Aspergillus oryzae in solid-state and submerged fermentations. Progress report on a multi-disciplinary project

Solid-State Fermented Pineapple Peel: A Novel Food Ingredient with Antioxidant and Anti-Inflammatory Properties

It has been reported that pineapple (Ananas comosus) contains healthy nutrients and phytochemicals associated with antioxidant and anti-inflammatory capacities. However, a substantial amount of pineapple residue is produced due to a lack of valorization applications at the industrial scale, resulting in the loss of valuable nutrients. Solid-state fermentation (SSF) is proposed as an innovative strategy to enhance the release of bound phenolics from pineapple residues. In this work, the effects of SSF of pineapple peels with Lactobacillus plantarum, Lactobacillus rhamnosus, and Aspergillus oryzae on the release of phenolic compounds and their antioxidant and anti-inflammatory activities were evaluated, respectively. Pineapple peel extracts after SSF showed an increase in the release of phenolic compounds (248.11% with L. plantarum, 182% with A. oryzae, and 180.10% with L. rhamnosus), which led to an increase in the cellular antioxidant (81.94% with L. rhamnosus) and anti-inflammatory potential (nitric oxide inhibition of 62% with L. rhamnosus) compared to non-fermented extracts. Therefore, SSF of pineapple peels with L. plantarum, L. rhamnosus, and A. oryzae thrives as a new approach for the production of secondary metabolites with remarkable biological benefits, which can be the precursors for novel biofortified and nutraceutical-enriched foods that meet the needs of the most demanding and health-conscious consumers.

Fungal Proteins from Sargassum spp. Using Solid-State Fermentation as a Green Bioprocess Strategy

The development of green technologies and bioprocesses such as solid-state fermentation (SSF) is important for the processing of macroalgae biomass and to reduce the negative effect of Sargassum spp. on marine ecosystems, as well as the production of compounds with high added value such as fungal proteins. In the present study, Sargassum spp. biomass was subjected to hydrothermal pretreatments at different operating temperatures (150, 170, and 190 °C) and pressures (3.75, 6.91, and 11.54 bar) for 50 min, obtaining a glucan-rich substrate (17.99, 23.86, and 25.38 g/100 g d.w., respectively). The results indicate that Sargassum pretreated at a pretreatment temperature of 170 °C was suitable for fungal growth. SSF was performed in packed-bed bioreactors, obtaining the highest protein content at 96 h (6.6%) and the lowest content at 72 h (4.6%). In contrast, it was observed that the production of fungal proteins is related to the concentration of sugars. Furthermore, fermentation results in a reduction in antinutritional elements, such as heavy metals (As, Cd, Pb, Hg, and Sn), and there is a decrease in ash content during fermentation kinetics. Finally, this work shows that Aspergillus oryzae can assimilate nutrients found in the pretreated Sargassum spp. to produce fungal proteins as a strategy for the food industry.

Aspergillus oryzae Grown on Rice Hulls Used as an Additive for Pretreatment of Starch-Containing Wastewater from the Pulp and Paper Industry

From an industrial point of view, the use of microorganisms as a wastewater bioremediation practice represents a sustainable and economic alternative for conventional treatments. In this work, we investigated the starch bioremediation of paper mill wastewater (PMW) with Aspergillus oryzae. This amylase-producing fungus was tested in submerged fermentation technology (SmF) and solid-state fermentation (SSF) on rice hulls. The tests were conducted to assay the concentration of the reducing sugars on paper mill wastewater. The bioremediation of starch in the wastewater was carried out by A. oryzae, which proved capable of growing in this complex media as well as expressing its amylase activity.

Biofilm formation in clinically relevant filamentous fungi: a therapeutic challenge

Biofilms are highly-organized microbial communities attached to a biotic or an abiotic surface, surrounded by an extracellular matrix secreted by the biofilm-forming cells. The majority of fungal pathogens contribute to biofilm formation within tissues or biomedical devices, leading to serious and persistent infections. The clinical significance of biofilms relies on the increased resistance to conventional antifungal therapies and suppression of the host immune system, which leads to invasive and recurrent fungal infections. While different features of yeast biofilms are well-described in the literature, the structural and molecular basis of biofilm formation of clinically related filamentous fungi has not been fully addressed. This review aimed to address biofilm formation in clinically relevant filamentous fungi.

