Overexpression of global regulator LaeA increases secondary metabolite production in Monascus purpureus

Effective enhancement of the ability of Monascus pilosus to produce lipid-lowering compound Monacolin K via perturbation of metabolic flux and histone acetylation modification

Monacolin K (MK), also known as lovastatin, is a polyketide compound with the ability to reduce plasma cholesterol levels and many other bio-activities. Red yeast rice (also named Hongqu) rich in MK derived from Monascus fermentation has attracted widespread attention due to its excellent performance in reducing blood lipids. However, industrial Monascus fermentation suffers from the limitations such as low yield of MK, long fermentation period, and susceptibility to contamination. In this study, we firstly blocked the competitive pathway of MK biosynthesis to create polyketide synthase gene pigA (the key gene responsible for the biosynthesis of Monascus azaphilone pigments) deficient strain A1. Then, based on the strategies to increase precursor supply for MK biosynthesis, acetyl-CoA carboxylase gene acc overexpression strains C1 and C2 were constructed with WT and A1 as the parent, respectively. Finally, histone deacetylase gene hos2 overexpression strain H1 was constructed by perturbation of histone acetylation modification. HPLC detection revealed all these four strains significantly increased their abilities to produce MK. After 14 days of solid-state fermentation, the MK yields of strains A1, C1, C2, and H1 reached 2.03 g/100 g, 1.81 g/100 g, 2.45 g/100 g and 2.52 g/100 g, which increased by 28.5 %, 14.7 %, 43.9 % and 36.1 % compared to WT, respectively. RT-qPCR results showed that overexpression of hos2 significantly increased the expression level of almost all genes responsible for MK biosynthesis after 5-day growth. Overall, the abilities of these strains to produce MK has been greatly improved, and MK production period has been shortened to 14 days from 20 days, providing new approaches for efficient production of Hongqu rich in MK.

A water-soluble mycelium polysaccharide from Monascus pilosus: Extraction, structural characterization, immunomodulatory effect and yield enhanced by overexpression of UGE gene

Mycelium polysaccharide (MPP) from Monascus pilosus with the compositions of glucose, galactose, mannose, glucosamine hydrochloride, rhamnose and arabinose, was obtained using alkaline extracting, and subsequently three purified components (MPP-0, MPP-0.1 and MPP-0.3) were separated. The purity and extraction volume of the MPP-0.1 fraction surpassed those of the other two groups, thus warranting its selection for subsequent experimental investigations. The sample MPP-0.1, with an average molecular weight of 3.7776 × 104 Da, exhibited exceptional thermal stability up to 170 °C. The main glycosidic linkage pattern of MPP-0.1 was structured as→[4)-α-D-Glcp-(1]6 → 4)-α-D-Glcp-(1 → [2)-α-D-Manp-(1]5 → 2)-α-D-Manp-(1 → 5)-β-D-Galf-(1 → 3)-β-D-Galf (1 → 3)-β-D-Galf-(1 → 3)-β-D-Galf-(1→, and branched Glcp, Manp, Galf fragments were connected with the main chain through →4, 6)-α-D-Glcp-(1→, →2, 6)-α-D-Manp-(1 → and →3, 6)-β-D-Galf-(1→. Besides, the up-regulated levels of Nitric oxide (NO), Tumor necrosis factor-α (TNF-α), Interleukin-6 (IL-6), Interleukin-1β (IL-1β) and other pro-inflammatory cytokines along with increased phagocytic activity revealed that MPP-0.1 has significant immunomodulatory effect, and can significantly enhance the proliferation and activation of RAW264.7 cells. Finally, the gene UGE (UDP-glucose 4-epimerase) was overexpressed in M. pilosus to increase the MPP production. Results showed that the biomass of the recombinant strain exhibited a remarkable increase of approximately 62.56 ± 1.50 % compared to that of the parental strain, and the extraction yield of MPP increased significantly by 83.19 ± 4.56 %.

Involvement of LaeA and Velvet Proteins in Regulating the Production of Mycotoxins and Other Fungal Secondary Metabolites

