Particle-based production of antibiotic rebeccamycin with Lechevalieria aerocolonigenes

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.

Quantification and modeling of macroparticle-induced mechanical stress for varying shake flask cultivation conditions

In biotechnological processes, filamentous microorganisms are known for their broad product spectrum and complex cellular morphology. Product formation and cellular morphology are often closely linked, requiring a well-defined level of mechanical stress to achieve high product concentrations. Macroparticles were added to shake flask cultures of the filamentous actinomycete Lentzea aerocolonigenes to find these optimal cultivation conditions. However, there is currently no model concept for the dependence of the strength and frequency of the bead-induced stress on the process parameters. Therefore, shake flask simulations were performed for combinations of bead size, bead concentration, bead density and shaking frequency. Contact analysis showed that the highest shear stresses were caused by bead-bottom contacts. Based on this, a newly generated characteristic parameter, the stress area ratio (SAR), was defined, which relates the bead wall shear and normal stresses to the total shear area. Comparison of the SAR with previous cultivation results revealed an optimum pattern for product concentration and mean product-to-biomass related yield coefficient. Thus, this model is a suitable tool for future optimization, comparison and scaling up of shear-sensitive microorganism cultivation. Finally, the simulation results were validated using high-speed recordings of the bead motion on the bottom of the shake flask.

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.

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.

Expanding the application of tryptophan: Industrial biomanufacturing of tryptophan derivatives

Tryptophan derivatives are various aromatic compounds produced in the tryptophan metabolic pathway, such as 5-hydroxytryptophan, 5-hydroxytryptamine, melatonin, 7-chloro-tryptophan, 7-bromo-tryptophan, indigo, indirubin, indole-3-acetic acid, violamycin, and dexoyviolacein. They have high added value, widely used in chemical, food, polymer and pharmaceutical industry and play an important role in treating diseases and improving life. At present, most tryptophan derivatives are synthesized by biosynthesis. The biosynthesis method is to combine metabolic engineering with synthetic biology and system biology, and use the tryptophan biosynthesis pathway of Escherichia coli, Corynebacterium glutamicum and other related microorganisms to reconstruct the artificial biosynthesis pathway, and then produce various tryptophan derivatives. In this paper, the characteristics, applications and specific biosynthetic pathways and methods of these derivatives were reviewed, and some strategies to increase the yield of derivatives and reduce the production cost on the basis of biosynthesis were introduced in order to make some contributions to the development of tryptophan derivatives biosynthesis industry.

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.

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

Filamentous microorganisms are used as molecular factories in industrial biotechnology. In 2007, a new approach to improve productivity in submerged cultivation was introduced: microparticle-enhanced cultivation (MPEC). Since then, numerous studies have investigated the influence of microparticles on the cultivation. Most studies considered MPEC a morphology engineering approach, in which altered morphology results in increased productivity. But sometimes similar morphological changes lead to decreased productivity, suggesting that this hypothesis is not a sufficient explanation for the effects of microparticles. Effects of surface chemistry on particles were paid little attention, as particles were often considered chemically-inert and bioinert. However, metal oxide particles strongly interact with their environment. This review links morphological, physical, and chemical properties of microparticles with effects on culture broth, filamentous morphology, and molecular biology. More precisely, surface chemistry effects of metal oxide particles lead to ion leaching, adsorption of enzymes, and generation of reactive oxygen species. Therefore, microparticles interfere with gene regulation, metabolism, and activity of enzymes. To enhance the understanding of microparticle-based morphology engineering, further interactions between particles and cells are elaborated. The presented description of phenomena occurring in MPEC eases the targeted choice of microparticles, and thus, contributes to improving the productivity of microbial cultivation technology.

Macroparticle-enhanced cultivation of Lentzea aerocolonigenes: Variation of mechanical stress and combination with lecithin supplementation for a significantly increased rebeccamycin production

The actinomycete Lentzea aerocolonigenes produces the antitumor antibiotic rebeccamycin. In previous studies the rebeccamycin production was significantly increased by the addition of glass beads during cultivation in different diameters between 0.5 and 2 mm and the induced mechanical stress by the glass beads was proposed to be responsible for the increased production. Thus, this study was conducted to be a systematic investigation of different parameters for macroparticle addition, such as bead diameter, concentration, and density (glass and ceramic) as well as shaking frequency, for a better understanding of the particle-induced stress on L. aerocolonigenes. The induced stress for optimal rebeccamycin production can be estimated by a combination of stress energy and stress frequency. In addition, the macroparticle-enhanced cultivation of L. aerocolonigenes was combined with soy lecithin addition to further increase the rebeccamycin concentration. With 100 g L^-1 glass beads in a diameter of 969 µm and 5 g L^-1 soy lecithin a concentration of 388 mg L^-1 rebeccamycin was reached after 10 days of cultivation, which corresponds to the highest rebeccamycin concentrations achieved in shake flask cultivations of L. aerocolonigenes stated in literature so far.