The characteristics of insoluble softwood substrates affect fungal morphology, secretome composition, and hydrolytic efficiency of enzymes produced by Trichoderma reesei

BACKGROUND

On-site enzyme production using Trichoderma reesei can improve yields and lower the overall cost of lignocellulose saccharification by exploiting the fungal gene regulatory mechanism that enables it to continuously adapt enzyme secretion to the substrate used for cultivation. To harness this, the interrelation between substrate characteristics and fungal response must be understood. However, fungal morphology or gene expression studies often lack structural and chemical substrate characterization. Here, T. reesei QM6a was cultivated on three softwood substrates: northern bleached softwood Kraft pulp (NBSK) and lodgepole pine pretreated either by dilute-acid-catalyzed steam pretreatment (LP-STEX) or mild alkaline oxidation (LP-ALKOX). With different pretreatments of similar starting materials, we presented the fungus with systematically modified substrates. This allowed the elucidation of substrate-induced changes in the fungal response and the testing of the secreted enzymes' hydrolytic strength towards the same substrates.

RESULTS

Enzyme activity time courses correlated with hemicellulose content and cellulose accessibility. Specifically, increased amounts of side-chain-cleaving hemicellulolytic enzymes in the protein produced on the complex substrates (LP-STEX; LP-ALKOX) was observed by secretome analysis. Confocal laser scanning micrographs showed that fungal micromorphology responded to changes in cellulose accessibility and initial culture viscosity. The latter was caused by surface charge and fiber dimensions, and likely restricted mass transfer, resulting in morphologies of fungi in stress. Supplementing a basic cellulolytic enzyme mixture with concentrated T. reesei supernatant improved saccharification efficiencies of the three substrates, where cellulose, xylan, and mannan conversion was increased by up to 27, 45, and 2800%, respectively. The improvement was most pronounced for proteins produced on LP-STEX and LP-ALKOX on those same substrates, and in the best case, efficiencies reached those of a state-of-the-art commercial enzyme preparation.

CONCLUSION

Cultivation of T. reesei on LP-STEX and LP-ALKOX produced a protein mixture that increased the hydrolytic strength of a basic cellulase mixture to state-of-the-art performance on softwood substrates. This suggests that the fungal adaptation mechanism can be exploited to achieve enhanced performance in enzymatic hydrolysis without a priori knowledge of specific substrate requirements.

The Potential of Single-Cell Oils Derived From Filamentous Fungi as Alternative Feedstock Sources for Biodiesel Production

Microbial lipids, also known as single-cell oils (SCOs), are highly attractive feedstocks for biodiesel production due to their fast production rates, minimal labor requirements, independence from seasonal and climatic changes, and ease of scale-up for industrial processing. Among the SCO producers, the less explored filamentous fungi (molds) exhibit desirable features such as a repertoire of hydrolyzing enzymes and a unique pellet morphology that facilitates downstream harvesting. Although several oleaginous filamentous fungi have been identified and explored for SCO production, high production costs and technical difficulties still make the process less attractive compared to conventional lipid sources for biodiesel production. This review aims to highlight the ability of filamentous fungi to hydrolyze various organic wastes for SCO production and explore current strategies to enhance the efficiency and cost-effectiveness of the SCO production and recovery process. The review also highlights the mechanisms and components governing lipogenic pathways, which can inform the rational designs of processing conditions and metabolic engineering efforts for increasing the quality and accumulation of lipids in filamentous fungi. Furthermore, we describe other process integration strategies such as the co-production with hydrogen using advanced fermentation processes as a step toward a biorefinery process. These innovative approaches allow for integrating upstream and downstream processing units, thus resulting in an efficient and cost-effective method of simultaneous SCO production and utilization for biodiesel production.