Fungi are rich sources of secondary metabolites of agrochemical, pharmaceutical, and food importance, such as mycotoxins, antibiotics, and antitumor agents. Secondary metabolites play vital roles in fungal pathogenesis, growth and development, oxidative status modulation, and adaptation/resistance to various environmental stresses. LaeA contains an S-adenosylmethionine binding site and displays methyltransferase activity. The members of velvet proteins include VeA, VelB, VelC, VelD and VosA for each member with a velvet domain. LaeA and velvet proteins can form multimeric complexes such as VosA-VelB and VelB-VeA-LaeA. They belong to global regulators and are mainly impacted by light. One of their most important functions is to regulate gene expressions that are responsible for secondary metabolite biosynthesis. The aim of this mini-review is to represent the newest cognition of the biosynthetic regulation of mycotoxins and other fungal secondary metabolites by LaeA and velvet proteins. In most cases, LaeA and velvet proteins positively regulate production of fungal secondary metabolites. The regulated fungal species mainly belong to the toxigenic fungi from the genera of Alternaria, Aspergillus, Botrytis, Fusarium, Magnaporthe, Monascus, and Penicillium for the production of mycotoxins. We can control secondary metabolite production to inhibit the production of harmful mycotoxins while promoting the production of useful metabolites by global regulation of LaeA and velvet proteins in fungi. Furthermore, the regulation by LaeA and velvet proteins should be a practical strategy in activating silent biosynthetic gene clusters (BGCs) in fungi to obtain previously undiscovered metabolites.

Mutation Breeding of Monascus to Produce a High Yield of Orange Pigment and Low Citrinin Content Using the ARTP Method

Monascus is a filamentous fungus with a long history of application in China, which can produce a variety of secondary metabolites, including Monascus red pigments, Monascus orange pigments, Monascus yellow pigments, and citrinin. There is widespread attention being paid to natural pigments because of their safety. Among the many natural pigments, orange pigment has a wide range of applications because of its unique color, but current production levels in the orange pigment industry are limited to a certain extent due to the insufficiently wide range of sources and low production. In this study, the ARTP mutation was used to obtain a strain with high-yield orange pigment and low citrinin. The strain RS7 was obtained through two-step mutagenesis, and all three pigments were improved to different degrees. The color value of orange pigment was elevated from the original 108 U/mL to 180 U/mL, an increase of 66.7% compared to the original strain, and the citrinin content was reduced by 69%. The result of microscopic morphology showed that RS7 has more wrinkles and is more convex than the R1 strain, but there was little change between the two strains. Therefore, the ARTP mutation influenced the growth and the biosynthesis of pigments in Monascus. In addition, the conditions of ultrasonic extraction of Monascus pigments were optimized using the response surface, and the separation of pigments was achieved with the method of thin-layer chromatography. Pigment stability results showed that the temperature had no significant effect on orange pigment, while tea polyphenol could improve its stability. This study generated a strain with high-yielding orange pigment and could lay a foundation for the future application of Monascus orange pigment in the food industry.

Nucleic acid demethylase MpAlkB1 regulates the growth, development, and secondary metabolite biosynthesis in Monascus purpureus

Nucleic acid demethylases of α-ketoglutarate-dependent dioxygenase (AlkB) family can reversibly erase methyl adducts from nucleobases, thus dynamically regulating the methylation status of DNA/RNA and playing critical roles in multiple cellular processes. But little is known about AlkB demethylases in filamentous fungi so far. The present study reports that Monascus purpureus genomes contain a total of five MpAlkB genes. The MpAlkB1 gene was disrupted and complemented through homologous recombination strategy to analyze its biological functions in M. purpureus. MpAlkB1 knockout significantly accelerated the growth of strain, increased biomass, promoted sporulation and cleistothecia development, reduced the content of Monascus pigments (Mps), and strongly inhibited citrinin biosynthesis. The downregulated expression of the global regulator gene LaeA, and genes of Mps biosynthesis gene cluster (BGC) or citrinin BGC in MpAlkB1 disruption strain supported the pleiotropic trait changes caused by MpAlkB1 deletion. These results indicate that MpAlkB1-mediated demethylation of nucleic acid plays important roles in regulating the growth and development, and secondary metabolism in Monascus spp.

Unlocking fungal quorum sensing: Oxylipins and yeast interactions enhance secondary metabolism in monascus

Exploring the symbiotic potential between fungal and yeast species, this study investigates the co-cultivation dynamics of Monascus, a prolific producer of pharmacologically relevant secondary metabolites, and Wickerhamomyce anomalous. The collaborative interaction between these microorganisms catalyzed a substantial elevation in the biosynthesis of secondary metabolites, prominently Monacolin K and natural pigments. Central to our discoveries was the identification and enhanced production of oxylipins (13S-hydroxyoctadecadienoic acid，13S-HODE), putative quorum-sensing molecules, within the co-culture environment. Augmentation with exogenous oxylipins not only boosted Monacolin K production by over half but also mirrored morphological adaptations in Monascus, affecting both spores and mycelial structures. This augmentation was paralleled by a significant upregulation in the transcriptional activity of genes integral to the Monacolin K biosynthetic pathway, as well as genes implicated in pigment and spore formation. Through elucidating the interconnected roles of quorum sensing, G-protein-coupled receptors, and the G-protein-mediate signaling pathway, this study provides a comprehensive view of the molecular underpinnings facilitating these metabolic enhancements. Collectively, our findings illuminate the profound influence of Wickerhamomyces anomalous co-culture on Monascus purpureus, advocating for oxylipins as a pivotal quorum-sensing mechanism driving the observed symbiotic benefits.

