The filamentous fungal pellet-relationship between morphology and productivity

Increasing-Aeration Strategy: a Practical Approach to Enhance the Schizophyllan Production and Improve the Operational Conditions of Schizophyllum commune Cultivation in the Stirred Tank and Bubble Column Bioreactors

In the present study, the effect of employing the increasing- aeration strategy (IAS) in the oxygen-limited situation and proportionate to increasing oxygen demand of the fungus Schizophyllum commune (S. commune) has been investigated in both stirred tank (STB) and bubble column (BCB) bioreactors. The purpose was to enhance schizophyllan (SPG) production by preventing oxygen starvation, improve mixing conditions of pseudoplastic culture, and intensify shear stress on fungus pellets to release SPG. At first, a constant-aeration rate of 0.08 vvm was implemented in both bioreactors to evaluate the new strategy compared to the previously studied methods. In the second set of experiments with IAS, along with the increasing oxygen demand of culture, the inlet airflow was increased gradually, while the dissolved oxygen (DO) was maintained higher than zero and below 1%. Using IAS in STB significantly raised productivity by about 100% in 96 h from 0.035 to 0.073 g/L.h. Also, employing this strategy in BCB led to a 30% increase in the maximum SPG production from 3.2 to 4.2 g/L. IAS can effectively help handle the operation of S. commune cultivation on a large scale by improving mixing conditions, mass transfer, and shear stress in both bioreactor types. This method had a significant impact on STB cultivation and its productivity so that it can be a practical approach to SPG's industrial production.

Transcriptomic Analysis of Morphology Regulatory Mechanisms of Microparticles to Paraisaria dubia in Submerged Fermentation

Liquid submerged fermentation is an effective strategy to achieve large-scale production of active ingredients by macrofungi, and controlling mycelium morphology is a key factor restricting the development of this technology. Mining for superior morphological regulatory factors and elucidation of their regulatory mechanisms are vital for the further development of macrofungal fermentation technology. In this study, microparticles were used to control the morphology of Paraisaria dubia (P. dubia) in submerged fermentation, and the underlying regulatory mechanisms were revealed by transcriptomic. The relative frequency of S-type pellet diameter increased significantly from 7.14 to 88.31%, and biomass increased 1.54 times when 15 g/L talc was added. Transcriptome analysis showed that the morphological regulation of filamentous fungi was a complex biological process, which involved signal transduction, mycelium polar growth, cell wall synthesis and cell division, etc. It also showed a positive impact on the basic and secondary metabolism of P. dubia. We provided a theoretical basis for controlling the mycelium morphology of P. dubia in submerged fermentation, which will promote the development of macrofungal fermentation technology.

A Library of Aspergillus niger Chassis Strains for Morphology Engineering Connects Strain Fitness and Filamentous Growth With Submerged Macromorphology

Submerged fermentation using filamentous fungal cell factories is used to produce a diverse portfolio of useful molecules, including food, medicines, enzymes, and platform chemicals. Depending on strain background and abiotic culture conditions, different macromorphologies are formed during fermentation, ranging from dispersed hyphal fragments to approximately spherical pellets several millimetres in diameter. These macromorphologies are known to have a critical impact on product titres and rheological performance of the bioreactor. Pilot productivity screens in different macromorphological contexts is technically challenging, time consuming, and thus a significant limitation to achieving maximum product titres. To address this bottleneck, we developed a library of conditional expression mutants in the organic, protein, and secondary metabolite cell factory Aspergillus niger. Thirteen morphology-associated genes transcribed during fermentation were placed via CRISPR-Cas9 under control of a synthetic Tet-on gene switch. Quantitative analysis of submerged growth reveals that these strains have distinct and titratable macromorphologies for use as chassis during strain engineering programs. We also used this library as a tool to quantify how pellet formation is connected with strain fitness and filamentous growth. Using multiple linear regression modelling, we predict that pellet formation is dependent largely on strain fitness, whereas pellet Euclidian parameters depend on fitness and hyphal branching. Finally, we have shown that conditional expression of the putative kinase encoding gene pkh2 can decouple fitness, dry weight, pellet macromorphology, and culture heterogeneity. We hypothesize that further analysis of this gene product and the cell wall integrity pathway in which it is embedded will enable more precise engineering of A. niger macromorphology in future.

Heterologous Expression of Fungal Biosynthetic Pathways in Aspergillus nidulans Using Episomal Vectors

Filamentous fungi produce a wide diversity of secondary metabolites, whose biosynthesis is encoded in biosynthetic gene clusters (BGCs). As novel BGCs are often found in fungal species that are genetically intractable or difficult to cultivate, heterologous expression is increasingly being used for compound discovery. In addition, heterologous expression is a useful strategy to elucidate the function of the genes within a BGC and shed light on their enzymatic mechanisms. Here, we describe a method for BGC elucidation using multi-marker AMA1-based pYFAC vectors for episomal expression in the fungal host Aspergillus nidulans. The pYFAC vectors have the advantage of high transformation efficiency and support high compound production. In addition, different pathway intermediates can be easily evaluated by testing different vector combinations. This protocol encompasses different AMA1-based strategies for BGC expression such as cloning of a BGC native sequence, promoter exchange or transcription factor overexpression. We also describe procedures for A. nidulans protoplasting, transformation, and small-scale culture analysis of strains containing AMA1 vectors.

Rapid and concise quantification of mycelial growth by microscopic image intensity model and application to mass cultivation of fungi

The microbial food fermentation industry requires real-time monitoring and accurate quantification of cells. However, filamentous fungi are difficult to quantify as they have complex cell types such as pellet, spores, and dispersed hyphae. In this study, numerous data of microscopic image intensity (MII) were used to develop a simple and accurate quantification method of Cordyceps mycelium. The dry cell weight (DCW) of the sample collected during the fermentation was measured. In addition, the intensity values were obtained through the ImageJ program after converting the microscopic images. The prediction model obtained by analyzing the correlation between MII and DCW was evaluated through a simple linear regression method and found to be statistically significant (R2 = 0.941, p < 0.001). In addition, validation with randomly selected samples showed significant accuracy, thus, this model is expected to be used as a valuable tool for predicting and quantifying fungal growth in various industries.

