Effects of the sporulation conditions on the lovastatin production by Aspergillus terreus

Screening and genetic engineering of marine-derived Aspergillus terreus for high-efficient production of lovastatin

BACKGROUND

Lovastatin has widespread applications thanks to its multiple pharmacological effects. Fermentation by filamentous fungi represents the major way of lovastatin production. However, the current lovastatin productivity by fungal fermentation is limited and needs to be improved.

RESULTS

In this study, the lovastatin-producing strains of Aspergillus terreus from marine environment were screened, and their lovastatin productions were further improved by genetic engineering. Five strains of A. terreus were isolated from various marine environments. Their secondary metabolites were profiled by metabolomics analysis using Ultra Performance Liquid Chromatography-Mass spectrometry (UPLC-MS) with Global Natural Products Social Molecular Networking (GNPS), revealing that the production of secondary metabolites was variable among different strains. Remarkably, the strain of A. terreus MJ106 could principally biosynthesize the target drug lovastatin, which was confirmed by High Performance Liquid Chromatography (HPLC) and gene expression analysis. By one-factor experiment, lactose was found to be the best carbon source for A. terreus MJ106 to produce lovastatin. To improve the lovastatin titer in A. terreus MJ106, genetic engineering was applied to this strain. Firstly, a series of strong promoters was identified by transcriptomic and green fluorescent protein reporter analysis. Then, three selected strong promoters were used to overexpress the transcription factor gene lovE encoding the major transactivator for lov gene cluster expression. The results revealed that compared to A. terreus MJ106, all lovE over-expression mutants exhibited significantly more production of lovastatin and higher gene expression. One of them, LovE-b19, showed the highest lovastatin productivity at a titer of 1512 mg/L, which represents the highest production level reported in A. terreus.

CONCLUSION

Our data suggested that combination of strain screen and genetic engineering represents a powerful tool for improving the productivity of fungal secondary metabolites, which could be adopted for large-scale production of lovastatin in marine-derived A. terreus.

Exploitation of Sugarcane Bagasse and Environmentally Sustainable Production, Purification, Characterization, and Application of Lovastatin by Aspergillus terreus AUMC 15760 under Solid-State Conditions

Using the internal transcribed spacer (ITS) region for identification, three strains of Aspergillus terreus were identified and designated AUMC 15760, AUMC 15762, and AUMC 15763 for the Assiut University Mycological Centre culture collection. The ability of the three strains to manufacture lovastatin in solid-state fermentation (SSF) using wheat bran was assessed using gas chromatography-mass spectroscopy (GC-MS). The most potent strain was strain AUMC 15760, which was chosen to ferment nine types of lignocellulosic waste (barley bran, bean hay, date palm leaves, flax seeds, orange peels, rice straw, soy bean, sugarcane bagasse, and wheat bran), with sugarcane bagasse turning out to be the best substrate. After 10 days at pH 6.0 at 25 °C using sodium nitrate as the nitrogen source and a moisture content of 70%, the lovastatin output reached its maximum quantity (18.2 mg/g substrate). The medication was produced in lactone form as a white powder in its purest form using column chromatography. In-depth spectroscopy examination, including ¹H, ¹³C-NMR, HR-ESI-MS, optical density, and LC-MS/MS analysis, as well as a comparison of the physical and spectroscopic data with published data, were used to identify the medication. At an IC₅₀ of 69.536 ± 5.73 µM, the purified lovastatin displayed DPPH activity. Staphylococcus aureus and Staphylococcus epidermidis had MICs of 1.25 mg/mL, whereas Candida albicans and Candida glabrata had MICs of 2.5 mg/mL and 5.0 mg/mL, respectively, against pure lovastatin. As a component of sustainable development, this study offers a green (environmentally friendly) method for using sugarcane bagasse waste to produce valuable chemicals and value-added commodities.

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%.

