Cloning and characterization of monacolin K biosynthetic gene cluster from Monascus pilosus

The biosynthetic logic and enzymatic machinery of approved fungi-derived pharmaceuticals and agricultural biopesticides

Covering: 2000 to 2023The kingdom Fungi has become a remarkably valuable source of structurally complex natural products (NPs) with diverse bioactivities. Since the revolutionary discovery and application of the antibiotic penicillin from Penicillium, a number of fungi-derived NPs have been developed and approved into pharmaceuticals and pesticide agents using traditional "activity-guided" approaches. Although emerging genome mining algorithms and surrogate expression hosts have brought revolutionary approaches to NP discovery, the time and costs involved in developing these into new drugs can still be prohibitively high. Therefore, it is essential to maximize the utility of existing drugs by rational design and systematic production of new chemical structures based on these drugs by synthetic biology. To this purpose, there have been great advances in characterizing the diversified biosynthetic gene clusters associated with the well-known drugs and in understanding the biosynthesis logic mechanisms and enzymatic transformation processes involved in their production. We describe advances made in the heterogeneous reconstruction of complex NP scaffolds using fungal polyketide synthases (PKSs), non-ribosomal peptide synthetases (NRPSs), PKS/NRPS hybrids, terpenoids, and indole alkaloids and also discuss mechanistic insights into metabolic engineering, pathway reprogramming, and cell factory development. Moreover, we suggest pathways for expanding access to the fungal chemical repertoire by biosynthesis of representative family members via common platform intermediates and through the rational manipulation of natural biosynthetic machineries for drug discovery.

Histone lysine methyltransferases MpDot1 and MpSet9 are involved in the production of lovastatin and MonAzPs by histone crosstalk modification

Increasing data suggested that histone methylation modification plays an important role in regulating biosynthesis of secondary metabolites (SMs). Monascus spp. have been applied to produce hypolipidemic drug lovastatin (also called monacolin K, MK) and edible Monascus-type azaphilone pigments (MonAzPs). However, little is known about how histone methylation regulates MK and MonAzPs. In this study, we constructed H3K9 methyltransferase deletion strain ΔMpDot1 and H4K20 methyltransferase deletion strain ΔMpSet9 using Monascus pilosus MS-1 as the parent. The result showed that deletion of MpDot1 reduced the production of MK and MonAzPs, and deletion of MpSet9 increased MonAzPs production. Real-time quantitative PCR (RT-qPCR) showed inactivation of mpdot1 and mpset9 disturbed the expression of genes responsible for the biosynthesis of MK and MonAzPs. Western blot suggested that deletion of MpDot1 reduced H3K79me and H4K16ac, and deletion of MpSet9 decreased H4K20me3 and increased H4pan acetylation. Chromatin immunoprecipitation coupled with quantitative PCR (ChIP-qPCR) showed ΔMpDot1 strain and ΔMpSet9 strain reduced the enrichment of H3K79me2 and H4K20me3 in the promoter regions of key genes for MK and MonAzPs biosynthesis, respectively. These results suggested that MpDot1 and MpSet9 affected the synthesis of SMs by regulating gene transcription and histone crosstalk, providing alternative approach for regulation of lovastatin and MonAzPs.

Biosynthesis of the Isocoumarin Derivatives Fusamarins is Mediated by the PKS8 Gene Cluster in Fusarium

Fusarium mangiferae causes the mango malformation disease (MMD) on young mango trees and seedlings resulting in economically significant crop losses. In addition, F. mangiferae produces a vast array of secondary metabolites (SMs), including mycotoxins that may contaminate the harvest. Their production is tightly regulated at the transcriptional level. Here, we show that lack of the H3 K9-specific histone methyltransferase, FmKmt1, influences the expression of the F. mangiferae polyketide synthase (PKS) 8 (FmPKS8), a so far cryptic PKS. By a combination of reverse genetics, untargeted metabolomics, bioinformatics and chemical analyses including structural elucidation, we determined the FmPKS8 biosynthetic gene cluster (BGC) and linked its activity to the production of fusamarins (FMN), which can be structurally classified as dihydroisocoumarins. Functional characterization of the four FMN cluster genes shed light on the biosynthetic pathway. Cytotoxicity assays revealed moderate toxicities with IC50 values between 1 and 50 μM depending on the compound.