Taurine-mediated gene transcription and cell membrane permeability reinforced co-production of bioethanol and Monascus azaphilone pigments for a newly isolated Monascus purpureus

BACKGROUND

Taurine, a semi-essential micronutrient, could be utilized as a sulfur source for some bacteria; however, little is known about its effect on the accumulation of fermentation products. Here, it investigated the effect of taurine on co-production of bioethanol and Monascus azaphilone pigments (MonAzPs) for a fungus.

RESULTS

A newly isolated fungus of 98.92% identity with Monascus purpureus co-produced 23.43 g/L bioethanol and 66.12, 78.01 and 62.37 U/mL red, yellow and orange MonAzPs for 3 d in synthetic medium (SM). Taurine enhanced bioethanol titer, ethanol productivity and ethanol yield at the maximum by 1.56, 1.58 and 1.60 times than those of the control in corn stover hydrolysates (CSH), and red, yellow and orange MonAzPs were raised by 1.24, 1.26 and 1.29 times, respectively. Taurine was consumed extremely small quantities for M. purpureus and its promotional effect was not universal for the other two biorefinery fermenting strains. Taurine intensified the gene transcription of glycolysis (glucokinase, phosphoglycerate mutase, enolase and alcohol dehydrogenase) and MonAzPs biosynthesis (serine hydrolases, C-11-ketoreductase, FAD-dependent monooxygenase, 4-O-acyltransferase, deacetylase, NAD(P)H-dependent oxidoredutase, FAD-dependent oxidoredutase, enoyl reductase and fatty acid synthase) through de novo RNA-Seq assays. Furthermore, taurine improved cell membrane permeability through changing cell membrane structure by microscopic imaging assays.

CONCLUSIONS

Taurine reinforced co-production of bioethanol and MonAzPs by increasing gene transcription level and cell membrane permeability for M. purpureus. This work would offer an innovative, efficient and taurine-based co-production system for mass accumulation of the value-added biofuels and biochemicals from lignocellulosic biomass.

Histone H2B lysine 122 and lysine 130, as the putative targets of Penicillium oxalicum LaeA, play important roles in asexual development, expression of secondary metabolite gene clusters, and extracellular glycoside hydrolase synthesis

Core histones in the nucleosome are subject to a wide variety of posttranslational modifications (PTMs), such as methylation, phosphorylation, ubiquitylation, and acetylation, all of which are crucial in shaping the structure of the chromatin and the expression of the target genes. A putative histone methyltransferase LaeA/Lae1, which is conserved in numerous filamentous fungi, functions as a global regulator of fungal growth, virulence, secondary metabolite formation, and the production of extracellular glycoside hydrolases (GHs). LaeA's direct histone targets, however, were not yet recognized. Previous research has shown that LaeA interacts with core histone H2B. Using S-adenosyl-L-methionine (SAM) as a methyl group donor and recombinant human histone H2B as the substrate, it was found that Penicillium oxalicum LaeA can transfer the methyl groups to the C-terminal lysine (K) 108 and K116 residues in vitro. The H2BK108 and H2BK116 sites on recombinant histone correspond to P. oxalicum H2BK122 and H2BK130, respectively. H2BK122A and H2BK130A, two mutants with histone H2B K122 or K130 mutation to alanine (A), were constructed in P. oxalicum. The mutants H2BK122A and H2BK130A demonstrated altered asexual development and decreased extracellular GH production, consistent with the findings of the laeA gene deletion strain (ΔlaeA). The transcriptome data showed that when compared to wild-type (WT) of P. oxalicum, 38 of the 47 differentially expressed (fold change ≥ 2, FDR ≤ 0.05) genes that encode extracellular GHs showed the same expression pattern in the three mutants ΔlaeA, H2BK122A, and H2BK130A. The four secondary metabolic gene clusters that considerably decreased expression in ΔlaeA also significantly decreased in H2BK122A or H2BK130A. The chromatin of promotor regions of the key cellulolytic genes cel7A/cbh1 and cel7B/eg1 compacted in the ΔlaeA, H2BK122A, and H2BK130A mutants, according to the results of chromatin accessibility real-time PCR (CHART-PCR). The chromatin accessibility index dropped. The histone binding pocket of the LaeA-methyltransf_23 domain is compatible with particular histone H2B peptides, providing appropriate electrostatic and steric compatibility to stabilize these peptides, according to molecular docking. The findings of the study demonstrate that H2BK122 and H2BK130, which are histone targets of P. oxalicum LaeA in vitro, are crucial for fungal conidiation, the expression of gene clusters encoding secondary metabolites, and the production of extracellular GHs.

