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

Streptomyces produce a broad spectrum of biologically active molecules such as oxytetracycline and rimocidin, which are widely used in human and animal treatments. microparticle-enhanced cultivation (MPEC) is one of the tools used for Streptomyces bioprocesses intensification by the control of mycelial morphology. In the present work, morphological changes of Streptomyces rimosus caused by the addition of 10 µm talc microparticles in MPEC were correlated with the biosynthetic activity of the microorganism. Comparing the runs with and without microparticles, major morphological changes were observed in MPEC, including the deformation of pellets, variation of their size, appearance of hyphae and clumps as well as the aggregation of mycelial objects. The presence of talc microparticles also influenced the levels of the studied secondary metabolites produced by S. rimosus. Comparing control and MPEC runs, the addition of talc microparticles increased the amounts of oxytetracycline (9-fold), 2-acetyl-2-decarboxamido-oxytetracycline (7-fold), milbemycin A3+4[O] (3-fold) and CE 108 (1.5-fold), while rimocidin (27-ethyl) and milbemycin ß11+4[O] production was reduced. In summary, the addition of talc microparticles to S. rimosus cultivations led to the development of smaller morphological forms like hyphae and clumps as well as to the changes in the amounts of secondary metabolites.

Effects of the Coculture Initiation Method on the Production of Secondary Metabolites in Bioreactor Cocultures of Penicillium rubens and Streptomyces rimosus.

Bioreactor cocultures involving Penicillium rubens and Streptomyces rimosus were investigated with regard to secondary metabolite production, morphological development, dissolved oxygen levels, and carbon substrate utilization. The production profiles of 22 secondary metabolites were analyzed, including penicillin G and oxytetracycline. Three inoculation approaches were tested, i.e., the simultaneous inoculation of P. rubens with S. rimosus and the inoculation of S. rimosus delayed by 24 or 48 h relative to P. rubens. The delayed inoculation of S. rimosus into the P. rubens culture did not prevent the actinomycete from proliferating and displaying its biosynthetic repertoire. Although a period of prolonged adaptation was needed, S. rimosus exhibited growth and the production of secondary metabolites regardless of the chosen delay period (24 or 48 h). This promising method of coculture initiation resulted in increased levels of metabolites tentatively identified as rimocidin B, 2-methylthio-cis-zeatin, chrysogine, benzylpenicilloic acid, and preaustinoid D relative to the values recorded for the monocultures. This study demonstrates the usefulness of the delayed inoculation approach in uncovering the metabolic landscape of filamentous microorganisms and altering the levels of secondary metabolites.

Lovastatin production by Aspergillus terreus in membrane gradostat bioreactor with two-stage feeding strategy.

Lovastatin is a blood cholesterol-lowering agent and is produced as a secondary metabolite by Aspergillus terreus. Microbial production of this drug is carried out in solid-state or submerged culture, and due to difficulties of controlling the procedure parameters in solid-state method, the submerged method is conventional for industrial production. Although the submerged method is widely used, but this method damages the morphology of fungus due to shear stress caused by stirring. Since the morphology of fungus is a key factor in lovastatin production, using a bioreactor that causes the least damage to it, can improve the lovastatin production. In this paper, for the first time, it has been shown that the membrane gradostat bioreactor is suitable for lovastatin production, using A. terreus, due to providing suitable environmental conditions, therefore, it can be implemented as an alternative method for lovastatin production. Furthermore, it was found that implementing two-stage feeding, using different ratios of Carbon to Nitrogen in the culture medium, makes the lovastatin production to be 5 times more than one-stage feeding. Finally, it is shown that adding Zinc and Magnesium at the second stage further increases lovastatin production by 18%.

Complete genome sequence of lovastatin producer Aspergillus terreus ATCC 20542 and evaluation of genomic diversity among A. terreus strains.