Computer-aided, resistance gene-guided genome mining for proteasome and HMG-CoA reductase inhibitors

Secondary metabolites (SMs) are biologically active small molecules, many of which are medically valuable. Fungal genomes contain vast numbers of SM biosynthetic gene clusters (BGCs) with unknown products, suggesting that huge numbers of valuable SMs remain to be discovered. It is challenging, however, to identify SM BGCs, among the millions present in fungi, that produce useful compounds. One solution is resistance gene-guided genome mining, which takes advantage of the fact that some BGCs contain a gene encoding a resistant version of the protein targeted by the compound produced by the BGC. The bioinformatic signature of such BGCs is that they contain an allele of an essential gene with no SM biosynthetic function, and there is a second allele elsewhere in the genome. We have developed a computer-assisted approach to resistance gene-guided genome mining that allows users to query large databases for BGCs that putatively make compounds that have targets of therapeutic interest. Working with the MycoCosm genome database, we have applied this approach to look for SM BGCs that target the proteasome β6 subunit, the target of the proteasome inhibitor fellutamide B, or HMG-CoA reductase, the target of cholesterol reducing therapeutics such as lovastatin. Our approach proved effective, finding known fellutamide and lovastatin BGCs as well as fellutamide- and lovastatin-related BGCs with variations in the SM genes that suggest they may produce structural variants of fellutamides and lovastatin. Gratifyingly, we also found BGCs that are not closely related to lovastatin BGCs but putatively produce novel HMG-CoA reductase inhibitors.

ONE-SENTENCE SUMMARY

A new computer-assisted approach to resistance gene-directed genome mining is reported along with its use to identify fungal biosynthetic gene clusters that putatively produce proteasome and HMG-CoA reductase inhibitors.

Identification of the polyketide synthase gene responsible for the synthesis of tanzawaic acids in Penicillium steckii IBWF104-06

Microorganisms have been used as biological control agents (BCAs) in agriculture for a long time, but their importance has increased dramatically over the last few years. The Penicillium steckii IBWF104-06 strain has presented strong BCA activity in greenhouse experiments performed against phytopathogenic fungi and oomycetes. P. steckii strains generally produce different antifungal tanzawaic acids; interesting compounds known to be catalyzed by polyketide synthetases in other fungi. Since the decalin structure is characteristic for tanzawaic acids, two polyketide synthase genes (PsPKS1 and PsPKS2) were selected for further analysis, which have similarity in sequence and gene cluster structure with genes that are known to be responsible for the biosynthesis of decalin-containing compounds. Subsequently, gene-inactivation mutants of both PsPKS1 and PsPKS2 have been generated. It was found, that the ΔPspks1 mutant cannot produce tanzawaic acids any more, whereas reintegration of the original PsPKS1 gene into the genome of ΔPspks1 reestablished tanzawaic acid production. The mutant ΔPspks2 is not altered in tanzawaic acids production. Interestingly, both mutants ΔPsPKS1 and ΔPsPKS2 still display strong BCA activity, indicating that the mechanism of action is not related to the production of tanzawaic acids.

Identification of the high-yield monacolin K strain from Monascus spp. and its submerged fermentation using different medicinal plants

BACKGROUND

Medical plants confer various benefits to human health and their bioconversion through microbial fermentation can increase efficacy, reduce toxicity, conserve resources and produce new chemical components. In this study, the cholesterol-lowering monacolin K genes and content produced by Monascus species were identified. The high-yield monacolin K strain further fermented with various medicinal plants. The antioxidant and anti-inflammatory activities, red pigment and monacolin K content, total phenolic content, and metabolites in the fermented products were analyzed.

RESULTS

Monacolin K was detected in Monascus pilosus (BCRC 38072), and Monascus ruber (BCRC 31533, 31523, 31534, 31535, and 33323). It responded to the highly homologous mokA and mokE genes encoding polyketide synthase and dehydrogenase. The high-yield monacolin K strain, M. ruber BCRC 31535, was used for fermentation with various medicinal plants. A positive relationship between the antioxidant capacity and total phenol content of the fermented products was observed after 60 days of fermentation, and both declined after 120 days of fermentation. By contrast, red pigment and monacolin K accumulated over time during fermentation, and the highest monacolin K content was observed in the fermentation of Glycyrrhiza uralensis, as confirmed by RT-qPCR. Moreover, Monascus-fermented medicinal plants including Paeonia lactiflora, Alpinia oxyphylla, G. uralensis, and rice were not cytotoxic. Only the product of Monascus-fermented G. uralensis significantly exhibited the anti-inflammatory capacity in a dose-dependent manner in lipopolysaccharide-induced Raw264.7 cells. The metabolites of G. uralensis with and without fermentation (60 days) were compared by LC/MS. 2,3-Dihydroxybenzoic acid, 3,4-dihydroxyphenylglycol, and 3-amino-4-hydroxybenzoate were considered to enhance the antioxidant and anti-inflammatory ability.

CONCLUSIONS

Given that highly homologous monacolin K and citrinin genes can be observed in Monascus spp., monacolin K produced by Monascus species without citrinin genes can be detected through the complementary methods of PCR and HPLC. In addition, the optimal fermentation time was important to the acquisition of antioxidants, red pigment and monacolin K. These bioactive substances were significantly affected by medicinal plants over fermentation time. Consequently, Monascus-fermented G. uralensis had a broad spectrum of biological activities.

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.

Promotion of monacolin K production in Monascus extractive fermentation: the variation in fungal morphology and in the expression levels of biosynthetic gene clusters

BACKGROUND

Monacolin K, an important secondary metabolite of Monascus, possesses a cholesterol-lowering effect and is widely used in the manufacture of antihypertensive drugs. In the present study, we constructed an extractive fermentation system by adding non-ionic surfactant and acquired a high monacolin K yield. The mechanism was determined by examining both cell morphology and the transcription levels of the related mokA-I genes in the monacolin K biosynthetic gene cluster.

