Morphology and productivity of filamentous fungi

Morphology and laccase production of white-rot fungi grown on wheat bran flakes under semi-solid-state fermentation conditions

In this paper, we studied the laccase production and the growth morphology of different white-rot fungi, i.e. Pleurotus ostreatus, Trametes pubescens, Cerrena unicolor and Trametes versicolor, cultured under semi-solid-state fermentation conditions using wheat bran flakes as a natural low-cost support substrate. Trametes versicolor exhibited the highest laccase activity per gram of total dry matter, followed by P. ostreatus (63.5 and 58.2Ug(-1) , respectively). In addition, they showed a time profile of laccase production that was quite similar. Growth morphology was studied using environmental microscopic images and analyzed by discrete Fourier transformation-based software to determine the mean diameter of the hyphae, the number of hypha layers and the global micromorphology. The four strains exhibited different micromorphologies of growth. Pleurotus ostreatus presented narrow hyphae, which formed many thick clumps, T. pubescens and T. versicolor showed clumps of different sizes and C. unicolor showed thick hyphae that formed larger clumps, but in less amounts.

Aspergillus as a multi-purpose cell factory: current status and perspectives

Aspergilli have a long history in biotechnology as expression platforms for the production of food ingredients, pharmaceuticals and enzymes. The achievements made during the last years, however, have the potential to revolutionize Aspergillus biotechnology and to assure Aspergillus a dominant place among microbial cell factories. This mini-review will highlight most recent breakthroughs in fundamental and applied Aspergillus research with a focus on new molecular tools, techniques and products. New trends and concepts related to Aspergillus genomics and systems biology will be discussed as well as the challenges that have to be met to integrate omics data with metabolic engineering attempts.

Disposable parallel poly(dimethylsiloxane) microbioreactor with integrated readout grid for germination screening of Aspergillus ochraceus

In this work a disposable, parallel microbioreactor (MBR) suitable for screening in batch or continuous mode is presented. The reactor consists of five parallel microchambers made of poly(dimethylsiloxane) bonded to a glass substrate. A grid structure is engraved on each chamber, allowing subsequent morphology imaging. Measurements are recorded over the entire cultivation period with constant parameters, namely, position and focus in the z-axis. The microdevice may be used for either parallel, uni- or multiparametric screening, and overcomes the drawback of gridless microwell plates which require expensive equipment such as an inverted microscope with an automatic stage. To validate the scalability from laboratory scale to microscale, and thus the cultivation protocol in the MBR, the germination of fungal spores (A. ochraceus) is evaluated for two different key magnitudes (pH and temperature) and compared to the results obtained from conventional laboratory scale systems (flasks and agar plates). Information on germination capacity with regard to interspecies' variability allows for optimization of industrial processes as optimal pH and temperature matched to the mesoscopic cultivation systems. The germination conditions therefore remain unaffected inside the MBR, while providing the following advantages: (i) dramatic reduction of medium consumption, (ii) submerged cultivation with constant oxygen supply, (iii) assured low cost and disposability, and (iv) possibility of a continuous cultivation mode.

Differentiation of Acremonium chrysogenum M35 in submerged culture with glass beads or silicone rubbers

In this study, we investigated the effects of glass beads and silicone rubbers on the differentiation and morphological changes of A. chrysogenum M35 in submerged culture. Differentiation in the center of the cell pellets was improved by the addition of glass beads or silicone rubbers to the primary medium. The fragmentation rate constant (k(frag)), which is used to estimate the tensile strength of fungal hyphae, was increased by more than 40% in baffled flasks containing glass beads. The maximum fragmentation rate was also increased by 48% when silicone rubbers were added to a 5 L bioreactor containing the culture. During the cultivation in the main medium with 6 glass beads, the value of the fractal dimension increased by about 8% when it was compared with baffled flasks without glass beads. Additionally, the number of arthrospores and the dry cell weight were increased by more than 10% in baffled flasks containing beads. The degree of roundness, which is the ratio of the object area to the longest Feret diameter, was decreased from 0.85 at day 1 to 0.77 at day 5. The differentiation of A. chrysogenum M35 was also supposedly closely related with the enlargement of the cell surfaces. Taken together, these results indicate that complex changes in morphology resulted in increased cell growth and differentiation in the culture broth containing glass beads and silicone rubbers.