Multiplex metabolic pathway engineering of Monascus pilosus enhances lovastatin production

Monascus sp. is an important food microbial resource with the production of cholesterol-lowering agent lovastatin and other healthy metabolites. However, the mycotoxin citrinin naturally produced by Monascus sp. and the insufficient productivity of lovastatin limit its large-scale use in food industry. The aim of this paper is to modify a lovastatin-producing strain Monascus pilosus GN-01 through metabolic engineering to obtain a citrinin-free M. pilosus strain with higher yield of lovastatin. The citrinin synthesis regulator gene ctnR was firstly disrupted to obtain GN-02 without citrinin production. Based on that, the lovastatin biosynthesis genes (mokC, mokD, mokE, mokF, mokH, mokI, and LaeA) were, respectively, overexpressed, and pigment-regulatory gene (pigR) was knocked out to improve lovastatin production. The results indicated ctnR inactivation effectively disrupted the citrinin release by M. pilosus GN-01. The overexpression of lovastatin biosynthesis genes and pigR knockout could lead higher contents of lovastatin, of which pigR knockout strain achieved 76.60% increase in the yield of lovastatin compared to GN-02. These studies suggest that such multiplex metabolic pathway engineering in M. pilosus GN-01 is promising for high lovastatin production by a safe strain for application in Monascus-related food. KEY POINTS: • Disruption of the regulator gene ctnR inhibited citrinin production of M. pilosus. • Synchronous overexpression of biosynthesis gene enhanced lovastatin production. • pigR knockout enhanced lovastatin of ΔctnR strain of M. pilosus.

AfLaeA, a Global Regulator of Mycelial Growth, Chlamydospore Production, Pathogenicity, Secondary Metabolism, and Energy Metabolism in the Nematode-Trapping Fungus Arthrobotrys flagrans

Arthrobotrys flagrans (Duddingtonia flagrans) is a typical nematode-trapping fungus which has been used for nematode biocontrol. The global regulator LaeA is widely distributed in filamentous fungi and plays a crucial role in secondary metabolism and development in addition to pathogenicity in fungal pathogens. In this study, the chromosome-level genome of A. flagrans CBS 565.50 was sequenced and homologous sequences of LaeA were identified in A. flagrans. A. flagrans LaeA (AfLaeA) knockout resulted in slower hyphal growth and a smoother hyphal surface. Importantly, deletion of AfLaeA resulted in the absence of chlamydospores and attenuated glycogen and lipid accumulation in hyphae. Similarly, disruption of the AfLaeA gene led to fewer traps and electron-dense bodies, lower protease activity, and a delay in capturing nematodes. The AfLaeA gene had a large effect on the secondary metabolism of A. flagrans, and both the deletion and overexpression of AfLaeA could yield new compounds, whereas some compounds were lost due to the absence of the AfLaeA. Protein-protein interactions between AfLaeA and another eight proteins were detected. Furthermore, transcriptome data analysis showed that 17.77% and 35.51% of the genes were influenced by the AfLaeA gene on days 3 and 7, respectively. AfLaeA gene deletion resulted in the higher expression level of the artA gene cluster, and multiple differentially expressed genes involved in glycogen and lipid synthesis and metabolism showed opposite expression patterns in wild-type and ΔAfLaeA strains. In summary, our results provide novel insights into the functions of AfLaeA in mycelial growth, chlamydospore production, pathogenicity, secondary metabolism, and energy metabolism in A. flagrans. IMPORTANCE The regulation of biological functions, such as the secondary metabolism, development, and pathogenicity of LaeA, has been reported in multiple fungi. But to date, no study on LaeA in nematode-trapping fungi has been reported. Moreover, it has not been investigated whether or not LaeA is involved in energy metabolism and chlamydospore formation has not been investigated. Especially in the formation mechanism of chlamydospores, several transcription factors and signaling pathways are involved in the production of chlamydospores, but the mechanism of chlamydospore formation from an epigenetic perspective has not been revealed. Concurrently, an understanding of protein-protein interactions will provide a broader perspective on the regulatory mechanism of AfLaeA in A. flagrans. This finding is critical for understanding the regulatory role of AfLaeA in the biocontrol fungus A. flagrans and establishes a foundation for developing high-efficiency nematode biocontrol agents.