RESULTS

The monacolin K yield was effectively increased to 539.59 mg L^-1 during extraction, which was an increase of 386.16% compared to that in the control group fermentation. The non-ionic surfactant showed good biocompatibility with Monascus. Electron scanning microscopy revealed alterations in the morphology of Monascus. The loosened mycelial structure and increased number of cell surface wrinkles were found to be related to the increased cell-membrane permeability and extracellular accumulation of monacolin K. Gene expression levels were measured via a quantitative reverse transciptase-polymerase chain reaction. By contrast, in the control group, mokA, mokB, mokC, mokD and mokF showed higher-level and longer-term expression in the extractive fermentation group, whereas mokE and mokG did not present a similar trend. The expression levels of mokH and mokI, encoding a transcription factor and efflux pump, respectively, were also higher than the control levels.

CONCLUSION

The addition of a non-ionic surfactant to Monascus fermentation effectively increases the yield of monacolin K by transforming the fungus morphology and promoting the expression of monacolin K biosynthesis genes. © 2021 Society of Chemical Industry.

An overview on the biological activity and anti-cancer mechanism of lovastatin

Lovastatin, a secondary metabolite isolated from fungi, is often used as a representative drug to reduce blood lipid concentration and treat hypercholesterolemia. Its structure is similar to that of HMG-CoA. Lovastatin inhibits the binding of the substrate to HMG-CoA reductase, and strongly competes with HMG-CoA reductase (HMGR), thereby exerting a hypolipidemic effect. Further, its safety has been confirmed in vivo and in vitro. Lovastatin also has anti-inflammatory, anti-cancer, and neuroprotective effects. Therefore, the biological activity of lovastatin, especially its anti-cancer effect, has garnered research attention. Several in vitro studies have confirmed that lovastatin has a significant inhibitory effect on cancer cell viability in a variety of cancers (such as breast, liver, cervical, lung, and colon cancer). At the same time, lovastatin can also increase the sensitivity of some types of cancer cells to chemotherapeutic drugs and strengthen their therapeutic effect. Lovastatin inhibits cell proliferation and regulates cancer cell signaling pathways, thereby inducing apoptosis and cell cycle arrest. This article reviews the structure, biosynthetic pathways, and applications of lovastatin, focusing on the anti-cancer effects and mechanisms of action.

An overview on the biosynthesis and metabolic regulation of monacolin K/lovastatin

Lovastatin/monacolin K (MK) is used as a lipid lowering drug, due to its effective hypercholesterolemic properties, comparable to synthetic statins. Lovastatin's biosynthetic pathway and gene cluster composition have been studied in depth in Aspergillus terreus. Evidence shows that the MK biosynthetic pathway and gene cluster in Monascus sp. are similar to those of lovastatin in A. terreus. Currently, research efforts have been focusing on the metabolic regulation of MK/lovastatin synthesis, and the evidence shows that a combination of extracellular and intracellular factors is essential for proper MK/lovastatin metabolism. Here, we comprehensively review the research progress on MK/lovastatin biosynthetic pathways, its synthetic precursors and inducing substances and metabolic regulation, with a view to providing reference for future research on fungal metabolism regulation and metabolic engineering for MK/lovastatin production.

Production of Monacolin K in Monascus pilosus: Comparison between Industrial Strains and Analysis of Its Gene Clusters

Monascus pilosus strains are widely applied to yield a cholesterol synthesis inhibitor monacolin K (MK), also called lovastatin (LOV). However, the mechanism of MK production by M. pilosus strains is still unclear. In this study, we firstly confirmed four Monascus strains, MS-1, YDJ-1, YDJ-2, and K104061, isolated from commercial MK products as M. pilosus and compared their abilities to produce MK in solid-state and liquid-state cultures. Then, we sequenced and analyzed their genomes and MK biosynthetic gene clusters (BGCs). The results revealed that the MK yields of MS-1, YDJ-1, YDJ-2, and K104061 in solid-state cultures at 14 days were 6.13, 2.03, 1.72, and 0.76 mg/g, respectively; the intracellular and extracellular MK contents of MS-1, YDJ-1, YDJ-2, and K104061 in liquid-state cultures at 14 days reached 0.9 and 1.8 mg/g, 0.38 and 0.43 mg/g, 0.30 and 0.42 mg/g, and 0.31 and 0.76 mg/g, respectively. The genome sizes of the four M. pilosus strains were about 26 Mb, containing about 7000-8000 coding genes and one MK gene cluster. The MK BGCs of MS-1, YDJ-2, and K104061 contained 11 genes, and the MK BGC of YDJ-1 contained 9 genes. According to the literature search, there are few comparisons of gene clusters and related genes responsible for the synthesis of LOV and MK. We also compared the LOV BGC in A. terreus with the MK BGCs in different species of Monascus spp., and the results revealed that although LOV and MK were the same substance, the genes responsible for the synthesis of MK were much less than those for LOV synthesis, and the gene functions were quite different. The current results laid a foundation to explore the mechanism of MK produced by Monascus spp. and compare the synthesis of LOV and MK.