In the present study, the complete genome of a filamentous fungus Aspergillus terreus ATCC 20542 was sequenced, assembled, and annotated. This strain is mainly recognized for being a model wild-type lovastatin producer and a parental strain of high-yielding industrial mutants. It is also a microorganism with a rich repertoire of secondary metabolites that has been a subject of numerous bioprocess-related studies. In terms of continuity, the genomic sequence provided in this work is of the highest quality among all the publicly available genomes of A. terreus strains. The comparative analysis revealed considerable diversity with regard to the catalog of biosynthetic gene clusters found in A. terreus. Even though the cluster of lovastatin biosynthesis was found to be well-conserved at the species level, several unique genes putatively associated with metabolic functions were detected in A. terreus ATCC 20542 that were not detected in other investigated genomes. The analysis was conducted also in the context of the primary metabolic pathways (sugar catabolism, biomass degradation potential, organic acid production), where the visible differences in gene copy numbers were detected. However, the species-level genomic diversity of A. terreus was more evident for secondary metabolism than for the well-conserved primary metabolic pathways. The newly sequenced genome of A. terreus ATCC 20542 was found to harbor several unique sequences, which can be regarded as interesting subjects for future experimental efforts on A. terreus metabolism and fungal biosynthetic capabilities. KEY POINTS: • The high-quality genome of Aspergillus terreus ATCC 20542 has been assembled and annotated. • Comparative analysis with other sequenced Aspergillus terreus strains has revealed considerable diversity in biosynthetic gene repertoire, especially related to secondary metabolism. • The unique genomic features of A. terreus ATCC 20542 are discussed.

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.

Evaluating the outcomes of submerged co-cultivation: production of lovastatin and other secondary metabolites by Aspergillus terreus in fungal co-cultures.

The goal of the study was to compare the production of secondary metabolites by Aspergillus terreus ATCC 20542 under the conditions of submerged mono- and co-cultivation. The suggested experimental scheme encompassed a diverse set of co-culture initiation strategies differing mostly with respect to the development stage of tested fungal strains at the moment of their confrontation. Three species of filamentous fungi exhibiting distinct patterns of morphological evolution under submerged conditions, namely Penicillium rubens, Chaetomium globosum, and Mucor racemosus, were selected as the co-cultivation partners of A. terreus. The choice of the co-cultivated species and the approach of co-culture triggering noticeably influenced the levels of lovastatin (mevinolinic acid), (+)-geodin, asterric acid, and butyrolactone I in the broth. Even though the evaluated co-cultures did not lead to the increased titers of lovastatin relative to standard monocultures, the biosynthesis of the remaining three metabolites was either enhanced or inhibited depending on the experimental variant. The production of butyrolactone I turned out to be particularly affected by the presence of C. globosum. Interestingly, in the A. terreus/C. globosum co-cultures, the decrease of lovastatin concentration was recorded. According to the most probable scenario, lovastatin was in this case converted to monacolin J acid, a polyketide molecule that may be applied as a substrate for the synthesis of statin drugs. The study revealed that the spores of two distinct fungal species, namely A. terreus and C. globosum, co-agglomerate under submerged conditions to form pellets. Finally, the biosynthetic performance of co-cultures involving four fungal species was evaluated.

Influence of the construction of porous spargers on lovastatin production by Aspergillus terreus ATCC 20,542 in a laboratory bubble column.

In bubble column bioreactors, the hydrodynamic behavior like mixing time, bubble size and morphology of filamentous fungi are influenced by the construction of spargers. Sparger pore size is an important factor influencing formation of bubbles. In this study for the first time, a 5-L bubble column bioreactor with different porous spargers was used to investigate the effect of mean air bubble diameter (at 0.36, 0.18 and 0.09 cm) on fungal growth, broth viscosity, fungal pellet morphology and lovastatin production by the filamentous fungus Aspergillus terreus. All cultivations were carried out at air flow rate equal to 0.5 Lair L-1 min-1. The viscosity of the broth was influenced by both biomass concentration and size of the fungal pellets. The highest values of viscosity were observed at bubbles of 0.09 cm diameter after 192 h of cultivation. The largest fluffy pellets and the highest yield of lovastatin (443 mg/L) were obtained at air bubbles diameter of 0.18 cm. Lovastatin yield on biomass growth in this condition was, respectively, 1.7-fold and 3.5-fold higher than in the cultivations performed with air bubbles of 0.36 and 0.09 cm diameters. These laboratory scale experiment indicates that air bubble diameter has the impact on lovastatin production and A. terreus culture conditions.

Production of lovastatin and itaconic acid by Aspergillus terreus: a comparative perspective.