Monoclonal antibodies against peptidorhamnomannans of Scedosporium apiospermum enhance the pathogenicity of the fungus

Scedosporium apiospermum is part of the Pseudallescheria-Scedosporium complex. Peptidorhamnomannans (PRMs) are cell wall glycopeptides present in some fungi, and their structures have been characterized in S. apiospermum, S. prolificans and Sporothrix schenckii. Prior work shows that PRMs can interact with host cells and that the glycopeptides are antigenic. In the present study, three monoclonal antibodies (mAbs, IgG1) to S. apiospermum derived PRM were generated and their effects on S. apiospermum were examined in vitro and in vivo. The mAbs recognized a carbohydrate epitope on PRM. In culture, addition of the PRM mAbs increased S. apiospermum conidia germination and reduced conidial phagocytosis by J774.16 macrophages. In a murine infection model, mice treated with antibodies to PRM died prior to control animals. Thus, PRM is involved in morphogenesis and the binding of this glycopeptide by mAbs enhanced the virulence of the fungus. Further insights into the effects of these glycopeptides on the pathobiology of S. apiospermum may lead to new avenues for preventing and treating scedosporiosis.

The incidence of fungal infections has increased dramatically over the last 50 years, largely because of the increasing size of the population at risk, which especially includes immunocompromised hosts. Scedosporium apiospermum is a filamentous fungus that causes a variety of infections, ranging from localized disease to life-threatening disseminated infections. Glycoproteins are molecules present in the fungal surface and are comprised of carbohydrate and protein components. They are involved in different important functions in the fungal cell. Monoclonal antibodies can be used as therapeutic agents for infectious disease, but some factors involved in their efficacy are often not well understood. We found that monoclonal antibodies to glycoproteins present in fungal surface can be nonprotective and can even enhance the disease. The administration of these antibodies can affect functions of the fungal cell and the immune cells, resulting in a survival advantage for the fungus during interactions with the host.

Determination of adhesion between single Aspergillus niger spores in aqueous solutions using an atomic force microscope

The interaction force between single cells in contact is of high interest in various interdisciplinary fields of biotechnology, for instance, in cultivation or biofilm formation. A method for the determination of adhesion forces between two single Aspergillus niger spores in different aqueous solutions was established in this study. Adhesion force distributions were determined at three different sodium chloride concentrations and two different pH values using an atomic force microscope (AFM). It was pointed out that adhesion data can be described by log-normal density functions, of which corresponding parameters have been estimated. Using the knowledge of distribution shape, the influence of the environmental condition on the mean values of adhesion force could be studied quantitatively. The highest value of 0.95 nN was observed at pH 2.5 and an ionic strength of 0.5 mol L(-1). Decreasing the ionic strength to 0.05 mol L(-1) decreases the adhesion force mean for about 25%. Increasing the pH value to pH 5 at a sodium chloride concentration of 0.154 mol L(-1) entails a decrease of adhesion from 0.88 to 0.56 nN. These results qualitatively agree with the absolute value of the expected surface potential of Aspergillus niger spores, which is much higher at pH 5 and should take more effect at lower concentrations of counterions.