Deep learning approaches for natural product discovery from plant endophytic microbiomes

Plant microbiomes are not only diverse, but also appear to host a vast pool of secondary metabolites holding great promise for bioactive natural products and drug discovery. Yet, most microbes within plants appear to be uncultivable, and for those that can be cultivated, their metabolic potential lies largely hidden through regulatory silencing of biosynthetic genes. The recent explosion of powerful interdisciplinary approaches, including multi-omics methods to address multi-trophic interactions and artificial intelligence-based computational approaches to infer distribution of function, together present a paradigm shift in high-throughput approaches to natural product discovery from plant-associated microbes. Arguably, the key to characterizing and harnessing this biochemical capacity depends on a novel, systematic approach to characterize the triggers that turn on secondary metabolite biosynthesis through molecular or genetic signals from the host plant, members of the rich 'in planta' community, or from the environment. This review explores breakthrough approaches for natural product discovery from plant microbiomes, emphasizing the promise of deep learning as a tool for endophyte bioprospecting, endophyte biochemical novelty prediction, and endophyte regulatory control. It concludes with a proposed pipeline to harness global databases (genomic, metabolomic, regulomic, and chemical) to uncover and unsilence desirable natural products.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1186/s40793-021-00375-0.

Mutational analysis of MpPhy reveals magnetoreception and photosensitivity involvement in secondary metabolites biosynthesis in Monascus purpureus

Light or low frequency magnetic field (LF-MF) as one of the cultivation environments affects secondary metabolites (SMs) production of M. purpureus. Phytochrome (Phy) is a hybrid histidine kinase possessing dual properties of photoreceptor and kinase to sense red and far-red light. The interaction effects of LF-MF and light on SMs of M. purpureus was investigated by knocking out the Phy-like gene in M. purpureus (MpPhy) by homologous recombination. A MpPhy-deletion (ΔMpPhy) strain produced less Monascus pigments (MPs) and monacolin K (mon K) than the wild-type (WT) strain and reduced citrinin production by 78.3% on 10th day but didn't affect the biomass. These results indicated that the MpPhy gene is involved in SMs biosynthesis of M. purpureus. MPs production in WT was decreased significantly when the inoculum was exposed to white/blue/green/red light (500 Lux). But it in ΔMpPhy was no significant difference when exposed to white/red light. The colony size of ΔMpPhy was smaller on potato dextrose agar media containing 0.01% SDS. These results indicated that the deletion of MpPhy gene affected the aerial hyphae and increased sensitivity to cell membrane stress but decreased sensitivity to red light. The inoculum of both WT and ΔMpPhy was exposure to the LF-MF (50 Hz). The accumulation of WT secondary metabolites was not changed, while SMs production of ΔMpPhy was significantly enhanced under exposed to 2.0 mT LF-MF. This indicated that the decrease of SMs caused by the deletion of MpPhy gene was restored by LF-MF. It revealed that there is a crosstalk between magnetoreception and photosensitivity.

Metabolomics Analysis of the Effect of Glutamic Acid on Monacolin K Synthesis in Monascus purpureus

Monacolin K is a secondary metabolite produced by Monascus with beneficial effects on health, including the ability to lower cholesterol. We previously showed that the yield of monacolin K was significantly improved when glutamic acid was added to the fermentation broth of Monascus purpureus M1. In this study, we analyzed M. purpureus in media with and without glutamic acid supplementation using a metabolomic profiling approach to identify key metabolites and metabolic pathway differences. A total of 817 differentially expressed metabolites were identified between the two fermentation broths on day 8 of fermentation. Pathway analysis of these metabolites using the KEGG database indicated overrepresentation of the citric acid cycle; biotin metabolism; and alanine, aspartate, and glutamate metabolic pathways. Six differentially expressed metabolites were found to be related to the citric acid cycle. The effect of citric acid as an exogenous additive on the synthesis of monacolin K was examined. These results provide technical support and a theoretical basis for further studies of the metabolic regulatory mechanisms underlying the beneficial effects of monacolin K and medium optimization, as well as genetic engineering of Monascus M1 for efficient monacolin K production.

Perspectives on Functional Red Mold Rice: Functional Ingredients, Production, and Application

Monacolin K (MK) is a secondary metabolite of the Monascus species that can inhibit cholesterol synthesis. Functional red mold rice (FRMR) is the fermentation product of Monascus spp., which is rich in MK. FRMR is usually employed to regulate serum cholesterol, especially for hypercholesterolemic patients who refuse statins or face statin intolerance. The present perspective summarized the bioactive components of FRMR and their functions. Subsequently, efficient strategies for FRMR production, future challenges of FRMR application, and possible directions were proposed. This perspective helps to understand the present situation and developmental prospects of FRMR.