Aspergillus terreus is a textbook example of an industrially relevant filamentous fungus. It is used for the biotechnological production of two valuable metabolites, namely itaconic acid and lovastatin. Itaconic acid serves as a precursor in polymer industry, whereas lovastatin found its place in the pharmaceutical market as a cholesterol-lowering statin drug and a precursor for semisynthetic statins. Interestingly, their biosynthetic gene clusters were shown to reside in the common genetic neighborhood. Despite the genomic proximity of the underlying biosynthetic genes, the production of lovastatin and itaconic acid was shown to be favored by different factors, especially with respect to pH values of the broth. While there are several reviews on various aspects of lovastatin and itaconic acid production, the survey on growth conditions, biochemistry and morphology related to the formation of these two metabolites has never been presented in the comparative manner. The aim of the current review is to outline the correlations and contrasts with respect to process-related and biochemical discoveries regarding itaconic acid and lovastatin production by A. terreus.

Induction of secondary metabolism of Aspergillus terreus ATCC 20542 in the batch bioreactor cultures.

Cultivation of Aspergillus terreus ATCC 20542 in a stirred tank bioreactor was performed to induce the biosynthesis of secondary metabolites and provide the bioprocess-related insights into the metabolic capabilities of the investigated strain. The activation of biosynthetic routes was attempted by the diversification of process conditions and growth media. Several strategies were tested, including the addition of rapeseed oil or inulin, changing the concentration of nitrogen source, reduction of chlorine supply, cultivation under saline conditions, and using various aeration schemes. Fifteen secondary metabolites were identified in the course of the study by using ultra-high performance liquid chromatography coupled with mass spectrometry, namely mevinolinic acid, 4a,5-dihydromevinolinic acid, 3α-hydroxy-3,5-dihydromonacolin L acid, terrein, aspulvinone E, dihydroisoflavipucine, (+)-geodin, (+)-bisdechlorogeodin, (+)-erdin, asterric acid, butyrolactone I, desmethylsulochrin, questin, sulochrin, and demethylasterric acid. The study also presents the collection of mass spectra that can serve as a resource for future experiments. The growth in a salt-rich environment turned out to be strongly inhibitory for secondary metabolism and the formation of dense and compact pellets was observed. Generally, the addition of inulin, reducing the oxygen supply, and increasing the content of nitrogen source did not enhance the production of examined molecules. The most successful strategy involved the addition of rapeseed oil to the chlorine-deficient medium. Under these conditions, the highest levels of butyrolactone I, asterric acid, and mevinolinic acid were achieved and the presence of desmethylsulochrin and (+)-bisdechlorogeodin was detected in the broth. The constant and relatively high aeration rate in the idiophase was shown to be beneficial for terrein and (+)-geodin biosynthesis.

Morphology engineering of basidiomycetes for improved laccase biosynthesis.

OBJECTIVE: This work is the first application of a morphological engineering technique called microparticle-enhanced cultivation (MPEC) aimed at the facilitation of laccase production in the submerged cultures by two basidiomycetes species Cerrena unicolor and Pleurotus sapidus. RESULTS: The positive effect of the applied 10 µm Al2O3 microparticles at concentrations from 5 to 30 g Al2O3 l(-1) was shown. Laccase activity increased 3.5-fold for C. unicolor and 2-fold for P. sapidus at 15 g Al2O3 l(-1) on 9 and 14 day of the cultivation, respectively, compared to the control culture without microparticles. The increase of laccase activity in the cultivation broths was caused by the action of Al2O3 microparticles on the agglomeration of hyphae. It led to the decrease of the size of the pellets, (on average by 2 mm for C. unicolor), the change of their shape (star-shaped pellets for C. unicolor) and the change of their structure (more compact pellets for P. sapidus). CONCLUSIONS: Application of MPEC for the submerged cultures of two laccase-producing basidiomycetes proved successful in increasing of enzyme production.

Modern morphological engineering techniques for improving productivity of filamentous fungi in submerged cultures.