Effect of environmental conditions on extracellular lipases production and fungal morphology from Aspergillus niger MYA 135

Under the current assay conditions, lipase production in mineral medium was only detected in the presence of vegetable oils, reaching the highest specific activity with olive oil. In this way, effect of different environmental conditions on fungal morphology and olive oil-induced extracellular lipases production from Aspergillus niger MYA 135 was studied. It was observed that addition of 1.0 g l(-1) FeCl(3)to the medium encouraged filamentous growth and increased the specific activity 6.6 fold after 4 days of incubation compared to the control. However, major novelty of this study was the satisfactory production of an acidic lipase at initial pH 3 of the culture medium (1.74 +/- 0.06 mU microg(-1)), since its potencial applications in food and pharmaceutical industry are highly promising.

Structural analysis of biofilms and pellets of Aspergillus niger by confocal laser scanning microscopy and cryo scanning electron microscopy

Biomass organization of Aspergillus niger biofilms and pellets stained with fluorescein isothiocyanate were analyzed by means of confocal laser scanning microscopy and detectable differences between both types of growth were found. Three-dimensional surface plot analysis of biofilm structure revealed interstitial voids and vertical growth compared with pellets. Growth was lower in biofilm and according to fluorescence profile obtained, biomass density increased at the surface (0-20 microm). However, a decrease in fluorescence intensity was observed through optical sections of pellets even though growth was significantly higher than biofilms. Cryo scanning electron microscopy also showed structural differences. While biofilms showed a spatially ordered mycelium and well structured hyphal channels, pellets were characterized by an entangled and notoriously compacted mycelium. These findings revealed common structural characteristics between A. niger biofilms and those found in other microbial biofilms. Thus, biofilm microstructure may represent a key determinant of biofilm growth and physiology of filamentous fungi.

Morphology of filamentous fungi: linking cellular biology to process engineering using Aspergillus niger

In various biotechnological processes, filamentous fungi, e.g. Aspergillus niger, are widely applied for the production of high value-added products due to their secretion efficiency. There is, however, a tangled relationship between the morphology of these microorganisms, the transport phenomena and the related productivity. The morphological characteristics vary between freely dispersed mycelia and distinct pellets of aggregated biomass. Hence, advantages and disadvantages for mycel or pellet cultivation have to be balanced out carefully. Due to this inadequate understanding of morphogenesis of filamentous microorganisms, fungal morphology, along with reproducibility of inocula of the same quality, is often a bottleneck of productivity in industrial production. To obtain an optimisation of the production process it is of great importance to gain a better understanding of the molecular and cell biology of these microorganisms as well as the approaches in biochemical engineering and particle technique, in particular to characterise the interactions between the growth conditions, cell morphology, spore-hyphae-interactions and product formation. Advances in particle and image analysis techniques as well as micromechanical devices and their applications to fungal cultivations have made available quantitative morphological data on filamentous cells. This chapter provides the ambitious aspects of this line of action, focussing on the control and characterisation of the morphology, the transport gradients and the approaches to understand the metabolism of filamentous fungi. Based on these data, bottlenecks in the morphogenesis of A. niger within the complex production pathways from gene to product should be identified and this may improve the production yield.

Molecular basis of and interference into degenerative processes in fungi: potential relevance for improving biotechnological performance of microorganisms

Biological systems, from simple microorganisms to humans, are characterized by time-dependent degenerative processes which lead to reduced fitness, disabilities, severe diseases, and, finally, death. These processes are under genetic control but also influenced by environmental conditions and by stochastic processes. Studying the mechanistic basis of degenerative processes in the filamentous ascomycete Podospora anserina and in other systems demonstrated that mitochondria play a key role in the expression of degenerative phenotypes and unraveled a number of underlying molecular pathways. Reactive oxygen species (ROS) which are mainly, but not exclusively, formed at the mitochondrial respiratory chain are crucial players in this network. While being essential for signaling processes and development, ROS are, at the same time, a potential danger because they lead to molecular damage and degeneration. Fortunately, a number of interacting pathways including ROS scavenging, DNA and protein repair, protein degradation, and mitochondrial fission and fusion are involved in keeping cellular damage low. If these pathways are overwhelmed by extensive damage, programmed cell death is induced. The current knowledge of this hierarchical system of mitochondrial quality control, although still incomplete, appears now to be ready for the development of strategies effective in interventions into those pathways leading to degeneration and loss of performance also in microorganisms used in biotechnology. Very promising interdisciplinary interactions and collaborations involving academic and industrial research teams can be envisioned to arise which bear a great potential, in particular, when system biology approaches are used to understand relevant networks of pathways in a holistic way.