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.

Simultaneous Biological Pretreatment and Saccharification of Rice Straw by Ligninolytic Enzymes from Panus neostrigosus I9 and Commercial Cellulase

The utilization of rice straw for biofuel production is limited by its composition. The pretreatment process is required to improve the enzymatic accessibility of polysaccharides in the biomass prior to enzymatic saccharification. In this study, simultaneous biological pretreatment and saccharification (SPS) of rice straw starting from laccase production by Panus neostrigosus I9 was operated in a 2-L fermenter. It was found that fungal physiology was strongly influenced by the agitation, and that the highest laccase production was obtained at an agitation speed of 750 rpm (209.96 ± 0.34 U/L). The dilution rate of 0.05 h-1 was set in continuous fermentation which resulted in laccase activity of 678.49 ± 20.39 U/L, approximately three times higher than that in batch culture. Response surface methodology (RSM) was applied to achieve the condition for maximum percentage of delignification. The maximum percentage of delignification of 45.55% was accomplished after pretreatment of rice straw with laccase enzyme 39.40 U/g rice straw at 43.70 °C for 11.19 h. Reducing sugar of 3.85 ± 0.15 g/L was obtained from the digested rice straw in a SPS reactor, while non-pretreated rice straw gave only 1.13 ± 0.10 g/L within 12 h of incubation. The results indicated that simultaneous biological pretreatment and saccharification (SPS) of rice straw by laccase helped to improve the accessibility of cellulose by cellulolytic enzymes.

Bioprocess Optimisation for High Cell Density Endoinulinase Production from Recombinant Aspergillus niger

Endoinulinase gene was expressed in recombinant Aspergillus niger for selective and high-level expression using an exponential fed-batch fermentation. The effects of the growth rate (μ), glucose feed concentration, nitrogen concentration and fungal morphology on enzyme production were evaluated. A recombinant endoinulinase with a molecular weight of 66 kDa was secreted. Endoinulinase production was growth associated at μ> 0.04 h-1, which is characteristic of the constitutive gpd promoter used for the enzyme production. The highest volumetric activity (670 U/ml) was achieved at a growth rate of 93% of μmax (0.07 h-1), while enzyme activity (506 U/ml) and biomass substrate yield (0.043 gbiomassDW/gglucose) significantly decreased at low μ (0.04 h-1). Increasing the feed concentration resulted in high biomass concentrations and viscosity, which necessitated high agitation to enhance the mixing efficiency and oxygen. However, the high agitation and low DO levels (ca. 8% of saturation) led to pellet disruption and growth in dispersed morphology. Enzyme production profiles, product (Yp/s) and biomass (Yx/s) yield coefficients were not affected by feed concentration and morphological change. The gradual increase in the concentration of nitrogen sources showed that, a nitrogen limited culture was not suitable for endoinulinase production in recombinant A. niger. Moreover, the increase in enzyme volumetric activity was still directly related to an increase in biomass concentration. An increase in nitrogen concentration, from 3.8 to 12 g/L, resulted in volumetric activity increase from 393 to 670 U/ml, but the Yp/s (10053 U/gglucose) and Yx/s (0.049 gbiomasDWs/gglucose) did not significantly change. The data demonstrated the potential of recombinant A. niger and high cell density fermentation for the development of large-scale endoinulinase production system.

Expression of F-actin and β-tubulin genes in free mycelia and robust biofilms of the filamentous fungus Aspergillus niger

The morphology and growth of the filamentous fungi are influenced by different factors as the culture conditions and the type of fermentative process. The production and secretion of metabolites by these organisms present a direct relationship with their morphology. The organization of the microtubules and actin in the cytoskeleton is determinant for both the fungal growth and morphology. In this context, this study aimed to analyze the expression of the β-tubulin, F-actin, and glucan synthase in the A. niger mycelia obtained from submerged fermentation and biofilm fermentation through qPCR, as well as the analysis of the nucleus distribution in the hypha. Herein, we showed that β-tubulin and the F-actin gene were more expressed in the biofilm condition, while the glucan synthase was in the submerged condition. No significant difference was observed in the nucleus distribution between the mycelia obtained from both the fermentative processes. In conclusion, the different morphologies observed for the mycelia from submerged fermentation and biofilm fermentation might be influenced by the differential modulation of genes that codify cytoskeleton proteins, which seems to be potentially regulated by mechanosensing during fungal contact with solid supports.

Understanding and controlling filamentous growth of fungal cell factories: novel tools and opportunities for targeted morphology engineering

Filamentous fungal cell factories are efficient producers of platform chemicals, proteins, enzymes and natural products. Stirred-tank bioreactors up to a scale of several hundred m³ are commonly used for their cultivation. Fungal hyphae self-assemble into various cellular macromorphologies ranging from dispersed mycelia, loose clumps, to compact pellets. Development of these macromorphologies is so far unpredictable but strongly impacts productivities of fungal bioprocesses. Depending on the strain and the desired product, the morphological forms vary, but no strain- or product-related correlations currently exist to improve process understanding of fungal production systems. However, novel genomic, genetic, metabolic, imaging and modelling tools have recently been established that will provide fundamental new insights into filamentous fungal growth and how it is balanced with product formation. In this primer, these tools will be highlighted and their revolutionary impact on rational morphology engineering and bioprocess control will be discussed.