Effects of Chinese medicines on monacolin K production and related genes transcription of Monascus ruber in red mold rice fermentation

Monacolin K (MK) is a secondary metabolite synthesized by polyketide synthases of Monascus spp. In this study, the combined supplementation of three medicines, including Citri Reticulatae Pericarpium (CRP), Fructus crataegi (FC), and Radix Angelicae Dahuricae (RAD), were mixed with nonglutinous rice and were optimized by response surface methodology to enhance the production of MK in fermented red mold rice (RMR). Under the optimum condition, MK production achieved 3.60 mg/g, which was 41.18% higher than RMR without medicines. The improved MK production was mainly caused by the up-regulated transcription level of mokA, mokB, mokF, mokH, mokI, and mplaeA. Meanwhile, the inhibitory effect of Poria cocos (PC) on MK production (only 0.436 mg/g) was caused by significantly down-regulated transcription of six tested genes. Therefore, this study is beneficial for better understanding of the possible mechanism of enhanced MK production by optimization of fermentation conditions.

Effects of Different G-Protein α-Subunits on Growth, Development and Secondary Metabolism of Monascus ruber M7

Strains of Monascus filamentous fungal species have been used to produce fermented foods in Asian countries, such as China, Japan, and The Korean Peninsula, for nearly 2,000 years. At present, their fermented products are widely used as food additives and nutraceutical supplements worldwide owing to their production of beneficial secondary metabolites. Heterotrimeric G-protein signaling pathways participate in regulating multiple biological processes in fungi. Previously, we identified three Monascus ruber M7 G-protein α subunits (Mga1–3) and demonstrated that Mga1 can regulate growth, reproduction and some secondary metabolites’ production. Here, we systematically analyzed and compared the roles of mga1–3 by combining single- and double-gene(s) knockouts and their transcriptomic data. First, mga2 and mga3 knock-out mutants and pairwise combinations of mga1–3 deletion strains were generated. Then the changes in growth, development and the main secondary metabolites, Monascus pigments and citrinin, in these mutants were systematically compared with M. ruber M7. Moreover, RNA-Seq analyses of these mutants were performed. All three Gα subunits worked together to regulate biological processes in M. ruber M7, with Mga1 playing a major role, while Mga2 and Mga3 playing supplemental roles. According to the existing literatures which we can find, gene knock-out mutants of the pairwise combination of mga1–3 and their transcriptome analysis are first reported in this study. The current results have clearly demonstrated the functional division of Mga1–3 in M. ruber M7, and could provide a deeper understanding of the effects of different Gα subunits on growth, development and secondary metabolism in other filamentous fungi.

A polyketide synthase gene cluster associated with the sexual reproductive cycle of the banana pathogen, Pseudocercospora fijiensis

Disease spread of Pseudocercospora fijiensis, causal agent of the black Sigatoka disease of banana, depends on ascospores produced through the sexual reproductive cycle. We used phylogenetic analysis to identify P. fijiensis homologs (PKS8-4 and Hybrid8-3) to the PKS4 polyketide synthases (PKS) from Neurospora crassa and Sordaria macrospora involved in sexual reproduction. These sequences also formed a clade with lovastatin, compactin, and betaenone-producing PKS sequences. Transcriptome analysis showed that both the P. fijiensis Hybrid8-3 and PKS8-4 genes have higher expression in infected leaf tissue compared to in culture. Domain analysis showed that PKS8-4 is more similar than Hybrid8-3 to PKS4. pPKS8-4:GFP transcriptional fusion transformants showed expression of GFP in flask-shaped structures in mycelial cultures as well as in crosses between compatible and incompatible mating types. Confocal microscopy confirmed expression in spermagonia in leaf substomatal cavities, consistent with a role in sexual reproduction. A disruption mutant of pks8-4 retained normal pathogenicity on banana, and no differences were observed in growth, conidial production, and spermagonia production. GC-MS profiling of the mutant and wild type did not identify differences in polyketide metabolites, but did identify changes in saturated fatty acid methyl esters and alkene and alkane derivatives. To our knowledge, this is the first report of a polyketide synthase pathway associated with spermagonia.

Overexpression of Monacolin K Biosynthesis Genes in the Monascus purpureus Azaphilone Polyketide Pathway

Monascus purpureus is an important food and drug microbial resource through the production of a variety of secondary metabolites, including monacolin K, a well-recognized cholesterol-lowering agent. However, the high production costs and naturally low contents of monacolin K have restricted its large-scale production. Thus, in this study we sought to improve the production of monacolin K in M. purpureus through overexpression of four genes ( mokC, mokD, mokE, and mokI). Four overexpression strains were successfully constructed by protoplast electric shock conversion, which resulted in a 234.3%, 220.8%, 89.5%, and 10% increase in the yield of monacolin K, respectively. The overexpression strains showed clear changes to the mycelium surface with obvious folds and the spores with depressions, whereas the pBC5 mycelium had a fuller structure with a flatter surface. Further investigation of these strains can provide the theoretical basis and technical support for the development of functional Monascus varieties.