Morphological engineering techniques have recently gained popularity as they are used for increasing the productivity of a variety of metabolites and enzymes in fungi growing in submerged cultures. Their action is mainly associated with the changes they evoke in fungal morphology. Traditional morphological engineering approaches include manipulation of spore concentration, pH-shifting and mechanical stress exerted by stirring and aeration. As the traditional methods proved to be insufficient, modern techniques such as changes of medium osmolality or addition of mineral microparticles to the media (microparticle-enhanced cultivation, MPEC) were proposed. Despite the fact that this area of knowledge is still being developed, there are a fair amount of scientific articles concerning the cultivations of filamentous fungi with the use of these techniques. It was described that in Ascomycetes fungi both MPEC or change of osmolality successfully led to the change of mycelial morphology, which appeared to be favorable for increased productivity of secondary metabolites and enzymes. There are also limited but very promising reports involving the successful application of MPEC with Basidiomycetes species. Despite the fact that the mineral microparticles behave differently for various microorganisms, being strain and particle specific, the low cost of its application is a great benefit. This paper reviews the application of the modern morphology engineering techniques. The authors critically assess the advantages, shortcomings, and future prospects of their application in the cultivation of fungi.

Influence of oxygen on lovastatin biosynthesis by Aspergillus terreus ATCC 20542 quantitatively studied on the level of individual pellets.

Despite oxygen is believed to be the most important environmental factor for any aerobic microbial process, the quantitative studies of its influence on growth and metabolite formation on the level of individual pellets formed by filamentous fungi were seldom performed. Never was it made for lovastatin producer Aspergillus terreus ATCC20542. Thus, this work is a quantitative study of oxygen transfer into A. terreus pellets during lovastatin biosynthesis in the shake flask culture. The basic measurement tool was an oxygen microprobe allowing for obtaining oxygen concentration profiles in the pellets. The pellets of various sizes from 1,600 to 6,400 µm exerting different oxygen transfer conditions were studied. Also various initial concentrations of carbon source were applied to change the conditions of biological reaction running in the pellets. Effective diffusivities in A. terreus pellets ranged from 643 to 1,342 µm s(-1) dependent on their size and structure. It occurred that only the smallest pellets of diameter equal to about 1,400 µm were fully penetrated by oxygen. What is more, apart from the size of pellets, the appropriate lactose concentration was required to effectively produce lovastatin. Its value was correlated with oxygen concentration on the surface of the pellet and could not be either too high, as the aforementioned oxygen level tended then to zero, or too low, as despite high oxygen concentration no biological reaction ran in the pellet and no lovastatin was formed.

Validation of a new image analysis procedure for quantifying filamentous bacteria in activated sludge.

Quantification of filamentous bacteria in activated sludge systems can be made by manual counting under a microscope or by the application of various automated image analysis procedures. The latter has been significantly developed in the last two decades. In this work a new method based upon automated image analysis techniques was elaborated and presented. It consisted of three stages: (a) Neisser staining, (b) grabbing of microscopic images, and (c) digital image processing and analysis. This automated image analysis procedure possessed the features of novelty. It simultaneously delivered data about aggregates and filaments in an individual calculation routine, which is seldom met in the procedures described in the literature so far. What is more important, the macroprogram performing image processing and calculation of morphological parameters was written in the same software which was used for grabbing of images. Previously published procedures required using two different types of software, one for image grabbing and another one for image processing and analysis. Application of this new procedure for the quantification of filamentous bacteria in the full-scale as well as laboratory activated sludge systems proved that it was simple, fast and delivered reliable results.

Investigating the Stirred Tank Bioreactor Co-Cultures of the Secondary Metabolite Producers Streptomyces noursei and Penicillium rubens.

The stirred tank bioreactor co-cultures of the filamentous fungus Penicillium rubens and actinomycete Streptomyces noursei were studied with regard to secondary metabolite (SM) production, sugar consumption, and dissolved oxygen levels. In addition to the quantitative analysis of penicillin G and nystatin A1, the broad repertoire of 22 putatively identified products was semi-quantitatively evaluated with the use of UPLC-MS. Three co-cultivation variants differing with respect to the co-culture initiation method (i.e., the simultaneous inoculation of P. rubens and S. noursei and the 24 or 48 h inoculation delay of S. noursei relative to P. rubens) were investigated. All the co-cultures were carried out in parallel with the corresponding monoculture controls. Even though S. noursei showed the tendency to outperform P. rubens and inhibit the production of fungal secondary metabolites, the approach of simultaneous inoculation was effective in terms of enhancing the production of some S. noursei SMs, namely desferrioxamine E, deshydroxynocardamine, and argvalin. S. noursei displayed the capability of adaptation and SM production even after being inoculated into the 24 or 48 h culture of P. rubens. Interestingly, S. noursei turned out to be more efficient in terms of secondary metabolite production when its inoculation time relative to P. rubens was delayed by 48 h rather than by 24 h. The study demonstrated that the prolongation of inoculation delays can be beneficial for production-related performance in some co-culture systems.