Influence of Selenium Biofortification on the Growth and Bioactive Metabolites of Ganoderma lucidum

Selenium biofortification of edible and medicinal mushrooms is an effective way to produce selenium-enriched food supplements. Ganoderma lucidum is the typical one with excellent biological activity. This study investigated G. lucidum growth and bioactive metabolites alterations during liquid culture with different concentrations of selenite. Low selenium levels did not affect growth and mycelia morphology, whereas high selenium levels negatively influenced growth, dramatically decreased biomass, caused nucleic acid and protein leakage, damaged cell walls and membranes, and resulted in indicators such as degraded cells, a red color, and an unpleasant odor. Through headspace-solid phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) analysis, ten volatile Se compounds were identified in G. lucidum with 200 ppm selenite, which led to an odor change, whereas only three with 50 ppm selenite. SeMet was the major selenoamino acid in the 50 ppm selenite group by high-performance liquid chromatography-inductively coupled plasma mass spectrometry (HPLC-ICP-MS), but more MeSeCys was produced with 200 ppm selenite. Polysaccharide yields were promoted and inhibited with 50 and 200 ppm selenite, respectively. These results provide comprehensive insights into the effects of selenite on G. lucidum in liquid culture and are beneficial for functional selenium-enriched mushroom production and improving nutritive values.

Something old, something new: challenges and developments in Aspergillus niger biotechnology

The filamentous ascomycete fungus Aspergillus niger is a prolific secretor of organic acids, proteins, enzymes and secondary metabolites. Throughout the last century, biotechnologists have developed A. niger into a multipurpose cell factory with a product portfolio worth billions of dollars each year. Recent technological advances, from genome editing to other molecular and omics tools, promise to revolutionize our understanding of A. niger biology, ultimately to increase efficiency of existing industrial applications or even to make entirely new products. However, various challenges to this biotechnological vision, many several decades old, still limit applications of this fungus. These include an inability to tightly control A. niger growth for optimal productivity, and a lack of high-throughput cultivation conditions for mutant screening. In this mini-review, we summarize the current state-of-the-art for A. niger biotechnology with special focus on organic acids (citric acid, malic acid, gluconic acid and itaconic acid), secreted proteins and secondary metabolites, and discuss how new technological developments can be applied to comprehensively address a variety of old and persistent challenges.

CONTROL DE Aedes aegypti (DIPTERA: CULICIDAE) MEDIANTE ACTINOBACTERIAS FORMADORAS DE BIOPELÍCULAS

El phylum Actinobacteria incluye miembros productores de compuestos bioinsecticidas. No obstante, la sobreexplotacion de metabolitos derivados de Streptomyces ha conllevado a explorar nuevas moléculas provenientes de bacterias no estreptomicetos para contrarrestar la resistencia a insecticidas químicos en Aedes aegypti. Concordantes con el uso de bioagentes ecológicos, esta investigación caracterizó actinobacterias formadoras de biopelículas con el fin de evaluar su dinámica de crecimiento, actividad larvicida y efectos subletales. La identificación, crecimiento de biopelículas y bioactividades se realizaron por cultivos, análisis de imágenes por fotomicrografía y bioensayos. Los resultados mostraron que las biopelículas pertenecen a Pseudonocardiaceae (PsA1TA) y Corynebacteriaceae (CoA2CA) característicamente dependientes del revestimiento cuticular. PsA1TA coloniza estructuras membranosas de tórax y abdomen con microcolonias aleatoriamente distribuidas que desarrollan a extensas biopelículas mono y biestratificadas, al cubrir cuatro veces la amplitud toracoabdominal (envergadura infectiva entre 1010 µm a 1036 µm). En contraste, CoA2CA envuelve radialmente estructuras esclerotizadas cefálica y anal al triplicar la amplitud de tales órganos (1820 a 2030 µm y 1650 a 1860 µm, respectivamente). Las biopelículas ejercieron mortalidad diferenciada a todos los estadios larvales, no obstante, PsA1TA resultó más mortal y virulento en el segundo estadio larval (58 %-96 horas, TL50: 3,4 días), mientras que CoA2CA lo fue en el cuarto estadio larval (85 %-96 horas, TL50: 2,5 días). CoA2CA indujo emergencia incompleta de adultos farados y despliegue de tarsos curvos en emergentes, además de revestir con robustas biopelículas cadáveres larvarios. Las biopelículas actinobacterianas revelaron ejercer función larvicida y respuestas subletales en A. aegypti.

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.

Microparticles enhance the formation of seven major classes of natural products in native and metabolically engineered actinobacteria through accelerated morphological development

Actinobacteria provide a rich spectrum of bioactive natural products and therefore display an invaluable source towards commercially valuable pharmaceuticals and agrochemicals. Here, we studied the use of inorganic talc microparticles (hydrous magnesium silicate, 3MgO·4SiO₂ ·H₂ O, 10 µm) as a general supplement to enhance natural product formation in this important class of bacteria. Added to cultures of recombinant Streptomyces lividans, talc enhanced production of the macrocyclic peptide antibiotic bottromycin A2 and its methylated derivative Met-bottromycin A2 up to 109 mg L^-1 , the highest titer reported so far. Hereby, the microparticles fundamentally affected metabolism. With 10 g L^-1 talc, S. lividans grew to 40% smaller pellets and, using RNA sequencing, revealed accelerated morphogenesis and aging, indicated by early upregulation of developmental regulator genes such as ssgA, ssgB, wblA, sigN, and bldN. Furthermore, the microparticles re-balanced the expression of individual bottromycin cluster genes, resulting in a higher macrocyclization efficiency at the level of BotAH and correspondingly lower levels of non-cyclized shunt by-products, driving the production of mature bottromycin. Testing a variety of Streptomyces species, talc addition resulted in up to 13-fold higher titers for the RiPPs bottromycin and cinnamycin, the alkaloid undecylprodigiosin, the polyketide pamamycin, the tetracycline-type oxytetracycline, and the anthramycin-analogs usabamycins. Moreover, talc addition boosted production in other actinobacteria, outside of the genus of Streptomyces: vancomycin (Amycolatopsis japonicum DSM 44213), teicoplanin (Actinoplanes teichomyceticus ATCC 31121), and the angucyclinone-type antibiotic simocyclinone (Kitasatospora sp.). For teicoplanin, the microparticles were even crucial to activate production. Taken together, the use of talc was beneficial in 75% of all tested cases and optimized natural and heterologous hosts forming the substance of interest with clusters under native and synthetic control. Given its simplicity and broad benefits, microparticle-supplementation appears as an enabling technology in natural product research of these most important microbes.