Reconstruction of signaling networks regulating fungal morphogenesis by transcriptomics

Coordinated control of hyphal elongation and branching is essential for sustaining mycelial growth of filamentous fungi. In order to study the molecular machinery ensuring polarity control in the industrial fungus Aspergillus niger, we took advantage of the temperature-sensitive (ts) apical-branching ramosa-1 mutant. We show here that this strain serves as an excellent model system to study critical steps of polar growth control during mycelial development and report for the first time a transcriptomic fingerprint of apical branching for a filamentous fungus. This fingerprint indicates that several signal transduction pathways, including TORC2, phospholipid, calcium, and cell wall integrity signaling, concertedly act to control apical branching. We furthermore identified the genetic locus affected in the ramosa-1 mutant by complementation of the ts phenotype. Sequence analyses demonstrated that a single amino acid exchange in the RmsA protein is responsible for induced apical branching of the ramosa-1 mutant. Deletion experiments showed that the corresponding rmsA gene is essential for the growth of A. niger, and complementation analyses with Saccharomyces cerevisiae evidenced that RmsA serves as a functional equivalent of the TORC2 component Avo1p. TORC2 signaling is required for actin polarization and cell wall integrity in S. cerevisiae. Congruently, our microscopic investigations showed that polarized actin organization and chitin deposition are disturbed in the ramosa-1 mutant. The integration of the transcriptomic, genetic, and phenotypic data obtained in this study allowed us to reconstruct a model for cellular events involved in apical branching.

Potential of Penicillium species in the bioremediation field

The effects on the environment of pollution, particularly that caused by various industrial activities, have been responsible for the accelerated fluxes of organic and inorganic matter in the ecosphere. Xenobiotics such as phenol, phenolic compounds, polycyclic aromatic hydrocarbons (PAHs), and heavy metals, even at low concentrations, can be toxic to humans and other forms of life. Many of the remediation technologies currently being used for contaminated soil and water involve not only physical and chemical treatment, but also biological processes, where microbial activity is the responsible for pollutant removal and/or recovery. Fungi are present in aquatic sediments, terrestrial habitats and water surfaces and play a significant part in natural remediation of metal and aromatic compounds. Fungi also have advantages over bacteria since fungal hyphae can penetrate contaminated soil, reaching not only heavy metals but also xenobiotic compounds. Despite of the abundance of such fungi in wastes, penicillia in particular have received little attention in bioremediation and biodegradation studies. Additionally, several studies conducted with different strains of imperfecti fungi, Penicillium spp. have demonstrated their ability to degrade different xenobiotic compounds with low co-substrate requirements, and could be potentially interesting for the development of economically feasible processes for pollutant transformation.

Disruption of the NADPH-dependent glutamate dehydrogenase affects the morphology of two industrial strains of Penicillium chrysogenum

New morphological aspects of Penicillium chrysogenum were found during physiological characterisation of two NADPH-dependent glutamate dehydrogenase mutant strains. A morphological characterisation of the previously constructed strains, together with the two beta-lactam producing industrial recipient strains, was conducted. The reference strains showed a compact structure with highly branched hyphal elements whereas the morphology of the DeltagdhA strains consisting of long elongated hyphal elements with few branches. On solid medium, the hyphal growth unit (length) increased from an average of 47 microm tip(-1) in the reference strains to 117 microm tip(-1) in the DeltagdhA strains and in submerged cultures a decrease of 18% in branching frequency was measured due to the gdhA deletion. P. chrysogenum Wis 54-1255, the ancestor of most production strains was also characterised and this strain showed morphology similar to the industrial strains. Interestingly, the constructed strains showed morphology similar to wild type Aspergillus nidulans another species carrying the penicillin biosynthetic cluster. Thus, the results showed that elimination of glutamate dehydrogenase activity in high producing strains of P. chrysogenum has a radical impact on morphology.