Ideal Feedstock and Fermentation Process Improvements for the Production of Lignocellulolytic Enzymes

The usage of lignocellulosic biomass in energy production for biofuels and other value-added products can extensively decrease the carbon footprint of current and future energy sectors. However, the infrastructure in the processing of lignocellulosic biomass is not well-established as compared to the fossil fuel industry. One of the bottlenecks is the production of the lignocellulolytic enzymes. These enzymes are produced by different fungal and bacterial species for degradation of the lignocellulosic biomass into its reactive fibers, which can then be converted to biofuel. The selection of an ideal feedstock for the lignocellulolytic enzyme production is one of the most studied aspects of lignocellulolytic enzyme production. Similarly, the fermentation enhancement strategies for different fermentation variables and modes are also the focuses of researchers. The implementation of fermentation enhancement strategies such as optimization of culture parameters (pH, temperature, agitation, incubation time, etc.) and the media nutrient amendment can increase the lignocellulolytic enzyme production significantly. Therefore, this review paper summarized these strategies and feedstock characteristics required for hydrolytic enzyme production with a special focus on the characteristics of an ideal feedstock to be utilized for the production of such enzymes on industrial scales.

Bioactive peptides from food fermentation: A comprehensive review of their sources, bioactivities, applications, and future development

Bioactive peptides (BPs) are specific protein fragments that exert various beneficial effects on human bodies and ultimately influence health, depending on their structural properties and amino acid composition and sequences. By offering promising solutions to solve diverse health issues, the production, characterization, and applications of food-derived BPs have drawn great interest in the current literature and are of particular interest to the food and pharmaceutical industries. The microbial fermentation of protein from various sources is indubitably a novel way to produce BPs with numerous beneficial health effects. Apart from its lower cost as compared to enzymes, the BPs produced from microbial fermentation can be purified without further hydrolysis. Despite these features, current literature shows dearth of information on the BPs produced from food via microbial fermentation. Hence, there is a strong necessity to explore the BPs obtained from food fermentation for the development of commercial nutraceuticals and functional foods. As such, this review focuses on the production of BPs from different food sources, including the extensively studied milk and milk products, with emphasis on microbial fermentation. The structure-activity (antihypertensive, antioxidant, antimicrobial, opiate-like, anti-inflammatory, anticancer/antiproliferative, antithrombotic, hypolipidemic, hypocholesterolemic, and mineral binding) relationship, potential applications, future development, and challenges of BPs obtained from food fermentation are also discussed.

Biofilm Mode of Cultivation Leads to an Improvement of the Entomotoxic Patterns of Two Aspergillus Species

Two fungi, i.e., Aspergillus flavus Link and Aspergillus oryzae (Ahlb.) E. Cohn, were cultivated according to two methodologies, namely submerged and biofilm cultures with the primary aim to use their secondary metabolites the supernatant CL₅₀, and CL₉₀ varied between 1.3% (v/v) to 12.7% (v/v) for incubation times from 24 to 72 h. While the A. flavus supernatant entomotoxicity was higher than this of A. oryzae, the biofilm culture application increased the efficiency of the former. Proteomic analysis of the supernatants revealed discrepancies among the two species and modes of cultivation. Furthermore, the secondary metabolite profiles of both Aspergillus cultures were verified. Aspergillic acid, beta-cyclopiazonic acid, cyclopiazonic acid, ferrineospergillin, flavacol, and spermadin A were most predominant. Generally, these secondary metabolites were present in higher concentrations in the supernatants of A. flavus and biofilm cultures. These molecular identifications correlated positively with entomotoxic activity. Noteworthy, the absence of carcinogenic aflatoxins was remarkable, and it will allow further valorization to produce A. flavus to develop potential biopesticides.

Optimized Bioproduction of Itaconic and Fumaric Acids Based on Solid-State Fermentation of Lignocellulosic Biomass

The bioproduction of high-value chemicals such as itaconic and fumaric acids (IA and FA, respectively) from renewable resources via solid-state fermentation (SSF) represents an alternative to the current bioprocesses of submerged fermentation using refined sugars. Both acids are excellent platform chemicals with a wide range of applications in different market, such as plastics, coating, or cosmetics. The use of lignocellulosic biomass instead of food resources (starch or grains) in the frame of a sustainable development for IA and FA bioproduction is of prime importance. Filamentous fungi, especially belonging to the Aspergillus genus, have shown a great capacity to produce these organic dicarboxylic acids. This study attempts to develop and optimize the SSF conditions with lignocellulosic biomasses using A. terreus and A. oryzae to produce IA and FA. First, a kinetic study of SSF was performed with non-food resources (wheat bran and corn cobs) and a panel of pH and moisture conditions was studied during fermentation. Next, a new process using an enzymatic cocktail simultaneously with SSF was investigated in order to facilitate the use of the biomass as microbial substrate. Finally, a large-scale fermentation process was developed for SSF using corn cobs with A. oryzae; this specific condition showed the best yield in acid production. The yields achieved were 0.05 mg of IA and 0.16 mg of FA per gram of biomass after 48 h. These values currently represent the highest reported productions for SSF from raw lignocellulosic biomass.