Tolerance to Abiotic Factors of Microsclerotia and Mycelial Pellets From Metarhizium robertsii, and Molecular and Ultrastructural Changes During Microsclerotial Differentiation

Metarhizium species fungi are able to produce resistant structures termed microsclerotia, formed by compact and melanized threads of hyphae. These propagules are tolerant to desiccation and produce infective conidia; thus, they are promising candidates to use in biological control programs. In this study, we investigated the tolerance to both ultraviolet B (UV-B) radiation and heat of microsclerotia of Metarhizium robertsii strain ARSEF 2575. We also adapted the liquid medium and culture conditions to obtain mycelial pellets from the same isolate in order to compare these characteristics between both types of propagules. We followed the peroxisome biogenesis and studied the oxidative stress during differentiation from conidia to microsclerotia by transmission electron microscopy after staining with a peroxidase activity marker and by the expression pattern of genes potentially involved in these processes. We found that despite their twice smaller size, microsclerotia exhibited higher dry biomass, yield, and conidial productivity than mycelial pellets, both with and without UV-B and heat stresses. From the 16 genes measured, we found an induction after 96-h differentiation in the oxidative stress marker genes MrcatA, MrcatP, and Mrgpx; the peroxisome biogenesis factors Mrpex5 and Mrpex14/17; and the photoprotection genes Mrlac1 and Mrlac2; and Mrlac3. We concluded that an oxidative stress scenario is induced during microsclerotia differentiation in M. robertsii and confirmed that because of its tolerance to desiccation, heat, and UV-B, this fungal structure could be an excellent candidate for use in biological control of pests under tropical and subtropical climates where heat and UV radiation are detrimental to entomopathogenic fungi survival and persistence.

Accelerated glucose metabolism in hyphae-dispersed Aspergillus oryzae is suitable for biological production

Recently, a hyphae-dispersed type of filamentous fungus Aspergillus oryzae was constructed via genetic engineering, and industrial applications are expected due to the ease of handling and to the level of protein production properties. In this study, we constructed cellulase-expressing strains using wild-type and hyphae-dispersed strains to investigate the correlation between protein productivity and metabolism. Compared with the original strain, the hyphae-dispersed cellulase-expressing strain showed elevated cellulase activity, rapid glucose consumption, increased mycelial dry weight, an increased expression of cellulase genes, and activated respiration activity. Comparative metabolomic analysis showed fewer metabolites in the glycolysis and TCA cycles in the dispersed strains than in the original strains. These results indicate that the flux of carbohydrate metabolism in the hyphae-dispersed strains is smoother than that in the original strains. Such efficient metabolic flux would contribute to efficient energy conversion and to sufficient energy supply to anabolisms, such as mycelial growth and protein production. Our findings suggest that the hyphae-dispersed strains could be a useful host not only for protein production but also for the biological production of various chemicals such as organic acids.

Colors of life: a review on fungal pigments

Colorants find social and commercial applications in cosmetics, food, pharmaceuticals, textiles, and other industrial sectors. Among the available options, chemically synthesized colorants are popular due to their low-cost and flexible production modes, but health and environmental concerns have encouraged the valorization of biopigments that are natural and ecofriendly. Among natural biopigment producers, microorganisms are noteworthy for their all-seasonal production of stable and low-cost pigments with high-yield titers. Fungi are paramount sources of natural pigments. They occupy diverse ecological niches with adaptive metabolisms and biocatalytic pathways, making them entities with an industrial interest. Industrially important biopigments like carotenoids, melanins, riboflavins, azaphilones, and quinones produced by filamentous fungi are described within the context of this review. Most recent information about fungal pigment characteristics, biochemical production routes and pathways, potential applications, limitations, and future research perspectives are described.

Microbioreactor-assisted cultivation workflows for time-efficient phenotyping of protein producing Aspergillus niger in batch and fed-batch mode

In recent years, many fungal genomes have become publicly available. In combination with novel gene editing tools, this allows for accelerated strain construction, making filamentous fungi even more interesting for the production of valuable products. However, besides their extraordinary production and secretion capacities, fungi most often exhibit challenging morphologies, which need to be screened for the best operational window. Thereby, combining genetic diversity with various environmental parameters results in a large parameter space, creating a strong demand for time-efficient phenotyping technologies. Microbioreactor systems, which have been well established for bacterial organisms, enable an increased cultivation throughput via parallelization and miniaturization, as well as enhanced process insight via non-invasive online monitoring. Nevertheless, only few reports about microtiter plate cultivation for filamentous fungi in general and even less with online monitoring exist in literature. Moreover, screening under batch conditions in microscale, when a fed-batch process is performed in large-scale might even lead to the wrong identification of optimized parameters. Therefore, in this study a novel workflow for Aspergillus niger was developed, allowing for up to 48 parallel microbioreactor cultivations in batch as well as fed-batch mode. This workflow was validated against lab-scale bioreactor cultivations to proof scalability. With the optimized cultivation protocol, three different micro-scale fed-batch strategies were tested to identify the best protein production conditions for intracellular model product GFP. Subsequently, the best feeding strategy was again validated in a lab-scale bioreactor.

A fully automated pipeline for the dynamic at-line morphology analysis of microscale Aspergillus cultivation

Background

Morphology, being one of the key factors influencing productivity of filamentous fungi, is of great interest during bioprocess development. With increasing demand of high-throughput phenotyping technologies for fungi due to the emergence of novel time-efficient genetic engineering technologies, workflows for automated liquid handling combined with high-throughput morphology analysis have to be developed.

Results

In this study, a protocol allowing for 48 parallel microbioreactor cultivations of Aspergillus carbonarius with non-invasive online signals of backscatter and dissolved oxygen was established. To handle the increased cultivation throughput, the utilized microbioreactor is integrated into a liquid handling platform. During cultivation of filamentous fungi, cell suspensions result in either viscous broths or form pellets with varying size throughout the process. Therefore, tailor-made liquid handling parameters such as aspiration/dispense height, velocity and mixing steps were optimized and validated. Development and utilization of a novel injection station enabled a workflow, where biomass samples are automatically transferred into a flow through chamber fixed under a light microscope. In combination with an automated image analysis concept, this enabled an automated morphology analysis pipeline. The workflow was tested in a first application study, where the projected biomass area was determined at two different cultivation temperatures and compared to the microbioreactor online signals.