Evaluating the effects of microparticle addition on mycelial morphology, natural yellow pigments productivity, and key genes regulation in submerged fermentation of Monascus purpureus

Morphology plays an important role in fungal fermentation and secondary metabolites biosynthesis. One novel technique, microparticle-enhanced cultivation was successfully utilized to control the morphology of Monascus purpureus precisely and enhance the yield of yellow pigments. The production of yellow pigments increased to 554.2 U/ml when 4 g/L 5000 mesh talc added at 24 h. Field emission scanning electron microscope observation indicated that the actual effect depends on the properties of microparticle. Sharp-edged microparticles showed better stimulatory effects than smooth, round-shaped ones. Particle size analysis, scanning electron microscope, and cell integrity evaluation proved obvious morphological changes were induced by talc addition, including smaller mycelial size, rougher hyphae, and decreased cell integrity. Furthermore, the expression levels of MrpigG, MrpigD, MrpigE, and MrpigH were significantly upregulated by the addition of talc. It indicated that the microparticle could not only affect the mycelial morphology, but also influence the expression levels of key genes in biosynthetic pathway of Monascus yellow pigments.

Challenges of influencing cellular morphology by morphology engineering techniques and mechanical induced stress on filamentous pellet systems-A critical review

Filamentous microorganisms are main producers of organic acids, enzymes, and pharmaceutical agents such as antibiotics and other active pharmaceutical ingredients. With their complex cell morphology, ranging from dispersed mycelia to dense pellets, the cultivation is challenging. In recent years, various techniques for tailor-made cell morphologies of filamentous microorganisms have been developed to increase product formation and have been summarised under the term morphology engineering. These techniques, namely microparticle-enhanced cultivation, macroparticle-enhanced cultivation, and alteration of the osmolality of the culture medium by addition of inorganic salts, the salt-enhanced cultivation, are presented and discussed in this review. These techniques have already proven to be useful and now await further proof-of-concept. Furthermore, the mechanical behaviour of individual pellets is of special interest for a general understanding of pellet mechanics and the productivity of biotechnological processes with filamentous microorganisms. Correlating them with substrate uptake and finally with productivity would be a breakthrough not to be underestimated for the comprehensive characterisation of filamentous systems. So far, this research field is under-represented. First results on filamentous pellet mechanics are discussed and important future aspects, which the filamentous expert community should deal with, will be presented and critically discussed.

Microparticles globally reprogram Streptomyces albus toward accelerated morphogenesis, streamlined carbon core metabolism, and enhanced production of the antituberculosis polyketide pamamycin

Streptomyces spp. are a rich source for natural products with recognized industrial value, explaining the high interest to improve and streamline the performance of in these microbes. Here, we studied the production of pamamycins, macrodiolide homologs with a high activity against multiresistant pathogenic microbes, using recombinant Streptomyces albus J1074/R2. Talc particles (hydrous magnesium silicate, 3MgO·4SiO₂ ·H₂ O) of micrometer size, added to submerged cultures of the recombinant strain, tripled pamamycin production up to 50 mg/L. Furthermore, they strongly affected morphology, reduced the size of cell pellets formed by the filamentous microbe during the process up to sixfold, and shifted the pamamycin spectrum to larger derivatives. Integrated analysis of transcriptome and precursor (CoA thioester) supply of particle-enhanced and control cultures provided detailed insights into the underlying molecular changes. The microparticles affected the expression of 3,341 genes (56% of all genes), revealing a global and fundamental impact on metabolism. Morphology-associated genes, encoding major regulators such as SsgA, RelA, EshA, Factor C, as well as chaplins and rodlins, were found massively upregulated, indicating that the particles caused a substantially accelerated morphogenesis. In line, the pamamycin cluster was strongly upregulated (up to 1,024-fold). Furthermore, the microparticles perturbed genes encoding for CoA-ester metabolism, which were mainly activated. The altered expression resulted in changes in the availability of intracellular CoA-esters, the building blocks of pamamycin. Notably, the ratio between methylmalonyl CoA and malonyl-CoA was increased fourfold. Both metabolites compete for incorporation into pamamycin so that the altered availability explained the pronounced preference for larger derivatives in the microparticle-enhanced process. The novel insights into the behavior of S. albus in response to talc appears of general relevance to further explore and upgrade the concept of microparticle enhanced cultivation, widely used for filamentous microbes.