Mapping haze-komi on rice koji grains using β-glucuronidase expressing Aspergillus oryzae and mass spectrometry imaging

In sake brewing, the quality of rice koji is evaluated by experienced sake brewers based on visual inspection of the haze, which is defined by the extent of fungal hyphae spread on/into the rice grains. There is an increasing interest in understanding the factors that affect the quality of rice koji, which is dependent on its making process. Several studies have focused on the degree of mycelial penetration (haze-komi) and enzyme production during rice koji production. However, there are limited analytical methods available to monitor hyphal growth on a solid surface. Here we used a β-glucuronidase (GUS)-expressing strain of Aspergillus oryzae to visualize and map the fungal growth on rice koji grains. Observation of indigo color revealed that A. oryzae hyphae penetrated the steamed rice grain in the early stage (24 h) of rice koji-making before spreading on the surface during the later stages. Additionally, hyphae penetrated along the endosperm cells and penetrated the cells to form the sou-haze. Furthermore, mass spectrometry imaging (MSI) of glucose demonstrated that the area of mycelial penetration is directly correlated with the spread of glucose during fermentation. This is the first report on utilizing new tools such as GUS-body-mapping of A. oryzae and MSI to monitor fungal growth during rice koji making.

Water dynamics during solid-state fermentation by Aspergillus oryzae YH6

Water is crucial for microbial growth, heat transfer and substrate hydrolysis, and dynamically changes with time in solid-state fermentation. However, water dynamics in the solid substrate is difficult to define and measure. Here, nuclear magnetic resonance was used to monitor water dynamics during the pure culture of Aspergillus oryzae YH6 on wheat in a model system to mimic solid starter (Qu or Koji) preparation. During fermentation, overall water content gradually decreased from 0.84 to 0.36 g/g, and water activity decreased from 0.99 to 0.93. Water content in different state (bound, immobilized and free) changed differently and all moved to more "bound" direction. The internal water distribution over the substrate matrix also showed a faster reduction inward both in the radical and axial direction. Our findings provide the prerequisites for optimal processes where water dynamics in solid-state fermentation can be monitored and controlled.

Cleavage of poly(cis-1,4-isoprene) rubber as solid substrate by cultures of Gordonia polyisoprenivorans

Potential biotechnological recycling processes for rubber products include the bacterial degradation of poly(cis-1,4-isoprene) (IR) in order to achieve its total biodegradation or its biotransformation into useful products. The actinomycete Gordonia polyisoprenivorans strain VH2 catalyzes the degradation of IR and enables its use as a sole carbon source via β-oxidation. The initial cleavage reaction is catalyzed by the extracellular latex clearing protein (Lcp). This dioxygenase is the key enzyme for the formation of oligo(cis-1,4-isoprene) molecules with different lengths, i.e., numbers of isoprene units. For the first time, IR was used as a solid substrate in 2-l fermenters. Two different particle size fractions (63-500 and 500-1000 μm) and three stirring rates (300, 400 and 500 rpm) were evaluated in the process. An increase of the cell concentration was achieved by using smaller particles and by using lower stirring rates, reaching a final biomass concentration of 0.52 g l^-1 at 300 rpm after 12 days of cultivation. In order to enhance the formation of oligo(cis-1,4-isoprene) molecules, a transposon insertion mutant (TH5) of G. polyisoprenivorans strain VH2 that has lost the ability to transport the partial degradation products into the cells was used, thereby allowing the accumulation of the degradation products in the culture supernatants. Propionate, glucose and glycerol were evaluated as additional carbon sources besides IR, and the highest yields were observed on propionate. In 2-l bioreactors with pH control, different feeding regimes were performed during cultivation by the addition of propionate every 24 or 48 h for 16 days. After liquid-liquid extraction and a derivatization with Girard's T reagent, the oligo(cis-1,4-isoprene) molecules were detected by ESI-MS. The mass distribution of the degradation products was affected by the selection of the extraction solvent, but no influence of longer cultivation periods was detected.

