused by the addition of 10 µm talc microparticles in MPEC were correlated with the biosynthetic activity of the microorganism. Comparing the runs with and without microparticles, major morphological changes were observed in MPEC, including the deformation of pellets, variation of their size, appearance of hyphae and clumps as well as the aggregation of mycelial objects. The presence of talc microparticles also influenced the levels of the studied secondary metabolites produced by S. rimosus. Comparing control and MPEC runs, the addition of talc microparticles increased the amounts of oxytetracycline (9-fold), 2-acetyl-2-decarboxamido-oxytetracycline (7-fold), milbemycin A3+4[O] (3-fold) and CE 108 (1.5-fold), while rimocidin (27-ethyl) and milbemycin β11+4[O] production was reduced. In summary, the addition of talc microparticles to S. rimosus cultivations led to the development of smaller morphological forms like hyphae and clumps as well as to the changes in the amounts of secondary metabolites.

Exopolysaccharides produced by Antrodia cinnamomea using microparticle-enhanced cultivation: Optimization, primary structure and antibacterial property

Microparticle-enhanced cultivation was used to enhance the production of exopolysaccharides (EPSs) from Antrodia cinnamomea. The structure and antibacterial activity of two EPSs produced by A. cinnamomea treated with Al2O3 [EPS-Al (crude) and EPS-Al-p (purified)] and without Al2O3 [EPS-C (crude) and EPS-C-p (purified)] were compared. It was observed that the addition of 4 g/L Al2O3 at 0 h resulted in the highest EPS yield of 1.46 g/L, possible attributed to the enhanced permeability of the cell membrane. The structural analysis revealed that EPS-C-p and EPS-Al-p had different structures. EPS-C-p was hyperbranched and spherical with a Mw of 10.8 kDa, while EPS-Al-p was irregular and linear with a Mw of 12.5 kDa. The proportion of Man in EPS-Al-p decreased, while those of Gal and Glc increased when compared to EPS-C-p. The total molar ratios of 6-Glcp and 4-Glcp in EPS-Al-p are 1.45 times that of EPS-C-p. Moreover, EPSs could alter bacterial cell morphology, causing intracellular substance leakage and growth inhibition, with EPS-Al having a stronger antibacterial activity than EPS-C. In conclusion, A. cinnamomea treated with Al2O3 could produce more EPSs, changing monosaccharide composition and glycosidic linkage profile, which could exert stronger antibacterial activity than that produced by untreated A. cinnamomea.

Genome-guided approaches and evaluation of the strategies to influence bioprocessing assisted morphological engineering of Streptomyces cell factories

Streptomyces genera serve as adaptable cell factories for secondary metabolites with various and distinctive chemical structures that are relevant to the pharmaceutical industry. Streptomyces' complex life cycle necessitated a variety of tactics to enhance metabolite production. Identification of metabolic pathways, secondary metabolite clusters, and their controls have all been accomplished using genomic methods. Besides this, bioprocess parameters were also optimized for the regulation of morphology. Kinase families were identified as key checkpoints in the metabolic manipulation (DivIVA, Scy, FilP, matAB, and AfsK) and morphology engineering of Streptomyces. This review illustrates the role of different physiological variables during fermentation in the bioeconomy coupled with genome-based molecular characterization of biomolecules responsible for secondary metabolite production at different developmental stages of the Streptomyces life cycle.

Efficient production of Antrodin C by microparticle-enhanced cultivation of medicinal mushroom Antrodia cinnamomea

The microparticle-enhanced cultivation (MPEC) was used to enhance the production of Antrodin C by submerged fermentation of medicinal mushroom Antrodia cinnamomea. The crucial factors such as types, sizes, concentrations, and addition time of microparticles were optimized. The mechanism of MPEC on the membrane permeability and fluidity of A. cinnamomea and the expression of key genes in Antrodin C were investigated. When talc (18 μm, 2 g/L) was added into the fermentation liquid at 0 h, the promoting effect on Antrodin C was the best. The maximum yield of Antrodin C was 1615.7 mg/L, which was about 2.98 times of the control (541.7 mg/L). Talc slightly damaged the mycelia of A. cinnamomea, increased the release of intracellular constituents, and enhanced the index of unsaturated fatty acid. In addition, the key genes (IDI, E2.3.3.10, HMGCR, atoB) that might play an important role in the synthesis of the triquine-type sesquiterpene Antrodin C, were upregulated. In conclusion, talc increased the permeability and fluidity of cell membrane, upregulated the key genes and improved the biosynthesis process to enhance the yield of Antrodin C in the submerged fermentation of A. cinnamomea.