New knowledge about the biosynthesis of lovastatin and its production by fermentation of Aspergillus terreus

Lovastatin, and its semisynthetic derivative simvastatine, has great medical and economic importance, besides great potential for other uses. In the last years, a deeper and more complex view of secondary metabolism regulation has emerged, with the incorporation of cluster-specific and global transcription factors, and their relation to signaling cascades, as well as the new level of epigenetic regulation. Recently, a new mechanism, which regulates lovastatin biosynthesis, at transcriptional level, has been discovered: reactive oxygen species (ROS) regulation; also new unexpected environmental stimuli have been identified, which induce the synthesis of lovastatin, like quorum sensing-type molecules and support stimuli. The present review describes this new panorama and uses this information, together with the knowledge on lovastatin biosynthesis and genomics, as the foundation to analyze literature on optimization of fermentation parameters and medium composition, and also to fully understand new strategies for strain genetic improvement. This new knowledge has been applied to the development of more effective culture media, with the addition of molecules like butyrolactone I, oxylipins, and spermidine, or with addition of ROS-generating molecules to increase internal ROS levels in the cell. It has also been applied to the development of new strategies to generate overproducing strains of Aspergillus terreus, including engineering of the cluster-specific transcription factor (lovE), global transcription factors like the ones implicated in ROS regulation (or even mitochondrial alternative respiration aox gen), or the global regulator LaeA. Moreover, there is potential to apply some of these findings to the development of novel unconventional production systems. KEY POINTS: • New findings in regulation of lovastatin biosynthesis, like ROS regulation. • Induction by unexpected stimuli: autoinducer molecules and support stimuli. • Recent reports on culture medium and process optimization from this stand point. • Applications to molecular genetic strain improvement methods and production systems.

The investigation of media components for optimal metabolite production of Aspergillus terreus ATCC 20542

PURPOSE

This study aimed to assess the effect of nitrogen, salt and pre-culture conditions on the production of lovastatin in A. terreus ATCC 20542.

METHODS

Different combinations of nitrogen sources, salts and pre-culture combinations were applied in the fermentation media and lovastatin yield was analysed chromatographically.

RESULT

The exclusion of MnSO₄ ·5H₂O, CuSO₄·5H₂O and FeCl₃·6H₂O were shown to significantly improve lovastatin production (282%), while KH₂PO₄, MgSO₄·7H₂O, and NaCl and ZnSO₄·7H₂O were indispensable for good lovastatin production. Simple nitrogen source (ammonia) was unfavourable for morphology, growth and lovastatin production. In contrast, yeast extract (complex nitrogen source) produced the highest lovastatin yield (25.52 mg/L), while powdered soybean favoured the production of co-metabolites ((+)-geodin and sulochrin). Intermediate lactose: yeast extract (5:4) ratio produced the optimal lovastatin yield (12.33 mg/L) during pre-culture, while high (5:2) or low (5:6) lactose to yeast extract ratio produced significantly lower lovastatin yield (7.98 mg/L and 9.12 mg/L, respectively). High spore concentration, up to 10⁷ spores/L was shown to be beneficial for lovastatin, but not for co-metabolite production, while higher spore age was shown to be beneficial for all of its metabolites.

CONCLUSION

The findings from these investigations could be used for future cultivation of A. terreus in the production of desired metabolites.

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.

Exploitation of Aspergillus terreus for the Production of Natural Statins

The fungus Aspergillus (A.) terreus has dominated the biological production of the “blockbuster” drugs known as statins. The statins are a class of drugs that inhibit HMG-CoA reductase and lead to lower cholesterol production. The statins were initially discovered in fungi and for many years fungi were the sole source for the statins. At present, novel chemically synthesised statins are produced as inspired by the naturally occurring statin molecules. The isolation of the natural statins, compactin, mevastatin and lovastatin from A. terreus represents one of the great achievements of industrial microbiology. Here we review the discovery of statins, along with strategies that have been applied to scale up their production by A. terreus strains. The strategies encompass many of the techniques available in industrial microbiology and include the optimization of media and fermentation conditions, the improvement of strains through classical mutagenesis, induced genetic manipulation and the use of statistical design.

Bioprocess Engineering Aspects of the Cultivation of a Lovastatin Producer Aspergillus terreus

The aim of this work is to review bioprocess engineering aspects of lovastatin (antihypercholesterolemia drug) production by Aspergillus terreus in the submerged culture in the bioreactors of various scale presented in the scientific literature since the nineties of the twentieth century. The key factor influencing the cultivation of any filamentous species is fungal morphology and that is why this aspect was treated as the starting point for further considerations. Fungal morphology is known to have an impact on the following issues connected with the cultivation of A. terreus reviewed in this article. These are broth viscosity in conjunction with non-Newtonian behaviour of the cultivation broths, and multistage oxygen transfer processes: from gas phase (air) to liquid phase (broth) and diffusion in the fungal agglomerates. The latest achievements concerning the controlling A. terreus morphology during lovastatin biosynthesis with the use of morphological engineering techniques were also reviewed. Last but not least, some attention was paid to the type of a bioreactor, its operational mode and kinetic modelling of lovastatin production by A. terreus.