A biotechnology perspective of fungal proteases

Proteases hydrolyze the peptide bonds of proteins into peptides and amino acids, being found in all living organisms, and are essential for cell growth and differentiation. Proteolytic enzymes have potential application in a wide number of industrial processes such as food, laundry detergent and pharmaceutical. Proteases from microbial sources have dominated applications in industrial sectors. Fungal proteases are used for hydrolyzing protein and other components of soy beans and wheat in soy sauce production. Proteases can be produced in large quantities in a short time by established methods of fermentation. The parameters such as variation in C/N ratio, presence of some sugars, besides several other physical factors are important in the development of fermentation process. Proteases of fungal origin can be produced cost effectively, have an advantage faster production, the ease with which the enzymes can be modified and mycelium can be easily removed by filtration. The production of proteases has been carried out using submerged fermentation, but conditions in solid state fermentation lead to several potential advantages for the production of fungal enzymes. This review focuses on the production of fungal proteases, their distribution, structural-functional aspects, physical and chemical parameters, and the use of these enzymes in industrial applications.

Functional analysis of histone deacetylase and its role in stress response, drug resistance and solid-state cultivation in Aspergillus oryzae

In the eukaryotic cell, histone deacetylases (HDACs) play key roles in the regulation of fundamental cellular process such as development regulation, stress response, secondary metabolism and genome integrity. Here, we provide a comprehensive phenotypic analysis using HDAC disruptants in Aspergillus oryzae. Our study revealed that four HDACs, hdaA/Aohda1, hdaB/Aorpd3, hdaD/Aohos2 and hst4/AohstD were involved in stress response, cell wall synthesis and chromatin integrity in A. oryzae. Osmotic stress sensitivity of HDAC disruptants differed between plate cultures and liquid cultures, suggesting that HDACs adapt to the difference environmental conditions. Using a common A. oryzae fermentation medium, rice-koji, we also characterized HDACs related to growth and enzyme production to investigate which HDACs will be required for adaptation to environmental conditions and stress resistances. Because HDACs are widely conserved, our study has broad applications and may inform work with filamentous fungi and other eukaryote.

Glass bead cultivation of fungi: combining the best of liquid and agar media

Production of bioactive compounds and enzymes from filamentous fungi is highly dependent on cultivation conditions. Here we present an easy way to cultivate filamentous fungi on glass beads that allow complete control of nutrient supply. Secondary metabolite production in Fusarium graminearum and Fusarium solani cultivated on agar plates, in shaking liquid culture or on glass beads was compared. Agar plate culture and glass bead cultivation yielded comparable results while liquid culture had lower production of secondary metabolites. RNA extraction from glass beads and liquid cultures was easier than from agar plates and the quality was superior. The system allows simple control of nutrient availability throughout fungal cultivation. This combined with the ease of extraction of nucleic acids and metabolites makes the system highly suitable for the study of gene regulation in response to specific nutrient factors.

Rapid enzyme production and mycelial growth in solid-state fermentation using the non-airflow box

Solid-state fermentation (SSF) has become an attractive alternative to submerged fermentation (SMF) for the production of enzymes, organic acids, and secondary metabolites, while there are many problems during the culture of SSF. We recently created a SSF system using a non-airflow box (NAB) in order to resolve the problems, which enabled the uniform culture in the whole substrate and high yield of many enzymes. In this paper, further characterization of SSF using the NAB was carried out to obtain other advantages. The NAB culture under the fixed environmental condition exhibited a rapid increase in enzyme production at earlier phase during the culture compared with conventional SSF. Total mycelial growth also exhibited the same trend as enzyme production. Thus, the increase in the rate of the enzyme production was thought to mainly be attributed to that of the growth. To support it, it was suggested that the NAB culture resulted in most optimal water activity for the growth just at the log phase. In addition, the NAB culture was able to achieve high reproducibility of enzyme production, derived from uniform condition of the substrate during the culture. The results indicate that the NAB culture has many benefits for SSF.