Histone Acetyltransferase Rtt109 Regulates Development, Morphogenesis, and Citrinin Biosynthesis in Monascus purpureus

Histone acetyltransferase (HAT) has been reported to be pivotal for various physiological processes in many fungi. However, the functions that HAT Rtt109 perform in edible fungi Monascus and the underlying mechanism remains unclear. Here, we identified the rtt109 gene in Monascus, constructed the rtt109 knockout strain (Δrtt109) and its complementary strain (Δrtt109:com) by CRISPR/Cas9 methods, and functionally characterized the roles that Rtt109 play in Monascus. Deletion of rtt109 significantly reduced conidia formation and colony growth, whereas, it increased the yield of Monascus pigments (MPs) and citrinin (CTN). Further real-time quantitative PCR (RT-qPCR) analysis indicated that Rtt109 remarkably affected the transcriptional expression of key genes related to development, morphogenesis, and secondary metabolism of Monascus. Together, our results revealed the critical roles of HAT Rtt109 in Monascus, and enriched our current knowledge of the development and regulation of secondary metabolism in fungi, throwing light on restraining or eliminating citrinin in the development and industrial applications of Monascus.

-Improved natural food colorant production in the filamentous fungus Monascus ruber using CRISPR-based engineering

Monascus pigments have various food industry applications and are pharmacologically active. Genome sequencing-based clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9) technology has been implemented to increase pigment production in Monascus. To increase pigment production in M. ruber KACC46666, the CRISPR/Cas9 system was used to introduce mutations in two negative regulator genes (MpigI and MpigI'), among other genes involved in the Monascus pigment biosynthesis pathway. Dual single-guide RNAs were constructed to inactivate MpigI and MpigI'. After CRISPR/Cas9 inactivation, yellow, orange, and red pigment expression in the resulting △MpigI16-7 strain (among several Cas9-mediated mutants studied) was 2.5-, 12.4-, and 18.5-fold, respectively, higher than that in the wild-type strain. This study provides valuable information regarding CRISPR-guided metabolic engineering for natural colorant production.

Recent Advances in Chitin Biosynthesis Associated with the Morphology and Secondary Metabolite Synthesis of Filamentous Fungi in Submerged Fermentation

Metabolites produced by filamentous fungi are used extensively in the food and drug industries. With the development of the morphological engineering of filamentous fungi, numerous biotechnologies have been applied to alter the morphology of fungal mycelia and enhance the yields and productivity of target metabolites during submerged fermentation. Disruption of chitin biosynthesis can modify the cell growth and mycelial morphology of filamentous fungi and regulate the biosynthesis of metabolites during submerged fermentation. In this review, we present a comprehensive coverage of the categories and structures of the enzyme chitin synthase, chitin biosynthetic pathways, and the association between chitin biosynthesis and cell growth and metabolism in filamentous fungi. Through this review, we hope to increase awareness of the metabolic engineering of filamentous fungal morphology, provide insights into the molecular mechanisms of morphological control via chitin biosynthesis, and describe strategies for the application of morphological engineering to enhance the production of target metabolites in filamentous fungi during submerged fermentation.

Linoleic acid functions as a quorum-sensing molecule in Monascus purpureus-Saccharomyces cerevisiae co-culture

When Monascus purpureus was co-cultured with Saccharomyces cerevisiae, we noted significant changes in the secondary metabolism and morphological development of Monascus. In yeast co-culture, although the pH was not different from that of a control, the Monascus mycelial biomass increased during fermentation, and the Monacolin K yield was significantly enhanced (up to 58.87% higher). However, pigment production did not increase. Co-culture with S. cerevisiae significantly increased the expression levels of genes related to Monacolin K production (mokA-mokI), especially mokE, mokF, and mokG. Linoleic acid, that has been implicated in playing a regulating role in the secondary metabolism and morphology of Monascus, was hypothesized to be the effector. Linoleic acid was detected in the co-culture, and its levels changed during fermentation. Addition of linoleic acid increased Monacolin K production and caused similar morphological changes in Monascus spores and mycelia. Exogenous linoleic acid also significantly upregulated the transcription levels of all nine genes involved in the biosynthesis of Monacolin K (up to 69.50% higher), consistent with the enhanced Monacolin K yield. Taken together, our results showed the effect of S. cerevisiae co-culture on M. purpureus and suggested linoleic acid as a specific quorum-sensing molecule in Saccharomyces-Monascus co-culture.

Itaconic acid production is regulated by LaeA in Aspergillus pseudoterreus

The global regulator LaeA controls secondary metabolism in diverse Aspergillus species. Here we explored its role in regulation of itaconic acid production in Aspergillus pseudoterreus. To understand its role in regulating metabolism, we deleted and overexpressed laeA, and assessed the transcriptome, proteome, and secreted metabolome prior to and during initiation of phosphate limitation induced itaconic acid production. We found that secondary metabolite clusters, including the itaconic acid biosynthetic gene cluster, are regulated by laeA and that laeA is required for high yield production of itaconic acid. Overexpression of LaeA improves itaconic acid yield at the expense of biomass by increasing the expression of key biosynthetic pathway enzymes and attenuating the expression of genes involved in phosphate acquisition and scavenging. Increased yield was observed in optimized conditions as well as conditions containing excess nutrients that may be present in inexpensive sugar containing feedstocks such as excess phosphate or complex nutrient sources. This suggests that global regulators of metabolism may be useful targets for engineering metabolic flux that is robust to environmental heterogeneity.