Lovastatin production: From molecular basis to industrial process optimization

Lovastatin, composed of secondary metabolites produced by filamentous fungi, is the most frequently used drug for hypercholesterolemia treatment due to the fact that lovastatin is a competitive inhibitor of HMG-CoA reductase. Moreover, recent studies have shown several important applications for lovastatin including antimicrobial agents and treatments for cancers and bone diseases. Studies regarding the lovastatin biosynthetic pathway have also demonstrated that lovastatin is synthesized from two-chain reactions using acetate and malonyl-CoA as a substrate. It is also known that there are two key enzymes involved in the biosynthetic pathway called polyketide synthases (PKS). Those are characterized as multifunctional enzymes and are encoded by specific genes organized in clusters on the fungal genome. Since it is a secondary metabolite, cultivation process optimization for lovastatin biosynthesis has included nitrogen limitation and non-fermentable carbon sources such as lactose and glycerol. Additionally, the influences of temperature, pH, agitation/aeration, and particle and inoculum size on lovastatin production have been also described. Although many reviews have been published covering different aspects of lovastatin production, this review brings, for the first time, complete information about the genetic basis for lovastatin production, detection and quantification, strain screening and cultivation process optimization. Moreover, this review covers all the information available from patent databases covering each protected aspect during lovastatin bio-production.

Microbial production and biomedical applications of lovastatin

Lovastatin is a potent hypercholesterolemic drug used for lowering blood cholesterol. Lovastatin acts by competitively inhibiting the enzyme, 3-hydroxy-3-methylglutaryl coenzyme A reductase involved in the biosynthesis of cholesterol. Commercially lovastatin is produced by a variety of filamentous fungi including Penicillium species, Monascus ruber and Aspergillus terreus as a secondary metabolite. Production of lovastatin by fermentation decreases the production cost compared to costs of chemical synthesis. In recent years, lovastatin has also been reported as a potential therapeutic agent for the treatment of various types of tumors and also play a tremendous role in the regulation of the inflammatory and immune response, coagulation process, bone turnover, neovascularization, vascular tone, and arterial pressure. This review deals with the structure, biosynthesis, various modes of fermentation and applications of lovastatin.

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.

Response surface methodology for lovastatin production by Aspergillus terreus GD13 strain

A wild type Aspergillus terreus GD13 strain, chosen after extensive screening, was optimized for lovastatin production using statistical Box-Behnken design of experiments. The interactive effect of four process parameters, i.e. lactose and soybean meal, inoculum size (spore concentration) and age of the spore culture, on the production of lovastatin was evaluated employing response surface methodology (RSM). The model highlighted the positive effect of soybean meal concentration and inoculum level for achieving maximal level of lovastatin (1342 mg/l). The optimal fermentation conditions improved the lovastatin titre by 7.0-folds when compared to the titres obtained under unoptimized conditions.

A macrokinetic modelling of the biosynthesis of lovastatin by Aspergillus terreus

In this work a simple kinetic model to describe the biosynthesis of lovastatin by Aspergillus terreus ATCC 20542 was proposed. Several series of experiments were conducted at different media compositions. The concentrations of C- and N-sources were changed over a wide range and so were the initial biomass concentrations. From these runs the relationships ruling the substrates uptake, biomass and product formation were learnt. Lovastatin biosynthesis appeared to be partly growth associated. The inhibitive effect of organic nitrogen on lovastatin biosynthesis was found and lactose appeared to be an important limiting substrate in the formation of lovastatin. The parameters of the model were evaluated on the basis of the kinetic data obtained in the separate experiments made in triplicate at two chosen media compositions. Other results obtained at different media compositions were independent of the ones mentioned above and used for the verification of the model. The validity of the model was also examined for the lactose-fed fed-batch run. Finally, a sensitivity analysis of the model parameters was performed. The formulated model, although relatively simplified, described the experimental data quite well and could be regarded as the background for further attempts to mathematically describe the process of lovastatin biosynthesis.