Development of permeable reactive biobarrier for the removal of PAHs by Trichoderma longibrachiatum

In this work, the formation of permeable reactive biobarriers (PRBBs) using Trichoderma longibrachiatum over nylon sponge as bioreactive medium for removal of polycyclic aromatic hydrocarbons (PAHs) was studied. Colony formation was pretested without PAH presence by inoculation of fungus into nylon sponge. The fungus formed a large quantity of strongly adhesive biofilm among nylon sponge. Afterwards, the ability of the developed bioreactive medium was tested to remediate phenanthrene in aqueous medium and in soil. In aqueous medium, a 90% of phenanthrene concentration reduction was observed after 14 d. However, the pollutant removal in soil requires previous fungus colonization and the attained level was around 70% after 28 d. Subsequently, the formed bioreactive material was used in a glass column reactor to evaluate its application as PRBBs. Mixtures of phenanthrene, benzo[a]anthracene and pyrene at several concentrations, from 100 to 400 μM, were treated. In all cases, the performance of the PRBB was satisfactory and total PAH removals were achieved. These results suggest that PRBBs of T. longibrachiatum supported on nylon sponge can be an effective method for the treatment of PAHs.

Induction of hypocrellin production by Triton X-100 under submerged fermentation with Shiraia sp. SUPER-H168

Hypocrellins are important photodynamic therapy compounds for cancer disease. The effect of surfactants on hypocrellin production of Shiraia sp. SUPER-H168 was evaluated under submerged fermentation condition. The production of hypocrellins could reach 780.6 mg/l with the addition of Triton X-100, confirmed by color reaction, high performance liquid chromatography, electrospray ionization mass spectrometry and nuclear magnetic resonance experiments. According to our observation, treatment of the culture at the beginning of the fermentation was most effective, and the yield of hypocrellins was much lower with the addition of Triton X-100 during the log phase and stationary phase. Shiraia sp. SUPER-H168 could not produce hypocrellin with the addition of other tested surfactants, such as Tween 40, Triton X-114 and SDS. The experimental results indicated that Shiraia sp. SUPER-H168 could not produce hypocrellins without Triton X-100 under submerged fermentation condition.

A novel microplate-based screening strategy to assess the cellulolytic potential of Trichoderma strains

Bioconversion of lignocellulosic biomass to fuel requires a hydrolysis step to obtain fermentable sugars, generally accomplished by fungal enzymes. An assorted library of cellulolytic microbial strains should facilitate the development of optimal enzyme cocktails specific for locally available feedstocks. Only a limited number of strains can be simultaneously assayed in screening based on large volume cultivation methods, as in shake flasks. This study describes a miniaturization strategy aimed at allowing parallel assessment of large numbers of fungal strains. Trichoderma strains were cultivated stationary on microcrystalline cellulose using flat bottom 24-well plates containing an agarized medium. Supernatants obtained by a rapid centrifugation step of the whole culture plates were evaluated for extracellular total cellulase activity, measured as filter paper activity, using a microplate-based assay. The results obtained were consistent with those observed in shake-flask experiments and more than 300 Trichoderma strains were accordingly characterized for cellulase production. Five strains, displaying on shake-flasks at least 80% of the activity shown by the hyper-cellulolytic mutant Trichoderma Rut-C30, were correctly recognized by the screening on 24-well plates, demonstrating the feasibility of this approach. Cellulase activity distribution for the entire Trichoderma collection is also reported. One strain (T. harzianum Ba8/86) displayed the closest profile to the reference strain Rut-C30 in time course experiments. The method is scalable and addresses a major bottleneck in screening programs, allowing small-scale parallel cultivation and rapid supernatant extraction. It can also be easily integrated with high-throughput enzyme assays and could be suitable for automation.

Can filamentous fungi form biofilms?

The discovery of biofilm formation in bacteria and yeasts has led to a better understanding of microbial ecology and to new insights into the mechanisms of virulence and persistence of pathogenic microorganisms. However, it is generally assumed that filamentous fungi, some of which have a significant impact on our health or our economy, do not form biofilms. In contrast to this assumption, here we discuss recent findings supporting the hypothesis that surface-associated filamentous fungi can form biofilms. Based on these findings and on previous models for bacterial and yeast systems, we propose preliminary criteria and a model for biofilm formation by filamentous fungi.