Conclusions

A novel and robust workflow starting from microbioreactor cultivation, automated sample harvest and processing via liquid handling robots up to automated morphology analysis was developed. This protocol enables the determination of projected biomass areas for filamentous fungi in an automated and high-throughput manner. This measurement of morphology can be applied to describe overall pellet size distribution and heterogeneity.

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.

A set of simple methods for detection and extraction of laminarinase

A carefully designed ammonium sulfate precipitation will simplify extraction of proteins and is considered to be a gold standard among various precipitation methods. Therefore, optimization of ammonium sulfate precipitation can be an important functional step in protein purification. The presence of high amounts of ammonium sulphate precludes direct detection of many enzymatically active proteins including reducing sugar assays (e.g. Nelson-Somogyi, Reissig and 3,5-dinitrosalicylic acid methods) for assessing carbohydrases (e.g. laminarinase (β (1-3)-glucanohydrolase), cellulases and chitinases). In this study, a simple method was developed using laminarin infused agarose plate for the direct analysis of the ammonium sulphate precipitates from Streptomyces rimosus AFM-1. The developed method is simple and convenient that can give accurate results even in presence of ammonium sulfate in the crude precipitates. Laminarin is a translucent substrate requiring the use of a stain to visualize the zones of hydrolysis in a plate assay. A very low-cost and locally available fluorescent optical fabric brightener Tinopal CBS-X has been used as a stain to detect the zones of hydrolysis. We also report simple methods to prepare colloidal chitin and cell free supernatant in this manuscript.

Endocrine-disruptive chemicals as contaminants of emerging concern in wastewater and surface water: A review

Population growth followed by rapid development of industrialisation has caused serious environmental pollution with contaminants of emerging concern found in wastewater and surface water. As one of the most important resources for human survival, water is daily polluted by endocrine-disruptive chemicals (EDCs) including pharmaceuticals and personal care products, organic pollutants and heavy metals. Even at low concentrations in water bodies, chronic exposure to EDCs can cause adverse effects on human and environment health. The main concern with EDCs is the diseases they can generate in humans or wildlife by affecting the function of hormones in the body. Problems in the reproductive system, thyroid problems, Alzheimer's, cancer and obesity are some of the major effects of EDCs in humans. In wildlife, the reproductive system may be affected, including its levels of hatchability and vitellogenin. The efforts of the present review are on emphasising on the environmental concern on the occurrence and risk assessment of EDCs, their harmful effects in the ecosystem, human life, and wildlife, as a result of their incomplete removal from wastewater treatment plants. The review focuses on studies conducted in South Africa highlights the use of fungal bioreactors as a low-cost and eco-effective environmentally friendly wastewater treatment processes.

Assimilation of Cholesterol by Monascus purpureus

Monascus purpureus, a filamentous fungus known for its fermentation of red yeast rice, produces the metabolite monacolin K used in statin drugs to inhibit cholesterol biosynthesis. In this study, we show that active cultures of M. purpureus CBS 109.07, independent of secondary metabolites, use the mechanism of cholesterol assimilation to lower cholesterol in vitro. We describe collection, extraction, and gas chromatography-flame ionized detection (GC-FID) methods to quantify the levels of cholesterol remaining after incubation of M. purpureus CBS 109.07 with exogenous cholesterol. Our findings demonstrate that active growing M. purpureus CBS 109.07 can assimilate cholesterol, removing 36.38% of cholesterol after 48 h of incubation at 37 °C. The removal of cholesterol by resting or dead M. purpureus CBS 109.07 was not significant, with cholesterol reduction ranging from 2.75-9.27% throughout a 72 h incubation. Cholesterol was also not shown to be catabolized as a carbon source. Resting cultures transferred from buffer to growth media were able to reactivate, and increases in cholesterol assimilation and growth were observed. In growing and resting phases at 24 and 72 h, the production of the mycotoxin citrinin was quantified via high-performance liquid chromatography-ultraviolet (HPLC-UV) and found to be below the limit of detection. The results indicate that M. purpureus CBS 109.07 can reduce cholesterol content in vitro and may have a potential application in probiotics.

Universal law for diffusive mass transport through mycelial networks

Filamentous fungal cell factories play a pivotal role in biotechnology and circular economy. Hyphal growth and macroscopic morphology are critical for product titers; however, these are difficult to control and predict. Usually pellets, which are dense networks of branched hyphae, are formed during industrial cultivations. They are nutrient- and oxygen-depleted in their core due to limited diffusive mass transport, which compromises productivity of bioprocesses. Here, we demonstrate that a generalized law for diffusive mass transport exists for filamentous fungal pellets. Diffusion computations were conducted based on three-dimensional X-ray microtomography measurements of 66 pellets originating from four industrially exploited filamentous fungi and based on 3125 Monte Carlo simulated pellets. Our data show that the diffusion hindrance factor follows a scaling law with respect to the solid hyphal fraction. This law can be harnessed to predict diffusion of nutrients, oxygen, and secreted metabolites in any filamentous pellets and will thus advance the rational design of pellet morphologies on genetic and process levels.

Microbial Colorants Production in Stirred-Tank Bioreactor and Their Incorporation in an Alternative Food Packaging Biomaterial

Natural colorants from microbial fermentation have gained significant attention in the market to replace the synthetic ones. Talaromyces spp. produce yellow-orange-red colorants, appearing as a potential microorganism to be used for this purpose. In this work, the production of natural colorants by T. amestolkiae in a stirred-tank bioreactor is studied, followed by its application as additives in bio-based films. The effect of the pH-shift control strategy from 4.5 to 8.0 after 96 h of cultivation is evaluated at 500 rpm, resulting in an improvement of natural colorant production, with this increase being more significant for the orange and red ones, both close to 4-fold. Next, the fermented broth containing the colorants is applied to the preparation of cassava starch-based films in order to incorporate functional activity in biodegradable films for food packaging. The presence of fermented broth did not affect the water activity and total solids of biodegradable films as compared with the standard one. In the end, the films are used to pack butter samples (for 45 days) showing excellent results regarding antioxidant activity. It is demonstrated that the presence of natural colorants is obtained by a biotechnology process, which can provide protection against oxidative action, as well as be a functional food additive in food packing biomaterials.