Pilot-scale process development and scale up for antifungal production

A pilot-scale fermentation was developed for an antifungal compound produced by a filamentous fungus. Replacement of galactose with lactose (20-fold cost savings) and a threefold phosphate reduction (15 to 5 g/L) improved productivity 2.5-fold. Addition of supplements--glycine, cobalt chloride, and trace elements--resulted in a further twofold productivity increase, greater process robustness, and less foaming which reduced antifoam addition tenfold (30 to <3 mL/L). Mid-cycle lactose limitations were addressed by raising initial lactose levels (40 to 120 g/L) resulting in another twofold productivity increase. Overall, peak titers increased tenfold from 45 +/- 9 to 448 +/- 39 mg/L, and productivities improved from 3 to 25 mg/L day. Despite its high productivity, process scale up was challenged by high broth viscosity (5,000-6,000 cP at 16.8 s(-1)). Gassed power requirements at the 600 L scale (4.7 kW/1,000 L) exceeded available power at the 15,000 L scale (3.0 kW/1,000 L), and broth transfer to the downstream isolation facility was hindered. Mid-cycle broth dilution with up to five 10 vol% additions of 12 wt% lactose solution or whole medium-reduced viscosity three- to fivefold (1,000-1,500 cP at 16.8 s(-1)), gassed power within scale-up limits (2.5 kW/1,000 L), and peak titer by up to 45%. The process was scaled up to the 15,000 L working volume based on constant aeration rate (vvm) and peak impeller tip speed, raising superficial velocities at similar shear. This strategy maximized mass transfer rates at target gassed power per unit volume levels, and along with controlled broth viscosity, precluded multiple dilution additions. A final titer of 333 mg/L with one dilution addition was achieved, somewhat lower than expected, likely owing to inhibition from some unmeasured volatile compound (not believed to be carbon dioxide) during an extended period of high back-pressure in the early production phase.

Changes in morphology of Rhizopus chinensis in submerged fermentation and their effect on production of mycelium-bound lipase

In order to control suitable mycelium morphology to obtain high lipase productivity by Rhizopus chinensis in submerged fermentation, the effects of fungal morphology on the lipase production by this strain both in shake flask and fermentor were investigated. Different inoculum level and shear stress were used to develop distinctive morphologies. Analyses and investigations both on micromorphology and macromorphology were performed. Study of micromorphology reveals that micromorphologies for dispersed mycelia and aggregated mycelia are different in cell shape, biosynthetic activity. Macromorphology and broth rheology study in fermentor indicate that pellet formation results in low broth viscosity. Under this condition, the oil can disperse sufficiently in broth which is very important for lipase production. These results indicate that morphology changes affected the lipase production significantly for R. chinensis and the aggregated mycelia were suggested to achieve high lipase production.

Culture condition improvement for whole-cell lipase production in submerged fermentation by Rhizopus chinensis using statistical method

Rhizopus chinensis CCTCC M201021 was a versatile strain capable of producing whole-cell lipase with synthetic activity in submerged fermentation. In order to improve the production of whole-cell lipase and study the culture conditions systematically, the combination of taguchi method and response surface methodology was performed. Taguchi method was used for the initial optimization, and eight factors viz., maltose, olive oil, peptone, K2HPO4, agitation, inoculum size, fermentation volume and pH were selected for this study. The whole-cell lipase activity yield was two times higher than the control experiment under initial optimal conditions, and four significant factors (inoculum, olive oil, fermentation volume and peptone) were selected to test the effect on the lipase production using response surface methodology. The optimal fermentation parameters for enhanced whole-cell lipase yield were found to be: inoculum 4.25 x 10(8) spores/L, olive oil 2.367% (w/v), fermentation volume 18 mL/250 mL flask, peptone 4.06% (w/v). Subsequent experimental trails confirmed the validity of the model. These optimal culture conditions in the shake flask led to a lipase yield of 13875 U/L, which 120% increased compare with the non-optimized conditions.