Morphological quantification of filamentous fungal development using membrane immobilization and automatic image analysis

Mycelial morphology is a critically important process property in industrial fermentations of filamentous micro-organisms, as particular phenotypes are associated with maximum productivity. However, the accurate quantification of complex morphologies still represents a significant challenge in elucidating this relationship. A system has been developed for high-resolution characterisation of filamentous fungal growth on a solid substrate, using membrane immobilization and fully-automatic plug-ins developed for the public domain, Java-based, image-processing software, ImageJ. The system has been used to quantify the microscopic development of Aspergillus oryzae on malt agar, by measuring spore projected area and circularity, the total length of a hyphal element, the number of tips per element, and the hyphal growth unit. Two different stages of growth are described, from the swelling of a population of conidiospores up to fully developed, branched hyphae 24 h after inoculation. Spore swelling expressed as an increase in mean equivalent spore diameter was found to be approximately linear with time. Widespread germination of spores was observed by 8 h after inoculation. From approximately 12 h, the number of tips was found to increase exponentially. The specific growth rate of a population of hyphae was calculated as approximately 0.24-0.27 h(-1). A wide variation in growth kinetics was found within the population. The robustness of the image-analysis system was verified by testing the effect of small variations in the input data.

Filamentous fungi for production of food additives and processing aids

Filamentous fungi are metabolically versatile organisms with a very wide distribution in nature. They exist in association with other species, e.g. as lichens or mycorrhiza, as pathogens of animals and plants or as free-living species. Many are regarded as nature's primary degraders because they secrete a wide variety of hydrolytic enzymes that degrade waste organic materials. Many species produce secondary metabolites such as polyketides or peptides and an increasing range of fungal species is exploited commercially as sources of enzymes and metabolites for food or pharmaceutical applications. The recent availability of fungal genome sequences has provided a major opportunity to explore and further exploit fungi as sources of enzymes and metabolites. In this review chapter we focus on the use of fungi in the production of food additives but take a largely pre-genomic, albeit a mainly molecular, view of the topic.

Comparative profiles of alpha-amylase production in conventional tray reactor and GROWTEK bioreactor

GROWTEK bioreactor was used as modified solid-state fermentor to circumvent many of the problems associated with the conventional tray reactors for solid-state fermentation (SSF). Aspergillus oryzae IFO-30103 produced very high levels of alpha-amylase by modified solid-state fermentation (mSSF) compared to SSF carried out in enamel coated metallic trays utilizing wheat bran as substrate. High alpha-amylase yield of 15,833 U g(-1) dry solid in mSSF were obtained when the fungus were cultivated at an initial pH of 6.0 at 32 degrees C for 54 h whereas alpha-amylase production in SSF reached its maxima (12,899 U g(-1) dry solid ) at 30 degrees C after 66 h of incubation. With the supplementation of 1% NaNO(3), the maximum activity obtained was 19,665 U g(-1) dry solid (24% higher than control) in mSSF, whereas, in SSF maximum activity was 15,480 U g(-1) dry solid in presence of 0.1% Triton X-100 (20% higher than the control).

Development of AFLP-derived, functionally specific markers for environmental persistence studies of fungal strains

The ability to rapidly identify and quantify a microbial strain in a complex environmental sample has widespread applications in ecology, epidemiology, and industry. In this study, we describe a rapid method to obtain functionally specific genetic markers that can be used in conjunction with standard or real-time polymerase chain reaction (PCR) to determine the abundance of target fungal strains in selected environmental samples. The method involves sequencing of randomly cloned AFLP (amplified fragment length polymorphism) products from the target organism and the design of PCR primers internal to the AFLP fragments. The strain-specific markers were used to determine the fate of three industrially relevant fungi, Aspergillus niger, Aspergillus oryzae, and Chaetomium globosum, during a 4 month soil microcosm experiment. The persistence of each of the three fungal strains inoculated separately into intact soil microcosms was determined by PCR analyses of DNA directly extracted from soil. Presence and absence data based on standard PCR and quantification of the target DNA by real-time PCR showed that all three strains declined after inoculation (approximately 14-, 32-, and 4-fold for A. niger, A. oryzae, and C. globosum, respectively) but remained detectable at the end of the experiment, suggesting that these strains would survive for extended periods if released into nature.