Intensification of bioprocesses with filamentous microorganisms

Many industrial biotechnological processes use filamentous microorganisms to produce platform chemicals, proteins, enzymes and natural products. Product formation is directly linked to their cellular morphology ranging from dispersed mycelia over loose clumps to compact pellets. Therefore, the adjustment and control of the filamentous cellular morphology pose major challenges for bioprocess engineering. Depending on the filamentous strain and desired product, optimal morphological shapes for achieving high product concentrations vary. However, there are currently no overarching strain- or product-related correlations to improve process understanding of filamentous production systems. The present book chapter summarizes the extensive work conducted in recent years in the field of improving product formation and thus intensifying biotechnological processes with filamentous microorganisms. The goal is to provide prospective scientists with an extensive overview of this scientifically diverse, highly interesting field of study. In the course of this, multiple examples and ideas shall facilitate the combination of their acquired expertise with promising areas of future research. Therefore, this overview describes the interdependence between filamentous cellular morphology and product formation. Moreover, the currently most frequently used experimental techniques for morphological structure elucidation will be discussed in detail. Developed strategies of morphology engineering to increase product formation by tailoring and controlling cellular morphology and thus to intensify processes with filamentous microorganisms will be comprehensively presented and discussed.

Morphology engineering for novel antibiotics: Effect of glass microparticles and soy lecithin on rebeccamycin production and cellular morphology of filamentous actinomycete Lentzea aerocolonigenes

Lentzea aerocolonigenes, as an actinomycete, is a natural producer of the antibiotic and antitumoral drug rebeccamycin. Due to the filamentous cellular morphology handling in cultivations is challenging; therefore, morphology engineering techniques are mandatory to enhance productivity. One promising approach described in the literature is the addition of mineral particles in the micrometer range to precisely adjust cellular morphology and the corresponding product synthesis (microparticle-enhanced cultivation, MPEC). Glass microparticles are introduced in this study as a novel supplementation type for bioprocess intensification in filamentous organisms. Several investigations were conducted to screen for an optimal particle setup, including particle size and concentration regarding their impact and effects on enhanced productivity, microparticle incorporation behavior into the biopellets, the viability of pellets, and morphological changes. Glass microparticles (10 g·L^-1) with a median diameter of 7.9 µm, for instance, induced an up to fourfold increase in product synthesis accompanied by overall enhanced viability of biomass. Furthermore, structural elucidations showed that biopellets isolated from MPEC tend to have lower hyphal density than unsupplemented control pellets. In this context, oxygen microprofiling was conducted to better understand how internal structural changes interwind with oxygen supply into the pellets. Here, the resulting oxygen profiles are of a contradictive trend of steeper oxygen consumption with increasing glass microparticle supplementation. Eventually, MPEC was combined with another promising cultivation strategy, the supplementation of soy lecithin (7.5 g·L^-1), to further increase the cultivation performance. A combination of both techniques in an optimized setup resulted in a rebeccamycin concentration of 213 mg·L^-1 after 10 days of cultivation, the highest value published so far for microparticle-supplemented shake flask cultivations of L. aerocolonigenes.

Influence of Bacillus subtilis on the surface behavior and separation of talc and chlorite minerals

Bacillus subtilis was used as a bio-surface modifier to improve the floatability of talc mineral (Mg3Si4O10(OH)2) in the talc ore. The surface behavior of chlorite mineral as the main associated gangue with talc mineral was studied in the presence of B. subtilis using zeta potential, scanning electron microscopy, and Fourier-transform infrared spectroscopy techniques. The floatability of both minerals was investigated as a function of pH, contact time, and concentration of B. subtilis. The results showed that the zeta potential of the talc mineral was strongly influenced by the treatment with B. subtilis. The maximum separation efficiency of talc from chlorite was achieved at pH 4. A talc concentrate with 98% quality and about 95% recovery was prepared from a binary talc-chlorite mixture containing 85% talc under optimum conditions of 8 × 105 cells/mL B. subtilis, pH 4, 35°C, and a contact time of 10 min.

Co-cultivation of filamentous microorganisms in the presence of aluminum oxide microparticles

In the present work, the approaches of submerged co-cultivation and microparticle-enhanced cultivation (MPEC) were combined and evaluated over the course of three case studies. The filamentous fungus Aspergillus terreus was co-cultivated with Penicillium rubens, Streptomyces rimosus, or Cerrena unicolor in shake flasks with or without the addition of aluminum oxide microparticles. The influence of microparticles on the production of lovastatin, penicillin G, oxytetracycline, and laccase in co-cultures was compared with the effects recorded for the corresponding monocultures. In addition, the quantitative analyses of morphological parameters, sugars consumption, and by-products formation were performed. The study demonstrated that the influence of microparticles on the production of a given molecule in mono- and co-culture may differ considerably, e.g., the biosynthesis of oxytetracycline was shown to be inhibited due to the presence of aluminum oxide in "A. terreus vs. S. rimosus" co-cultivation variants but not in S. rimosus monocultures. The differences were also observed regarding the morphological characteristics, e.g., the microparticles-induced changes of projected area in the co-cultures and the corresponding monocultures were not always comparable. In addition, the study showed the importance of medium composition on the outcomes of MPEC, as exemplified by lovastatin production in A. terreus monocultures. Finally, the co-cultures of A. terreus with a white-rot fungus C. unicolor were described here for the first time. KEY POINTS: • Aluminum oxide affects secondary metabolites production in submerged co-cultures. • Mono- and co-cultures are differently impacted by the addition of aluminum oxide. • Effect of aluminum oxide on metabolites production depends on medium composition.

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.