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The Itaconic acid biosynthetic gene cluster is regulated by laeA.

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LaeA is required for production of itaconic acid.

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Overexpression of laeA attenuates genes involved in phosphate acquisition.

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Global regulator engineering increases robustness of itaconic acid production.

Global regulatory factor AaLaeA upregulates the production of antitumor substances in the endophytic fungus Alternaria alstroemeria

The global regulatory factor LaeA has been shown to be involved in the biosynthesis of secondary metabolites in various fungi. In a previous work, we isolated an endophytic fungus from Artemisia annua, and its extract had a significant inhibitory effect on the A549 cancer cell line. Phylogenetic analysis further identified the strain as Alternaria alstroemeria. Overexpression of AalaeA gene resulted in significantly increased antitumor activity of this strain's extract. The 3-(4, 5- dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide assay results showed that the inhibition rate of the AalaeA^OE29 mutant extract on A549 cancer cells was significantly higher than that of the WT extract, as the IC₅₀ decreased from 195.0 to 107.4 μg/ml, and the total apoptosis rate was enhanced. Overexpression of the AalaeA gene significantly increased the contents of myricetin, geraniol, ergosterol, and 18 other antitumor compounds as determined by metabolomic analysis. Transcriptomic analysis revealed significant changes in 95 genes in the mutant strain, including polyketide synthases, nonribosomal peptide synthases, cytochrome P450s, glycosyltransferases, acetyl-CoA acetyltransferases, and others. These results suggested that AaLaeA mediated the antitumor activity of the metabolites in A. alstroemeria by regulating multiple metabolic pathways.

Disruption of the Chitin Biosynthetic Pathway Results in Significant Changes in the Cell Growth Phenotypes and Biosynthesis of Secondary Metabolites of Monascus purpureus

In this study, the gene monascus-5162 from Monascus purpureus LQ-6, identified as chitin synthase gene VI (chs6), was knocked out to disrupt the chitin biosynthetic pathway and regulate the biosynthesis of Monascus pigments (MPs) and citrinin. The results showed that the aerial hyphae on a solid medium were short and sparse after the deletion of chs6 in M. purpureus LQ-6, significantly reducing the germination percentage of active spores to approximately 22%, but the colony diameter was almost unaffected. Additionally, the deletion of chs6 changed the mycelial morphology of M. purpureus LQ-6 during submerged fermentation and increased its sensitivity to environmental factors. MP and citrinin biosynthesis was dramatically inhibited in the recombinant strain. Furthermore, comparative transcriptome analysis revealed that the pathways related to spore development and growth, including the MAPK signaling pathway, chitin biosynthetic pathway, and regulatory factors LaeA and WetA genes, were significantly downregulated in the early phase of fermentation. The mRNA expression levels of genes in the cluster of secondary metabolites were significantly downregulated, especially those related to citrinin biosynthesis. This is the first detailed study to reveal that chs6 plays a vital role in regulating the cell growth and secondary metabolism of the Monascus genus.

Functional Roles of LaeA-like Genes in Fungal Growth, Cellulase Activity, and Secondary Metabolism in Pleurotus ostreatus

The global regulator LaeA plays crucial roles in morphological development and secondary metabolite biosynthesis in filamentous fungi. However, the functions of LaeA in basidiomycetes are less reported. The basidiomycete Pleurotus ostreatus is a well-known fungus used both in medicine and as food that produces polysaccharides and cellulolytic enzymes. In this study, we characterized three LaeA homologs (PoLaeA1, PoLaeA2, and PoLaeA3) in P. ostreatus. PoLaeA1 showed different expression patterns than PoLaeA2 and PoLaeA3 during different developmental stages. Silencing PoLaeA1 decreased the intracellular polysaccharide (IPS) content by approximately 28–30% and reduced intracellular ROS levels compared with those of the WT strain. However, silencing PoLaeA2 and PoLaeA3 decreased cellulase activity by 31–34% and 35–40%, respectively, and reduced the cytosolic Ca2+ content, compared with those of the WT strain. Further analysis showed that PoLaeA1 regulated IPS biosynthesis through intracellular ROS levels, whereas PoLaeA2 and PoLaeA3 regulated cellulase activity through intracellular Ca2+ signaling. Our results provide new insights into the regulation of polysaccharide biosynthesis and cellulase production in filamentous fungi.