The polarisome component SpaA localises to hyphal tips of Aspergillus niger and is important for polar growth

Hyphal tip growth is a key feature of filamentous fungi, however, the molecular mechanism(s) that regulate cell polarity are poorly understood. On the other hand, much more is known about polarised growth in the yeast Saccharomyces cerevisiae. Here, the proteins Spa2p, Bni1p, Bud6p and Pea2p form a protein complex named the polarisome known to be important for the assurance of polar growth. We searched the genome of Aspergillus niger and identified homologues for Spa2p, Bni1p, Bud6p but not for Pea2p. We characterised the function of the Spa2p homologue SpaA by determining its cellular localisation and by constructing deletion and overexpressing mutant strains. SpaA was found to be localised exclusively at the hyphal tip, suggesting that SpaA can be used as marker for polarisation. Deletion and overexpression of spaA resulted in reduced growth rate, increased hyphal diameter and polarity defects, indicating that one of the functions of SpaA is to ensure polarity maintenance. In addition, we could show that SpaA is able to complement the defective haploid invasive growth phenotype of a S. cerevisiae SPA2 null mutant. We suggest that the function of SpaA is to ensure maximal polar growth rate in A. niger.

Microparticle-enhanced cultivation of filamentous microorganisms: increased chloroperoxidase formation by Caldariomyces fumago as an example

Microparticle-enhanced cultivation (MPEC) was applied as a novel method for improved biomass and product formation during cultivation of filamentous microorganisms. Exemplarily, chloroperoxidase (CPO) formation by Caldariomyces fumago was analyzed in the presence and absence of microparticles of different size. Particles of approximately 500 microm in diameter had no effect on growth morphology or productivity of CPO formation by C. fumago. In contrast particles of < or =42 microm in diameter led to the dispersion of the C. fumago mycelia up to the level of single hyphae. Under these conditions the maximum specific productivity of CPO formation was enhanced about fivefold and an accumulated CPO activity in the culture supernatant of more than 1,000 U mL(-1) was achieved after 10-12 days of cultivation. In addition, the novel cultivation method also showed a positive effect on growth characteristics of other filamentous microorganisms proven by the stimulation of single hyphae/cell formation.

Population balance modeling of the conidial aggregation of Aspergillus niger

Numerous biotechnological production processes are based on the submerse cultivation of filamentous fungi. Process design, however, is often hampered by the complex growth pattern of these organisms. In the morphologic development of coagulating filamentous fungi, like Aspergillus niger, conidial aggregation is the first step of filamentous morphogenesis. For a proper description of this phenomenon it is necessary to characterize conidial populations. Kinetic studies performed with an in-line particle size analyzer suggested that two distinct aggregation steps have to be considered. The first step of conidial aggregation starts immediately after inoculation. Both the rate constants of formation and disintegration of aggregates have been determined by measuring the concentration of conidia at the beginning of the cultivation and the concentration of particles at steady state during the first hours of cultivation. In contrast to the first aggregation step, where the collision of conidia is presumed to be responsible for the process, the second aggregation step is thought to be initiated by germination of conidia. Growing hyphae provide additional surface for the attachment of non- germinated conidia, which leads to a strong decrease in particle concentration. The specific hyphal length growth rate and the ratio of particle concentration to the growing adhesion hyphal surface are decisive matters of the second aggregation step. Both aggregation steps can be described by population dynamics and simulated using the program package PARSIVAL (PARticle SIze eVALution) for the treatment of general particle population balances.