Identification of secreted proteins of Aspergillus oryzae associated with growth on solid cereal substrates

Filamentous growth of Aspergillus oryzae on solid cereal substrates involves secretion of substrate converting enzymes and a solid substrate specific polarised hyphal growth phenotype. To identify proteins produced under these specific conditions, the extracts of A. oryzae grown on wheat-based media were analysed using N-terminal sequence analysis. In a submerged wheat-based growth medium of A. oryzae, besides alpha-amylase, also an arabinosidase and xylanase were abundantly produced. In the extracts of A. oryzae grown on wheat-based solid substrate besides alpha-amylase and chitinase, two new proteins of 16 and 27 kDa were identified. These hypothetical proteins showed only close homologies to filamentous fungal proteins.

Solid-state fermentation — are there any biotechnological advantages?

Solid-state fermentation (SSF) has developed in eastern countries over many centuries, and has enjoyed broad application in these regions to date. By contrast, in western countries the technique had to compete with classical submerged fermentation and, because of the increasing pressure of rationalisation and standardisation, it has been widely superseded by classical submerged fermentation since the 1940s. This is mainly because of problems in engineering that appear when scaling up this technique. However, there are several advantages of SSF, for example high productivities, extended stability of products and low production costs, which say much about such an intensive biotechnological application. With increasing progress and application of rational methods in engineering, SSF will achieve higher levels in standardisation and reproducibility in the future. This can make SSF the preferred technique for special fields of application such as the production of enzymes and food.

Branching mutants of Aspergillus oryzae with improved amylase and protease production on solid substrates

To study the relation between the number of hyphal tips and protein secretion during growth on a solid substrate, we have constructed two mutant strains of Aspergillus oryzae with increased hyphal branching. We have analysed hydrolytic enzyme activities during growth on wheat kernels (WK) of A. oryzae strains carrying the disrupted allele of the pclA gene encoding a secretion pathway specific (KEX2-like) endo-protease and the disrupted allele of the pg/pi-tp gene encoding a phosphatidylglycerol/phosphatidylinositol transfer protein. The biomass levels produced by the pclA and pg/pi-tp disrupted strains on wheat-based solid media were similar as found for the wild-type strain. However, the pclA disrupted strain showed much more compact colony morphology than the other two strains. Sporulation of the pclA and pg/pi-tp disrupted strains occurred, respectively, 2 days and 1 day later, compared to the wild type during fermentation on ground WK. During surface growth, microscopic analysis revealed that the hyphal growth unit length (L (hgu)) of the pclA and pg/pi-tp disrupted strains was, on average, 50 and 74% of that of the wild-type strain. This implies that in both mutant strains, a higher branching frequency occurs than in the wild-type strain. Compared to the wild-type strain, the pclA and pg/pi-tp disrupted strains produced at least 50% more amylase, at least 100% more glucoamylase and at least 90% more protease activity levels after growth on WK. These results support the hypothesis that branching mutants with an increased branching frequency can improve the solid state fermentation process.

Identification of growth phenotype-related genes in Aspergillus oryzae by heterologous macroarray and suppression subtractive hybridization

Aspergillus oryzae requires polarized growth for colonization of solid substrates, and this growth phenotype differs from that seen in liquid medium. Various experimental approaches were used to identify genes that are differentially expressed when A. oryzae is grown on wheat kernels and in a wheat-based liquid medium. Hybridization of A. oryzae RNAs to a macroarray bearing cDNAs isolated from a library representing at least 16% of the total number of A. niger genes identified 14 differentially expressed cDNA clones, showing that heterologous macroarray analysis with an A. niger cDNA library can be used to identify regulated gene transcripts in the related species A. oryzae. Moreover, Northern analysis with a selection of eight probes for A. niger genes encoding proteins involved in morphological development and cell wall biosynthesis identified five more differentially expressed genes. A suppression subtractive hybridization procedure revealed another 12 differentially expressed genes. The results presented show that, of the 29 identified genes which are expressed at higher levels during growth on wheat kernels, six encode proteins that are functionally related to polarized growth, four encode products known to be involved in morphogenesis, three code for proteins related to cell wall composition, and nine of the cDNA clones encode novel proteins. These findings pinpoint genes associated with the changes in cellular morphogenesis seen in A. oryzae grown on wheat kernels as opposed to wheat-based liquid medium.