Exploring the extremes: applying high concentration of yeast extract leads to drastic morphological changes and elimination of (+)-geodin and asterric acid production in Aspergillus terreus submerged cultures

Objective

Evaluation of morphology and secondary metabolites production in Aspergillus terreus ATCC 20542 cultures over a wide range of lactose and yeast extract concentrations from 0.2 up to an extremely high level of 200 g l^−l.

Results

The morphological differences of mycelial objects were quantified with the use of morphological parameters calculated by applying the tools of digital image analysis. At 200 g l^−l of yeast extract clumps and loose hyphae were recorded instead of pellets commonly observed in submerged cultures of A. terreus. Under these conditions the biosynthesis of (+)-geodin and asterric acid was totally blocked, lovastatin formation was found to be at a relatively low level and biomass production turned out to be greater than in the remaining variants, where the pelleted growth was observed. At 200 g l^−l of lactose the production of lovastatin, (+)-geodin and asterric acid was visibly stimulated compared to the media containing 0.2, 2 and 20 g l^−l of the sugar substrate, but at the same time no traces of butyrolactone I could be detected in the broth. Lactose at the extremely high concentration of 200 g l^−l did not induce the drastic morphological changes observed in the case of 200 g l^-1 of yeast extract. It was proved that at the C/N values as low as 4 and as high as 374 A. terreus not only continued to display growth but also exhibited the production of secondary metabolites. The use of cultivation media representing the equivalent C/N ratios led to different metabolic and morphological outcomes depending on the concentration of lactose and yeast extract that contributed to the given C/N value.

Conclusion

The extremely high concentration of yeast extract leads to marked morphological changes of A. terreus and the elimination of (+)-geodin and asterric production, while applying the excess of lactose is stimulatory in terms of lovastatin production.

Electronic supplementry material

The online version of this article (10.1007/s10529-020-03018-5) contains supplementary material, which is available to authorized users.

Recovering Secondary REE Value from Spent Oil Refinery Catalysts Using Biogenic Organic Acids

Spent catalysts produced by oil refinery industries are regarded as an important secondary source for valuable metals. In particular, spent fluid catalytic cracking (FCC) catalysts represent a potential source for rare earth elements (REEs). This study aimed to exploit the leachability of spent FCC catalysts as a secondary source for La, by using an alternative organic acid lixiviant produced under optimized fungal fermentation conditions. The first chemical leaching tests revealed that citric acid (>100 mM) is a comparable alternative lixiviant to conventional inorganic acids (1 M) and that the La dissolution behavior changed significantly with different types of organic acids. The initial fungal fermentation conditions (e.g., inoculum level, substrate concentration, pH) largely affected the resultant biogenic acid composition, and its manipulation was possible in order to almost solely ferment citric acid (~130 mM) while controlling the production of unwanted oxalic acid. The performance of actual biogenic acids (direct use of cell-free spent media) and artificially reconstituted biogenic acids (a mixture of chemical reagents) was nearly identical, achieving a final La dissolution of ~74% at a pulp density of 5%. Overall, the microbiological fermentation of organic acids could become a promising approach to supply an efficient and environmentally benign alternative lixiviant for REE scavenging from spent FCC catalyst wastes.

Towards a better understanding of microalgae natural flocculation mechanisms to enhance flotation harvesting efficiency

In microalgae harvesting, flocculation is usually a compulsory preliminary step to further separation by sedimentation or flotation. For some microalgae species, and under certain growth conditions, flocculation can occur naturally. Natural flocculation presents many advantages as it does not require the addition of any flocculants to the culture medium and shows high efficiency rate. But because natural flocculation is so specific to the species and conditions, and thanks to the knowledge accumulated over the last years on flocculation mechanisms, researchers have developed strategies to induce this natural harvesting. In this review, we first decipher at the molecular scale the underlying mechanisms of natural flocculation and illustrate them by selected studies from the literature. Then we describe the developed strategies to induce natural flocculation that include the use of biopolymers, chemically modified or not, or involve mixed species cultures. But all these strategies need the addition of external compounds or microorganism which can present some issues. Thus alternative directions to completely eliminate the need for an external molecule, through genetic engineering of microalgae strains, are presented and discussed in the third part of this review.

High throughput, small scale methods to characterise the growth of marine fungi

Various marine fungi have been shown to produce interesting, bioactive compounds, but scaling up the production of these compounds can be challenging, particularly because little is generally known about how the producing organisms grow. Here we assessed the suitability of using 100-well BioScreen plates or 96-well plates incubated in a robot hotel to cultivate eight filamentous marine fungi, six sporulating and two non-sporulating, to obtain data on growth and substrate (glucose, xylose, galactose or glycerol) utilisation in a high throughput manner. All eight fungi grew in both cultivation systems, but growth was more variable and with more noise in the data in the Cytomat plate hotel than in the BioScreen. Specific growth rates between 0.01 (no added substrate) and 0.07 h^-1 were measured for strains growing in the BioScreen and between 0.01 and 0.27 h^-1 for strains in the plate hotel. Three strains, Dendryphiella salina LF304, Penicillium chrysogenum KF657 and Penicillium pinophilum LF458, consistently had higher specific growth rates on glucose and xylose in the plate hotel than in the BioScreen, but otherwise results were similar in the two systems. However, because of the noise in data from the plate hotel, the data obtained from it could only be used to distinguish between substrates which did or did not support growth, whereas data from BioScreen also provided information on substrate preference. Glucose was the preferred substrate for all strains, followed by xylose and galactose. Five strains also grew on glycerol. Therefore it was important to minimise the amount of glycerol introduced with the inoculum to avoid misinterpreting the results for growth on poor substrates. We concluded that both systems could provide physiological data with filamentous fungi, provided sufficient replicates are included in the measurements.