Overexpression of llm1 Affects the Synthesis of Secondary Metabolites of Aspergillus cristatus

Putative methyltransferases are thought to be involved in the regulation of secondary metabolites in filamentous fungi. Here, we report the effects of overexpression of a predicted LaeA-like methyltransferase gene llm1 on the synthesis of secondary metabolites in Aspergillus cristatus. Our results revealed that overexpression of the gene llm1 in A. cristatus significantly hindered the production of conidia and enhanced sexual development, and reduced oxidative tolerance to hydrogen peroxide. Compared with the wild-type, the metabolic profile of the overexpression transformant was distinct, and the contents of multiple secondary metabolites were markedly increased, mainly including terpenoids and flavonoids, such as (S)-olEuropeic acid, gibberellin A62, gibberellin A95, ovalitenone, PD 98059, and 1-isomangostin. A total of 600 significantly differentially expressed genes (DEGs) were identified utilizing transcriptome sequencing, and the DEGs were predominantly enriched in transmembrane transport and secondary metabolism-related biological processes. In summary, the strategy of overexpressing global secondary metabolite regulators successfully activated the expression of secondary metabolite gene clusters, and the numerous secondary metabolites were greatly strengthened in A. cristatus. This study provides new insights into the in-depth exploitation and utilization of novel secondary metabolites of A. cristatus.

Gram-Level Production of Balanol through Regulatory Pathway and Medium Optimization in Herb Fungus Tolypocladium ophioglossoides

As a potential protein kinase C inhibitor, the fungus metabolite balanol has become more attractive in recent decades. In our previous work, we revealed its biosynthetic pathway through overexpression of the cluster-situated regulator gene blnR in Chinese herb fungus Tolypocladium ophioglossoides. However, information on the regulation of blnR is still largely unknown. In this study, we further investigated the regulation of balanol biosynthesis by BlnR through the analysis of affinity binding using EMSA and RNA-seq analysis. The results showed that BlnR positively regulates balanol biosynthesis through binding to all promoters of bln gene members, including its own promoter. Microscopic observation revealed blnR overexpression also affected spore development and hypha growth. Furthermore, RNA-seq analysis suggested that BlnR can regulate other genes outside of the balanol biosynthetic gene cluster, including those involved in conidiospore development. Finally, balanol production was further improved to 2187.39 mg/L using the optimized medium through statistical optimization based on response surface methodology.

Effects of mokF gene deletion and overexpression on the Monacolin K metabolism yields of Monascus purpureus

Monascus purpureus is a fungus known for producing various physiologically active secondary metabolites. Of these, Monacolin K, a compound with hypocholesterolemic effects, is controlled by the biosynthetic gene mokF. Here, mokF deletion and overexpression strains (F2 and C3, respectively) were constructed using genetic engineering and compared with the M. purpureus wild strain (M1). The results showed that Monacolin K production was reduced by 50.86% in F2 and increased by 74.19% in C3. Of the three strains, C3 showed the highest production of Monacolin K and the most abnormal morphology. In addition, mokF influenced the expression level of mokA-mokI and might play an important role in regulating the biosynthesis of secondary metabolites in M. purpureus. Overall, our study verified the function of mokF in M. purpureus using gene deletion and overexpression technology. KEY POINTS: • The deletion and overexpression strains of mokF gene were successfully constructed. • The deletion or overexpression of mokF gene directly affected Monacolin K production. •The mokF gene had little effect on Monascus pigments and cell biomass.

Effect of γ-Heptalactone on the Morphology and Production of Monascus Pigments and Monacolin K in Monascus purpureus

Monascus is used widely in Asian countries and produces various biologically active metabolites, such as Monascus pigments (MPs) and monacolin K (MK). In this study, the effect of γ-heptalactone on secondary metabolites and mycelial growth during Monascus purpureus M1 fermentation was investigated. After the addition of 50 μM γ-heptalactone, the yields of MPs (yellow, orange, and red) reached maxima, increased by 115.70, 141.52, and 100.88%, respectively. The 25 μM γ-heptalactone groups showed the highest yield of MK was increased by 62.38% compared with that of the control. Gene expression analysis showed that the relative expression levels of MPs synthesis genes (MpPKS5, MpFasA2, mppB, mppC, mppD, mppG, mpp7, and mppR1/R2) were significantly upregulated after γ-heptalactone treatment. The relative expression levels of MK synthesis genes (mokA, mokC, mokE, mokH, and mokI) were significantly affected. The mycelium samples treated with γ-heptalactone exhibited more folds and swelling than that in the samples of the control group. This study confirmed that the addition of γ-heptalactone has the potential to induce yields of MPs and MK, and promote the expression of biosynthesis genes, which may be related to the transformation of mycelial morphology in M. purpureus.