Morphological patterns of Aspergillus niger biofilms and pellets related to lignocellulolytic enzyme productivities

AIMS

To study the morphological patterns of Aspergillus niger during biofilm formation on polyester cloth by using cryo-scanning electron microscopy related to lignocellulolytic enzyme productivity.

METHODS AND RESULTS

Biofilm and pellet samples obtained from flask cultures were examined at -80 degrees C in a LEO PV scanning electron microscope. Spore adhesion depends on both its rough surface and adhesive substances that form a pad between spore and support. An extracellular matrix surrounding germ tubes and hyphae was also seen. Biofilm mycelia showed an orderly distribution forming surface and inner channels, while pellets showed highly intertwined superficial hyphae and a densely packed deep mycelium. Morphological differences between both types of culture correlated with differences in enzyme volumetric and specific productivities. Biofilm cultures produced higher filter paper cellulase, endoglucanase, beta-glucosidase and xylanase volumetric and specific productivities than submerged cultures.

CONCLUSIONS

Fungal biofilms are morphologically efficient systems for enzyme production. Favourable physiological aspects are shared with solid state fermentation, but fungal biofilms present better possibilities for process control and scale-up.

SIGNIFICANCE AND IMPACT OF THE STUDY

The results of this study support the importance of morphology in the productivity of fungal submerged processes, placing biofilms in a preferential category.

Metabolic flux analysis using stoichiometric models for Aspergillus niger: comparison under glucoamylase-producing and non-producing conditions

Aspergillus niger AB1.13 cultures with glucoamylase production (with D-glucose as substrate) and without glucoamylase production (with D-xylose as substrate) were characterized by metabolic flux analysis. Two comprehensive metabolic models for d-glucose- as well as for D-xylose-consumption were used to quantify and compare the metabolic fluxes through the central pathways of carbon metabolism at different pH-values. The models consist of the most relevant metabolic pathways for A. niger including glycolysis, pentose-phosphate pathway, citrate cycle, energy metabolism and anaplerotic reactions comprising two intracellular compartments, the cytoplasm and mitochondrion. When D-xylose was used as the sole carbon source, the relative flux of the substrate through the oxidative pentose-phosphate pathway (PPP) via G6P-dehydrogenase was unaffected by the pH-value of the culture medium. About 30% of D-xylose consumed was routed through the oxidative PPP. In contrast, the flux of D-glucose (i.e., under glucoamylase-producing conditions) through the oxidative PPP was remarkably higher and, in addition was significantly affected by the pH-value of the culture medium (40% at pH 5.5, 56% at pH 3.7, respectively). Summarizing, the flux through the PPP under glucoamylase producing conditions was 30-90% higher than for non-producing conditions.

Selection of reference genes for normalisation of specific gene quantification data of Aspergillus niger

Aspergillus niger is a widely used expression host for homologous and heterologous protein production in biotechnological processes. In order to increase product yields, a thorough optimisation of these cultivation processes is necessary. Considering mRNA as the key molecule, which transports the genetic information between DNA and protein production side, the quantification of product specific gene expression provides useful information about product formation already on the level of transcription. Quantitative reverse transcription polymerase chain reaction (qRT-PCR) is a powerful tool to obtain data about gene transcription. However, using this technique the choice of an appropriate reference system is a crucial aspect to provide optimal data normalisation. A prominent approach is the use of so called housekeeping genes as internal references. However, validation of the usability of these reference genes is the fundamental step before starting with qRT-PCR experiments. Adequate reference genes for A. niger have not been published so far. Therefore, 10 possible candidate genes from different functional classes were selected and their applicability as internal references validated. Transcript levels of these genes were compared in sets of 9, 41 and 19 samples from diverse cultivations of A. niger. Under the chosen experimental conditions, the genes act, sarA and cox5 have been identified as genes with the most stable gene expression. The three reference genes were used to normalise qRT-PCR data for glaA gene expression which showed a high correlation with glucoamylase production in continuous cultivations.