Crystal structure of the condensation domain from lovastatin polyketide synthase

The highly reducing iterative polyketide synthases responsible for lovastatin biosynthesis contains a section homologous to condensation (CON) domain observed in nonribosomal peptide synthetases (NRPSs). In the present study, we expressed the isolated lovastatin CON domain and solved the crystal structure to 1.79 Å resolution. The overall structure shows similarity to canonical condensation domains of NRPSs, containing the N-terminal and C-terminal subdomains that resemble enzymes of chloramphenicol acetyltransferase family, whereas distinct structural features are observed at the active site. The acceptor entry of the substrate channel is blocked by a flexible loop, thereby preventing the loading of substrate for a new round of chain elongation. The mutation of conserved catalytic motif located at the midpoint of substrate channel agrees with the incapability of CON to catalyzed amide-bond formation. The structure helps to understand the function of CON in lovastatin biosynthesis.

iTRAQ-Based Quantitative Proteomic Analysis Reveals Changes in Metabolite Biosynthesis in Monascus purpureus in Response to a Low-Frequency Magnetic Field

Background: Low-frequency magnetic fields (LF-MFs) dampen the citrinin output by Monascus purpureus in fermentations. The influence of LF-MFs on biosynthesis by M. purpureus was evaluated at the protein level. Methods: Cultures were treated with a 1.6-mT MF from day 0 to day 2 of incubation, and secondary metabolite production was evaluated on the day 12 of incubation. All proteins were extracted from M. purpureus mycelia and subjected to isobaric tags for relative and absolute quantification (iTRAQ) labeling and subsequent liquid chromatography/mass spectrometry (LC-MS/MS) analysis on day 6 of fermentation. Results: There was no difference in biomass between the treated samples and the control. Citrinin production was 46.7% lower, and the yields of monacolin K and yellow, orange, and red pigment were 29.3%, 31.3%, 41.7%, and 40.3% higher, respectively, in the exposed samples compared to the control. Protein expression in M. purpureus under LF-MF treatment was quantified using iTRAQ technology. Of 2031 detected proteins, 205 were differentially expressed. The differentially-expressed proteins were subjected to Gene Ontology (GO) functional annotation and statistical analysis, which revealed that they mainly refer to biological metabolism, translation, antioxidant, transport and defense pathways. Among all the tagged proteins, emphasis was placed on the analysis of those involved in the synthesis of citrinin, pigment and monacolin K was emphasized. Conclusions: LF-MFs affected Monascus secondary metabolism at the protein level, and aggregate data for all the protein profiles in LF-MF-treated Monascus was obtained.

Genomics-driven discovery of a novel self-resistance mechanism in the echinocandin-producing fungus Pezicula radicicola

The echinocandins are antifungal lipopeptides targeting fungi via noncompetitive inhibition of the β-1,3-d-glucan synthase FKS1 subunit. A novel echinocandin resistance mechanism involving an auxiliary copy of FKS1 in echinocandin-producing fungus Pezicula radicicola NRRL 12192 was discovered. We sequenced the genome of NRRL 12192 and predicted two FKS1-encoding genes (prfks1n and prfks1a), rather than a single FKS1 gene typical of filamentous ascomycetes. The prfks1a gene sits immediately adjacent to an echinocandin (sporiofungin) gene cluster, which was confirmed by disruption of prnrps4 and abolishment of sporiofungin production. Disruption of prfks1a dramatically increased the strain's sensitivity to exogenous echinocandins. In the absence of echinocandins, transcription levels of prfks1a relative to β-tubulin in the wild type and in Δprnrps4 stains were similar. Moreover, prfks1a is consistently transcribed at low levels and is upregulated in the presence of exogenous echinocandin, but not during growth conditions promoting endogenous production of sporiofungin. Therefore, we conclude that prfks1a is primarily responsible for protecting the fungus against extracellular echinocandin toxicity. The presence of unclustered auxiliary copies of FKS1 with high similarity to prfks1a in two other echinocandin-producing strains suggests that this previously unrecognized resistance mechanism may be common in echinocandin-producing fungi of the family Dermataceae of the class Leotiomycetes.

Beneficial Effects of Monascus sp. KCCM 10093 Pigments and Derivatives: A Mini Review

The production of Monascus pigments and related byproducts, via microbial fermentation, has been broadly utilized as coloring by traditional food industries and as a natural textile dye. In addition to these traditional purposes, Monascus pigments have been recently favored for a variety of commercial and academic purposes. Pigments and derivatives formed during Monascus fermentation have pharmaceutical and clinical properties that can counteract common diseases, including obesity, type-2 diabetes, and cancer. Various research attempts have investigated the optimum conditions for this derived compound synthesis, as well as the still-unknown bio-functional effects. Recently, several studies were conducted using Monascus sp. KCCM 10093 and its derivatives. These experimental outcomes potentially reflect the bio-functional features of Monascus sp. KCCM 10093. However, no publication to date provides an overview of Monascus sp. KCCM 10093's unique metabolite products, functionalities, or biological pathways. In order to develop profitable commercial applications of Monascus sp. KCCM 10093, it is necessary not only to conduct continuous research, but also to systematically organize previous Monascus studies. The goals of this review are to investigate the current derivatives of Monascus sp. KCCM 10093 pigments-some of which have demonstrated newly-identified functionality-and the relevant uses of these molecules for pharmaceutical or nutraceutical purposes.