Comprehensive Guide to Extracting and Expressing Fungal Secondary Metabolites with Aspergillus fumigatus as a Case Study

Fungal secondary metabolites (SMs) have captured the interest of natural products researchers in academia and industry for decades. In recent years, the high rediscovery rate of previously characterized metabolites is making it increasingly difficult to uncover novel compounds. Additionally, the vast majority of fungal SMs reside in genetically intractable fungi or are silent under normal laboratory conditions in genetically tractable fungi. The fungal natural products community has broadly overcome these barriers by altering the physical growth conditions of the fungus and heterologous/homologous expression of biosynthetic gene cluster regulators or proteins. The protocols described here summarize vital methodologies needed when researching SM production in fungi. We also summarize the growth conditions, genetic backgrounds, and extraction protocols for every published SM in Aspergillus fumigatus, enabling readers to easily replicate the production of previously characterized SMs. Readers will also be equipped with the tools for developing their own strategy for expressing and extracting SMs from their given fungus or a suitable heterologous model system. © 2021 Wiley Periodicals LLC. Basic Protocol 1: Making glycerol stocks from spore suspensions Alternate Protocol 1: Creating glycerol stocks from non-sporulating filamentous fungi Basic Protocol 2: Activating spore-suspension glycerol stocks Basic Protocol 3: Extracting secondary metabolites from Aspergillus spp grown on solid medium Alternate Protocol 2: Extracting secondary metabolites from Aspergillus spp using ethyl acetate Alternate Protocol 3: High-volume metabolite extraction using ethyl acetate Alternate Protocol 4: Extracting secondary metabolites from Aspergillus spp in liquid medium Support Protocol: Creating an overlay culture Basic Protocol 4: Extracting DNA from filamentous fungi Basic Protocol 5: Creating a DNA construct with double-joint PCR Alternate Protocol 5: Creating a DNA construct with yeast recombineering Basic Protocol 6: Transformation of Aspergillus spp Basic Protocol 7: Co-culturing fungi and bacteria for extraction of secondary metabolites.

Heteroexpression of Aspergillus nidulans laeA in Marine-Derived Fungi Triggers Upregulation of Secondary Metabolite Biosynthetic Genes

Fungi are a prospective resource of bioactive compounds, but conventional methods of drug discovery are not effective enough to fully explore their metabolic potential. This study aimed to develop an easily attainable method to elicit the metabolic potential of fungi using Aspergillus nidulans laeA as a transcription regulation tool. In this study, functional analysis of Aspergillus nidulans laeA (AnLaeA) and Aspergillus sp. Z5 laeA (Az5LaeA) was done in the fungus Aspergillus sp. Z5. Heterologous AnLaeA-and native Az5LaeA-overexpression exhibited similar phenotypic effects and caused an increase in production of a bioactive compound diorcinol in Aspergillus sp. Z5, which proved the conserved function of this global regulator. In particular, heteroexpression of AnLaeA showed a significant impact on the expression of velvet complex genes, diorcinol synthesis-related genes, and different transcription factors (TFs). Moreover, heteroexpression of AnLaeA influenced the whole genome gene expression of Aspergillus sp. Z5 and triggered the upregulation of many genes. Overall, these findings suggest that heteroexpression of AnLaeA in fungi serves as a simple and easy method to explore their metabolic potential. In relation to this, AnLaeA was overexpressed in the fungus Penicillium sp. LC1-4, which resulted in increased production of quinolactacin A.

Requirement of LaeA for sporulation, pigmentation and secondary metabolism in Chaetomium globosum

The global regulator LaeA has been confirmed to govern the production of secondary metabolites in fungi. Herein, we examined the role of LaeA in Chaetomium globosum. Similarly as observed in other filamentous, CgLaeA had a significant effect on the secondary metabolism. The ΔCglaeA mutant strain did not exhibit chaetoglobosin A, whereas its production was restored in the CglaeAC strain. In addition, CglaeA overexpression led to an increase in chaetoglobosin A production. Transcriptional examination of the mutants indicated that CgLaeA positively regulated the expression of pathway-specific transcription factor CgcheR, while another global regulator CgvelB was negatively regulated by CgLaeA. Furthermore, CgLaeA also affected the morphological phenotypes of fungi. The ΔCglaeA mutant strains exhibited decreased sporulation and pigmentation compared with the wild-type strain, whereas the phenotypes were restored in the CglaeAC strain. Moreover, OE::CglaeA exhibited increased levels of sporulation and pigmentation. Moreover, inhibition activity against phytopathogenic fungi affected by decreased mycotoxin production of the ΔCglaeA mutant strain.