Physiological characterization of xylose metabolism inAspergillus niger under oxygen-limited conditions

The physiology of Aspergillus niger was studied under different aeration conditions. Five different aeration rates were investigated in batch cultivations of A. niger grown on xylose. Biomass, intra- and extra-cellular metabolites profiles were determined and ten different enzyme activities in the central carbon metabolism were assessed. The focus was on organic acid production with a special interest in succinate production. The fermentations revealed that oxygen limitation significantly changes the physiology of the micro-organism. Changes in extra cellular metabolite profiles were observed, that is, there was a drastic increase in polyol production (erythritol, xylitol, glycerol, arabitol, and mannitol) and to a lesser extent in the production of reduced acids (malate and succinate). The intracellular metabolite profiles indicated changes in fluxes, since several primary metabolites, like the intermediates of the TCA cycle accumulated during oxygen limitation (on average three fold increase). Also the enzyme activities showed changes between the exponential growth phase and the oxygen limitation phase. In general, the oxygen availability has a significant impact on the physiology of this fungus causing dramatic alterations in the central carbon metabolism that should be taken into account in the design of A. niger as a succinate cell factory.

Production of indole diterpenes by Aspergillus alliaceus

Production of two related indole diterpenes (differing by a dimethyl leucine side chain) by Aspergillus alliaceus was improved through several pilot scale fermentations. Media were optimized through focus primarily on initial increases, as well as mid-cycle additions, of carbon and nitrogen sources. Fermentation conditions were improved by varying ventilation conditions using various combinations of air flowrate and back-pressure set points. Production improvements were quantified based on total indole diterpene concentration as well as the ratio of the major-to-minor by-product components. Those changes with a positive substantial impact primarily on total indole diterpene concentration included early cycle glycerol shots and enhanced ventilation conditions (high air flowrate, low back-pressure). Those changes with a significant impact primarily on ratio included higher initial cerelose, soybean oil, monosodium glutamate, tryptophan, or ammonium sulfate concentrations, higher broth pH, and enhanced ventilation conditions. A few changes (higher initial glycerol and monosodium glutamate concentrations) resulted in less notable and desirable titer or ratio changes when implemented individually, but they were adopted to more fully realize the impact of other improvements or to simplify processing. Overall, total indole diterpene titers were improved at the 600 L pilot scale from 125-175 mg/L with a ratio of about 2.1 to 200-260 mg/L with a ratio of about 3.3-4.5. Thus, the ability to optimize total indole diterpene titer and/or ratio readily exists for secondary metabolite production using Aspergillus cultures.

Enhancement of bioconversion of high-molecular mass polycyclic aromatic hydrocarbons in contaminated non-sterile soil by litter-decomposing fungi

With the focus on alternative microbes for soil-bioremediation, 18 species of litter-decomposing basidiomycetous fungi were screened for their ability to grow on different lignocellulosic substrates including straw, flax and pine bark as well as to produce ligninolytic enzymes, namely laccase and manganese peroxidase. Following characteristics have been chosen as criteria for the strain selection: (i) the ability to grow at least on one of the mentioned materials, (ii) production of either of the ligninolytic enzymes and (iii) the ability to invade non-sterile soil. As the result, eight species were selected for a bioremediation experiment with an artificially contaminated soil (total polycyclic aromatic hydrocarbon (PAH) concentration 250 mg/kg soil). Up to 70%, 86% and 84% of benzo(a)anthracene, benzo(a)pyrene, and dibenzo(a,h)anthracene, respectively, were removed in presence of fungi while the indigenous microorganisms converted merely up to 29%, 26% and 43% of these compounds in 30 days. Low molecular-mass PAHs studied were easily degraded by soil microbes and only anthracene degradation was enhanced by the fungi as well. The agaric basidiomycetes Stropharia rugosoannulata and Stropharia coronilla were the most efficient PAH degraders among the litter-decomposing species used.