Glutamic acid promotes monacolin K production and monacolin K biosynthetic gene cluster expression in Monascus

This study investigated the effects of glutamic acid on production of monacolin K and expression of the monacolin K biosynthetic gene cluster. When Monascus M1 was grown in glutamic medium instead of in the original medium, monacolin K production increased from 48.4 to 215.4 mg l⁻¹, monacolin K production increased by 3.5 times. Glutamic acid enhanced monacolin K production by upregulating the expression of mokB-mokI; on day 8, the expression level of mokA tended to decrease by Reverse Transcription-polymerase Chain Reaction. Our findings demonstrated that mokA was not a key gene responsible for the quantity of monacolin K production in the presence of glutamic acid. Observation of Monascus mycelium morphology using Scanning Electron Microscope showed glutamic acid significantly increased the content of Monascus mycelium, altered the permeability of Monascus mycelium, enhanced secretion of monacolin K from the cell, and reduced the monacolin K content in Monascus mycelium, thereby enhancing monacolin K production.

Linoleic acid enhance the production of moncolin K and red pigments in Monascus ruber by activating mokH and mokA, and by accelerating cAMP-PkA pathway

Monacolin K, an inhibitor of HMG-CoA reductase, is a secondary metabolite synthesized by polyketide synthases (PKS) from Monascus ruber. The mokH gene encoding Zn(II)2Cys6 binding protein and mokA gene encoding polyketide synthase are presumed to activate monacolin K production. In this study, linoleic acid could be a quorum sensing signaling molecule to increase monacolin K production in the cyclic AMP(cAMP)-protein kinase A(PKA) signaling pathway. Analysis of the PKA activity and the cAMP concentration shows that linoleic acid could increase cAMP concentration and activate PKA. Analysis of the RT-qPCR products demonstrates that 256μM and 512μM linoleic acid can up-regulate mokH and mokA gene transcript levels. Especially with 512μM linoleic acid addition, linoleic acid increase 1.35 folds of monacolin K production, but 64μM linoleic acid increase 1.94 folds of red pigment production in Monascus ruber. These results show the cAMP-PkA pathway activity can up-regulate mokA and mokH gene, which enhance the yield of Monacolin K.

Effects of Additions of Monascus and Laccaic acid on the Color and Quality Properties of Nitrite-Free Emulsion Sausage during Refrigerated Storage

This effect of Monascus and Laccaic acid on the chemical composition, physical, texture and sensory properties of sausage were investigated during storage. Eight treatments (T) of sausage such as T1 (12 ppm sodium nitrite), while T2, T3, T4, T5, T6 and T7 were formulated with different ratios of Monascus/Laccaic acid: 63/7.0, 108/12, 135/15, 59.5/10.5, 102/18 and 127.5/22.5 ppm, respectively. The batch formulated without nitrite or Monascus and laccaic acid was served as control (C). The control sausages had higher pH values compared to the treated ones at 3, 10 and 28 d storage (p<0.05). After 10 d storage, the pH values decreased in treated sausage samples (p<0.05). The T1 and T4 presented the lowest yellowness and lightness values, respectively over the storage period. The redness values were increased as increasing Monascus and Laccaic acid amounts (T2-T4, T5-T7). The addition of Monascus and Laccaic acid had significantly higher hardness and springiness values (p<0.05) compared with the control in 3, 19 or 28 d storage. The results indicated that the addition of Monascus and Laccaic acid could improve the redness of the products.

Biologically Active Secondary Metabolites from the Fungi

Many Fungi have a well-developed secondary metabolism. The diversity of fungal species and the diversification of biosynthetic gene clusters underscores a nearly limitless potential for metabolic variation and an untapped resource for drug discovery and synthetic biology. Much of the ecological success of the filamentous fungi in colonizing the planet is owed to their ability to deploy their secondary metabolites in concert with their penetrative and absorptive mode of life. Fungal secondary metabolites exhibit biological activities that have been developed into life-saving medicines and agrochemicals. Toxic metabolites, known as mycotoxins, contaminate human and livestock food and indoor environments. Secondary metabolites are determinants of fungal diseases of humans, animals, and plants. Secondary metabolites exhibit a staggering variation in chemical structures and biological activities, yet their biosynthetic pathways share a number of key characteristics. The genes encoding cooperative steps of a biosynthetic pathway tend to be located contiguously on the chromosome in coregulated gene clusters. Advances in genome sequencing, computational tools, and analytical chemistry are enabling the rapid connection of gene clusters with their metabolic products. At least three fungal drug precursors, penicillin K and V, mycophenolic acid, and pleuromutilin, have been produced by synthetic reconstruction and expression of respective gene clusters in heterologous hosts. This review summarizes general aspects of fungal secondary metabolism and recent developments in our understanding of how and why fungi make secondary metabolites, how these molecules are produced, and how their biosynthetic genes are distributed across the Fungi. The breadth of fungal secondary metabolite diversity is highlighted by recent information on the biosynthesis of important fungus-derived metabolites that have contributed to human health and agriculture and that have negatively impacted crops, food distribution, and human environments.