Production of secondary metabolites in stirred tank bioreactor co-cultures of Streptomyces noursei and Aspergillus terreus.

The focus of the study was to characterize the bioprocess kinetics and secondary metabolites production in the novel microbial co-cultivation system involving Streptomyces noursei ATCC 11455 (the producer of an antifungal substance known as nystatin) and Aspergillus terreus ATCC 20542 (the source of lovastatin, a cholesterol-lowering drug). The investigated "A. terreus vs. S. noursei" stirred tank bioreactor co-cultures allowed for the concurrent development and observable biosynthetic activity of both species. In total, the production profiles of 50 secondary metabolites were monitored over the course of the study. The co-cultures were found to be effective in terms of enhancing the biosynthesis of several metabolic products, including mevinolinic acid, an acidic form of lovastatin. This work provided a methodological example of assessing the activity of a given strain in the co-culture by using the substrates which can be metabolized exclusively by this strain. Since S. noursei was shown to be incapable of lactose utilization, the observed changes in lactose levels were attributed to A. terreus and thus confirmed its viability. The study was complemented with the comparative microscopic observations of filamentous morphologies exhibited in the co-cultures and corresponding monocultures.

"Microbial Wars" in a Stirred Tank Bioreactor: Investigating the Co-Cultures of Streptomyces rimosus and Aspergillus terreus, Filamentous Microorganisms Equipped With a Rich Arsenal of Secondary Metabolites.

Microbial co-cultivation is an approach frequently used for the induction of secondary metabolic pathways and the discovery of novel molecules. The studies of this kind are typically focused on the chemical and ecological aspects of inter-species interactions rather than on the bioprocess characterization. In the present work, the co-cultivation of two textbook producers of secondary metabolites, namely Aspergillus terreus (a filamentous fungus used for the manufacturing of lovastatin, a cholesterol-lowering drug) and Streptomyces rimosus (an actinobacterial producer of an antibiotic oxytetracycline) in a 5.5-L stirred tank bioreactor was investigated in the context of metabolic production, utilization of carbon substrates and dissolved oxygen levels. The cultivation runs differed in terms of the applied co-culture initiation strategy and the composition of growth medium. All the experiments were performed in three bioreactors running in parallel (corresponding to a co-culture and two respective monoculture controls). The analysis based upon mass spectrometry and liquid chromatography revealed a broad spectrum of more than 40 secondary metabolites, including the molecules identified as the oxidized derivatives of rimocidin and milbemycin that were observed solely under the conditions of co-cultivation. S. rimosus showed a tendency to dominate over A. terreus, except for the runs where S. rimosus was inoculated into the already developed bioreactor cultures of A. terreus. Despite being dominated, the less aggressive strain still had an observable influence on the production of secondary metabolites and the utilization of substrates in co-culture. The monitoring of dissolved oxygen levels was evaluated as a fast approach of identifying the dominant microorganism during the co-cultivation process.

Quantitative Morphological Analysis of Filamentous Microorganisms in Cocultures and Monocultures: Aspergillus terreus and Streptomyces rimosus Warfare in Bioreactors.

The aim of this study was to quantitatively characterize the morphology of the filamentous microorganisms Aspergillus terreus ATCC 20542 and Streptomyces rimosus ATCC 10970, cocultivated in stirred tank bioreactors, and to characterize their mutual influence with the use of quantitative image analysis. Three distinct coculture initiation strategies were applied: preculture versus preculture, spores versus spores and preculture versus preculture with time delay for one of the species. Bioreactor cocultures were accompanied by parallel monoculture controls. The results recorded for the mono- and cocultures were compared in order to investigate the effect of cocultivation on the morphological evolution of A. terreus and S. rimosus. Morphology-related observations were also confronted with the analysis of secondary metabolism. The morphology of the two studied filamentous species strictly depended on the applied coculture initiation strategy. In the cocultures initiated by the simultaneous inoculation, S. rimosus gained domination or advance over A. terreus. The latter microorganism dominated only in these experiments in which S. rimosus was introduced with a delay.