Quantitative Proteome Profiling Reveals Cellobiose-Dependent Protein Processing and Export Pathways for the Lignocellulolytic Response in Neurospora crassa

Filamentous fungi are intensively used for producing industrial enzymes, including lignocellulases. Employing insoluble cellulose to induce the production of lignocellulases causes some drawbacks, e.g., a complex fermentation operation, which can be overcome by using soluble inducers such as cellobiose. Here, a triple β-glucosidase mutant of Neurospora crassa, which prevents rapid turnover of cellobiose and thus allows the disaccharide to induce lignocellulases, was applied to profile the proteome responses to cellobiose and cellulose (Avicel). Our results revealed a shared proteomic response to cellobiose and Avicel, whose elements included lignocellulases and cellulolytic product transporters. While the cellulolytic proteins showed a correlated increase in protein and mRNA levels, only a moderate correlation was observed on a proteomic scale between protein and mRNA levels (R ² = 0.31). Ribosome biogenesis and rRNA processing were significantly overrepresented in the protein set with increased protein but unchanged mRNA abundances in response to Avicel. Ribosome biogenesis, as well as protein processing and protein export, was also enriched in the protein set that showed increased abundance in response to cellobiose. NCU05895, a homolog of yeast CWH43, is potentially involved in transferring a glycosylphosphatidylinositol (GPI) anchor to nascent proteins. This protein showed increased abundance but no significant change in mRNA levels. Disruption of CWH43 resulted in a significant decrease in cellulase activities and secreted protein levels in cultures grown on Avicel, suggesting a positive regulatory role for CWH43 in cellulase production. The findings should have an impact on a systems engineering approach for strain improvement for the production of lignocellulases.IMPORTANCE Lignocellulases are important industrial enzymes for sustainable production of biofuels and bio-products. Insoluble cellulose has been commonly used to induce the production of lignocellulases in filamentous fungi, which causes a difficult fermentation operation and enzyme loss due to adsorption to cellulose. The disadvantages can be overcome by using soluble inducers, such as the disaccharide cellobiose. Quantitative proteome profiling of the model filamentous fungus Neurospora crassa revealed cellobiose-dependent pathways for cellulase production, including protein processing and export. A protein (CWH43) potentially involved in protein processing was found to be a positive regulator of lignocellulase production. The cellobiose-dependent mechanisms provide new opportunities to improve the production of lignocellulases in filamentous fungi.

The mechanisms of hyphal pellet formation mediated by polysaccharides, α-1,3-glucan and galactosaminogalactan, in Aspergillus species

Filamentous fungi are widely used for production of enzymes and chemicals, and are industrially cultivated both in liquid and solid cultures. Submerged culture is often used as liquid culture for filamentous fungi. In submerged culture, filamentous fungi show diverse macromorphology such as hyphal pellets and dispersed hyphae depending on culture conditions and genetic backgrounds of fungal strains. Although the macromorphology greatly affects the productivity of submerged cultures, the specific cellular components needed for hyphal aggregation after conidial germination have not been characterized. Recently we reported that the primary cell wall polysaccharide α-1,3-glucan and the extracellular polysaccharide galactosaminogalactan (GAG) contribute to hyphal aggregation in Aspergillus oryzae, and that a strain deficient in both α-1,3-glucan and GAG shows dispersed hyphae in liquid culture. In this review, we summarize our current understanding of the contribution of chemical properties of α-1,3-glucan and GAG to hyphal aggregation. Various ascomycetes and basidiomycetes have α-1,3-glucan synthase gene(s). In addition, some Pezizomycotina fungi, including species used in the fermentation industry, also have GAG biosynthetic genes. We also review here the known mechanisms of biosynthesis of α-1,3-glucan and GAG. Regulation of the biosynthesis of the two polysaccharides could be a potential way of controlling formation of hyphal pellets.

Disruption and overexpression of 6-phosphofructo-2-kinase influence organic acid production in Aspergillus carbonarius ITEM 5010

Aspergillus carbonarius is an efficient producer of organic acids with great potential for bio-based production of organic acids. In this study, we identified a gene f2kp encoding the enzyme 6-phosphofructo-2-kinase known as an allosteric regulator of the glycolytic flux and investigated its role in the production of organic acid. The strategy was to examine the impact of citric acid and malic acid production by overexpressing and disrupting f2kp, respectively. The overexpressing transformants expressed f2kp at higher level than the wild type, whereas no expression of f2kp was detected in the knockout transformants. Citric acid and malic acid production by the knockout strains decreased sharply along with a significant lower sugar consumption, though the overexpressing transformants produced similar amounts of citric acid and malic acid as the wild type. We conclude that 6-phosphofructo-2-kinase has an important regulatory role for the glycolytic flux and organic acid production in A. carbonarius.

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.

Three-dimensional cellular aggregates formed by Beauveria pseudobassiana in liquid culture with potential for use as a biocontrol agent of the African black beetle (Heteronychus arator)

Beauveria pseudobassiana formed three-dimensional aggregates of cells (CAs) in liquid culture. CAs were formed mainly by blastospores and conidia, distinct from microsclerotia formed through adhesion of hyphae. The formation, germination and sporulation of CAs were studied, as well as the pathogenicity of conidia produced from them against adults of black beetle. After 4 days of culture, CAs were formed, becoming compact and melanised after 10 days of incubation. Electron microscopy showed three-dimensional CAs averaging 431.65 µm in length with irregular shapes and rough surfaces, where cells were trapped within an extracellular matrix. CAs germinated after 2 days of incubation on agar-plates producing hyphae and forming phialides and conidia after 4 days. Produced conidia caused 45% mortality of black beetle adults. CAs germination and sporulation on soil were directly correlated with soil moisture, reaching 80% and 100% germination on the surface of soil with 17% and 30% moisture, respectively. CAs maintained 100% germination after 2 years of storage under refrigeration. These CAs could have a similar function as microsclerotia in nature, acting as resistant structures able to protect internal cells and their ability to sporulate producing infective conidia, suggesting their potential to be used as bioinsecticides to control soil-dwelling insects.