Morphological and physiological characterization of filamentous Lentzea aerocolonigenes: Comparison of biopellets by microscopy and flow cytometry

Cell morphology of filamentous microorganisms is highly interesting during cultivations as it is often linked to productivity and can be influenced by process conditions. Hence, the characterization of cell morphology is of major importance to improve the understanding of industrial processes with filamentous microorganisms. For this purpose, reliable and robust methods are necessary. In this study, pellet morphology and physiology of the rebeccamycin producing filamentous actinomycete Lentzea aerocolonigenes were investigated by microscopy and flow cytometry. Both methods were compared regarding their applicability. To achieve different morphologies, a cultivation with glass bead addition (Ø = 969 μm, 100 g L-1) was compared to an unsupplemented cultivation. This led to two different macro-morphologies. Furthermore, glass bead addition increased rebeccamycin titers after 10 days of cultivation (95 mg L-1 with glass beads, 38 mg L-1 without glass beads). Macro-morphology and viability were investigated through microscopy and flow cytometry. For viability assessment fluorescent staining was used additionally. Smaller, more regular pellets were found for glass bead addition. Pellet diameters resulting from microscopy followed by image analysis were 172 μm without and 106 μm with glass beads, diameters from flow cytometry were 170 and 100 μm, respectively. These results show excellent agreement of both methods, each considering several thousand pellets. Furthermore, the pellet viability obtained from both methods suggested an enhanced metabolic activity in glass bead treated pellets during the exponential production phase. However, total viability values differ for flow cytometry (0.32 without and 0.41 with glass beads) and confocal laser scanning microscopy of single stained pellet slices (life ratio in production phase of 0.10 without and 0.22 with glass beads), which is probably caused by the different numbers of investigated pellets. In confocal laser scanning microscopy only one pellet per sample could be investigated while flow cytometry considered at least 50 pellets per sample, resulting in an increased statistical reliability.

Salt-enhanced cultivation as a morphology engineering tool for filamentous actinomycetes: Increased production of labyrinthopeptin A1 in Actinomadura namibiensis

Salt-enhanced cultivation as a morphology engineering tool for the filamentous actinomycete Actinomadura namibiensis was evaluated in 500-mL shaking flasks (working volume 100 mL) with the aim of increasing the concentration of the pharmaceutically interesting peptide labyrinthopeptin A1. Among the inorganic salts added to a complex production medium, the addition of (NH₄)₂SO₄ led to the highest amount of labyrinthopeptin A1 production. By using 50 mM (NH₄)₂SO₄, the labyrinthopeptin A1 concentration increased up to sevenfold compared to the non-supplemented control, resulting in 325 mg L^-1 labyrinthopeptin A1 after 10 days of cultivation. The performance of other ammonium- and sulfate-containing salts (e.g., NH₄Cl, K₂SO₄) was much lower than the performance of (NH₄)₂SO₄. A positive correlation between the uptake of glycerol as one of the main carbon sources and nongrowth-associated labyrinthopeptin productivity was found. The change in the cell morphology of A. namibiensis in conjunction with increased osmolality by the addition of 50 mM (NH₄)₂SO₄, was quantified by image analysis. A. namibiensis always developed a heterogeneous morphology with pellets and loose mycelia present simultaneously. In contrast to the non-supplemented control, the morphology of (NH₄)₂SO₄-supplemented cultures was characterized by smaller and circular pellets that were more stable against disintegration in the stationary production phase.

The antitumor antibiotic rebeccamycin-challenges and advanced approaches in production processes

Rebeccamycin is an antibiotic and antitumor substance isolated from the filamentous bacterium Lentzea aerocolonigenes. After its discovery, investigations of rebeccamycin focused on elucidating its structure, biological activity, and biosynthetic pathway. For potential medical application, a sufficient drug supply has to be ensured, meaning that the production process of rebeccamycin plays a major role. In addition to the natural production of rebeccamycin in L. aerocolonigenes, where the complex cell morphology is an important factor for a sufficient production, rebeccamycin can also be heterologously produced or chemically synthesized. Each of these production processes has its own challenges, and first approaches to production often lead to low final product concentrations, which is why process optimizations are performed. This review provides an overview of the production of rebeccamycin and the different approaches used for rebeccamycin formation including process optimizations.

Microtiter plate-based cultivation to investigate the growth of filamentous fungi

Microscale bioprocessing techniques are rapidly emerging as a means to increase the speed of bioprocess design and to reduce material consumption. However, there is still a lack of suitable parallelized techniques to investigate the industrially important group of filamentous bacteria and fungi. Cultivation of filamentous organisms in shake flasks is still the favored technique for comparing and optimizing cultivation conditions of production strains at mL-scale. In this paper, the application of a microtiter plate-based cultivation system in combination with the filamentous fungus Aspergillus niger was investigated. A protocol for reproducible cultivation was developed and evaluated. Productivity of A. niger concerning the rose-like aroma compound 2-phenylethanol showed low standard deviations while regular and consistent morphologies appeared in the parallelized system. Furthermore, the effect of addition of microparticles on the morphology was investigated. The results can be used to accelerate the process development with A. niger and other filamentous organisms.