Metabolic modelling of syntrophic-like growth of a 1,3-propanediol producer, Clostridium butyricum, and a methanogenic archeon, Methanosarcina mazei, under anaerobic conditions.

Clostridium butyricum can convert glycerol into 1,3-propanediol, thereby generating unfortunately a high amount of acetate, formate and butyrate as inhibiting by-products. We have proposed a novel mixed culture comprising C. butyricum and a methane bacterium, Methanosarcina mazei, to relieve the inhibition and to utilise the by-products for energy production. In order to examine the efficiency of such a mixed culture, metabolic modelling of the culture system was performed in this work. The metabolic networks for the organisms were reconstructed from genomic and physiological data. Several scenarios were analysed to examine the preference of M. mazei in scavenging acetate and formate under conditions of different substrate availability, including methanol as a co-substrate, since it may exist in glycerol solution from biodiesel production. The calculations revealed that if methanol is present, the methane production can increase by 130%. M. mazei can scavenge over 70% of the acetate secreted by C. butyricum.

Confrontation between Penicillium rubens and Aspergillus terreus: Investigating the production of fungal secondary metabolites in submerged co-cultures.

The production of secondary metabolites in the submerged co-cultures of Penicillium rubens Wisconsin 54-1255 and Aspergillus terreus ATCC 20542 was evaluated. The biosynthetic capabilities of the two strains were compared in a set of diverse liquid media that differed with respect to the initial levels of glucose, lactose and yeast extract, contained carrot juice or vegetable/turkey puree as additional nutrient sources or were supplemented with phenylacetic acid, the side-chain precursor of penicillin G. The main goal of the study was to investigate the interactions between A. terreus and P. rubens that might contribute to the changes of secondary metabolite titers. Briefly, the biosynthesis of octaketide metabolites (+)-geodin and asterric acid was visibly enhanced as a result of replacing the conventional monocultures with the co-culture systems, but solely in the media containing not more than 5 g L-1 of yeast extract. By contrast, no marked enhancement was observed with respect to the biosynthesis of penicillin G, lovastatin, chrysogine, 4a,5-dihydromevinolinic acid and 3α-hydroxy-3,5-dihydromonacolin L acid. It was shown that the relationships between medium composition and product titers were clearly different in monoculture variants than in the corresponding co-cultures. Finally, it was demonstrated that the utilization of penicillin precursors by P. rubens can be blocked under the conditions of co-cultivation.

Application of Aluminum Oxide Nanoparticles in Aspergillus terreus Cultivations: Evaluating the Effects on Lovastatin Production and Fungal Morphology.

Aluminum oxide nanoparticles were supplemented to Aspergillus terreus ATCC 20542 precultures and the outcomes of the process were evaluated relative to the results of microparticle-enhanced and standard cultivations. The selected morphological parameters of fungal pellets (projected area, elongation, convexity, and shape factor) were monitored throughout the experiment, together with biomass, lactose, and lovastatin concentration. The qualitative and quantitative chemical analysis was performed with the use of liquid chromatography coupled with high resolution mass spectrometry. The results of the study indicated that the application of nanoparticles was indeed associated with morphological consequences, most notably the decreased pellet size. However, it turned out that the term "nanoparticle-enhanced cultivation" could not be used in the context of lovastatin production, as no marked increase of product titer was observed in nanoparticle-influenced variants relative to standard and microparticle-enhanced cultivation. In addition, the concentration of biomass in the nanoparticle-influenced runs was relatively low. Comparative analysis of total ion chromatograms revealed the presence of a molecule of unknown structure that could be detected solely in broths from standard and microparticle-containing cultures. This study represents the first evaluation of nanoparticles as the tools of morphological engineering aimed at enhanced lovastatin biosynthesis in A. terreus cultures.