Comparative evaluation of Aspergillus niger strains for endogenous pectin-depolymerization capacity and suitability for D-galacturonic acid production

Pectinaceous agricultural residues rich in D-galacturonic acid (D-GalA), such as sugar beet pulp, are considered as promising feedstocks for waste-to-value conversions. Aspergillus niger is known for its strong pectinolytic activity. However, while specialized strains for production of citric acid or proteins are well characterized, this is not the case for the production of pectinases. We, therefore, systematically compared the pectinolytic capabilities of six A. niger strains (ATCC 1015, ATCC 11414, NRRL 3122, CBS 513.88, NRRL 3, and N402) using controlled batch cultivations in stirred-tank bioreactors. A. niger ATCC 11414 showed the highest polygalacturonase activity, specific protein secretion, and a suitable morphology. Furthermore, D-GalA release from sugar beet pulp was 75% higher compared to the standard lab strain A. niger N402. Our study, therefore, presents a robust initial strain selection to guide future process improvement of D-GalA production from agricultural residues and identifies a high-performance base strain for further genetic optimizations.

A Chemometric Tool to Monitor and Predict Cell Viability in Filamentous Fungi Bioprocesses Using UV Chromatogram Fingerprints

Monitoring process variables in bioprocesses with complex expression systems, such as filamentous fungi, requires a vast number of offline methods or sophisticated inline sensors. In this respect, cell viability is a crucial process variable determining the overall process performance. Thus, fast and precise tools for identification of key process deviations or transitions are needed. However, such reliable monitoring tools are still scarce to date or require sophisticated equipment. In this study, we used the commonly available size exclusion chromatography (SEC) HPLC technique to capture impurity release information in Penicillium chrysogenum bioprocesses. We exploited the impurity release information contained in UV chromatograms as fingerprints for development of principal component analysis (PCA) models to descriptively analyze the process trends. Prediction models using well established approaches, such as partial least squares (PLS), orthogonal PLS (OPLS) and principal component regression (PCR), were made to predict the viability with model accuracies of 90% or higher. Furthermore, we demonstrated the platform applicability of our method by monitoring viability in a Trichoderma reesei process for cellulase production. We are convinced that this method will not only facilitate monitoring viability of complex bioprocesses but could also be used for enhanced process control with hybrid models in the future.

From field sampling to pneumatic bioreactor mycelia production of the ectomycorrhizal mushroom Laccaria trichodermophora

In order to increase survival rates of greenhouse seedlings destined for restoration and conservation programs, successful mycorrhization of the seedlings is necessary. To reforest forest ecosystems, host trees must be inoculated with ectomycorrhizal fungi and, in order to guarantee a sufficient supply of ectomycorrhizal inoculum, it is necessary to develop technologies for the mass production of ectomycorrhizal fungi mycelia. We selected the ectomycorrhizal fungus Laccaria trichodermophora, due to its ecological traits and feasible mycelia production in asymbiotic conditions. Here, we report the field sampling of genetic resources, as well as the highly productive nutritional media and cultivation parameters in solid cultures. Furthermore, in order to achieve high mycelial production, we used strain screening and evaluated pH, carbon source concentration, and culture conditions of submerged cultures in normal and baffled shake flasks. The higher productivity culture conditions in shake flasks were selected for evaluation in a pneumatic bioreactor, using modified BAF media with a 10 g/L glucose, pH 5.5, 25 °C, and a volumetric oxygen transfer coefficient (K_La) of 36 h^-1. Under those conditions less biomass (12-37 %) was produced in the pneumatic bioreactor compared with the baffled shake flasks. This approach shows that L. trichodermophora can generate a large biomass concentration and constitute the biotechnological foundation of its mycelia mass production.

Current views on endocytosis in filamentous fungi

Filamentous fungi grow by adding cell wall and membrane exclusively at the apex of tubular structures called hyphae. Growth was previously believed to occur only through exocytosis at the Spitzenkörper, an organised body of secretory macro- and microvesicles found only in growing hyphae. More recent work has indicated that an area deemed the sub-apical collar is enriched for endocytosis and is also required for hyphal growth. It is now generally believed that polarity of filamentous fungi is achieved through the balancing of the processes of endocytosis and exocytosis at these two areas. This review is an update on the current progress and understanding surrounding the occurrence of endocytosis and its spatial regulation as they pertain to growth and pathogenicity in filamentous fungi.

Biotransformation of struvite by Aspergillus niger: phosphate release and magnesium biomineralization as glushinskite

Struvite (magnesium ammonium phosphate-MgNH₄ PO₄ ·6H₂ O), which can extensively crystallize in wastewater treatments, is a potential source of N and P as fertilizer, as well as a means of P conservation. However, little is known of microbial interactions with struvite which would result in element release. In this work, the geoactive fungus Aspergillus niger was investigated for struvite transformation on solid and in liquid media. Aspergillus niger was capable of solubilizing natural (fragments and powder) and synthetic struvite when incorporated into solid medium, with accompanying acidification of the media, and extensive precipitation of magnesium oxalate dihydrate (glushinskite, Mg(C₂ O₄ ).2H₂ O) occurring under growing colonies. In liquid media, A. niger was able to solubilize natural and synthetic struvite releasing mobile phosphate (PO₄ ^3- ) and magnesium (Mg²⁺ ), the latter reacting with excreted oxalate resulting in precipitation of magnesium oxalate dihydrate which also accumulated within the mycelial pellets. Struvite was also found to influence the morphology of A. niger mycelial pellets. These findings contribute further understanding of struvite solubilization, element release and secondary oxalate formation, relevant to the biogeochemical cycling of phosphate minerals, and further directions utilizing these mechanisms in environmental biotechnologies such as element biorecovery and biofertilizer applications.