Microbiota associated with the starter cultures and brewing process of traditional Hong Qu glutinous rice wine

Hong Qu glutinous rice wine (produced mainly in Fujian province, China) is a traditional alcoholic beverage, which is prepared by fermenting cooked rice using a starter containing Monascus purpureus. In this review, the microbial diversity of fermentation starters from Fujian province, including fungi, bacteria, and yeast, is analyzed in comparison with those of "nuruk" (a traditional starter for making alcoholic beverages in Korea). The bacterial organization of Hong Qu starters was vastly variable in species composition and dominated by Bacillus sp. Lactic acid bacteria were also found in some starters. In case of fungi, Monascus sp. was dominant, whereas non-Saccharomyces yeast such as Saccharomycopsis fibuligera was detected. The microorganisms found in the nuruk starter are, in general, not significantly diverse compared with those found in the Hong Qu starter, with the exception of Monascus sp.; however, Hong Qu and nuruk both contain their own unique microbiota, which are quite diverse from each other.

Mycotoxin monitoring for commercial foodstuffs in Taiwan

Mycotoxins are toxic food contaminants that are naturally produced by certain fungi. They induce negative effects on human health by making food unsafe for consumption. In this study, analyses were performed to determine the levels and incidence of aflatoxins (AFs) in peanut products, tree nuts, spices, and Coix seeds; ochratoxin A (OTA) in wheat and roasted coffee, as well as OTA and AFs in rice; and citrinin (CIT) in red yeast rice (RYR) products. A total of 712 samples from nine different food categories were collected between 2012 and 2013. The samples were analyzed over 2 years for AFs, OTA, and CIT by methods recommended by the Ministry of Health and Welfare. These official analytical methods were extensively validated in-house and through interlaboratory trials. The analytical values of suspected contaminated specimens were confirmed by liquid chromatography - tandem mass spectrometry analysis to identify the specific mycotoxin present in the sample. We show that 689 samples (96.8%) complied with the regulations set by the Ministry of Health and Welfare. AFs were found in four peanut-candy products, one peanut-flour product, one pistachio product, one Sichuan-pepper product, and one Coix seed product. All had exceeded the maximum levels of 15 parts per billion for peanut and 10 parts per billion for other food products. Furthermore, 14 RYR samples contained CIT above 5 parts per million, and one RYR tablet exceeded the maximum amount allowed. Instances of AFs in substandard Sichuan pepper and Coix seeds were first detected in Taiwan. Measures were taken by the relevant authorities to remove substandard products from the market in order to decrease consumer exposure to mycotoxin. Border control measures were applied to importing food commodities with a higher risk of mycotoxin contamination, such as peanut, Sichuan pepper, and RYR products. Declining trends were observed in the noncompliance rate of AFs in peanut products, as well as that of CIT in RYR raw materials monitored from 2010 to 2013.

Heterologous expression of MlcE in Saccharomyces cerevisiae provides resistance to natural and semi-synthetic statins

Statins are inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A reductase, the key enzyme in cholesterol biosynthesis. Their extensive use in treatment and prevention of cardiovascular diseases placed statins among the best selling drugs. Construction of Saccharomyces cerevisiae cell factory for the production of high concentrations of natural statins will require establishment of a non-destructive self-resistance mechanism to overcome the undesirable growth inhibition effects of statins. To establish active export of statins from yeast, and thereby detoxification, we integrated a putative efflux pump-encoding gene mlcE from the mevastatin-producing Penicillium citrinum into the S. cerevisiae genome. The resulting strain showed increased resistance to both natural statins (mevastatin and lovastatin) and semi-synthetic statin (simvastatin) when compared to the wild type strain. Expression of RFP-tagged mlcE showed that MlcE is localized to the yeast plasma and vacuolar membranes. We provide a possible engineering strategy for improvement of future yeast based production of natural and semi-synthetic statins.

Insights into Monascus biology at the genetic level

The genus of Monascus was nominated by van Tieghem in 1884, but its fermented product-red mold rice (RMR), namely red yeast rice, has been used as folk medicines, food colorants, and fermentation starters for more than thousands of years in oriental countries. Nowadays, RMR is widely developed as food supplements around the world due to its functional compounds such as monacolin K (MK, also called lovastatin) and γ-aminobutyric acid. But the usage of RMR also incurs controversy resulting from contamination of citrinin (a kind of mycotoxin) produced by some Monascus strains. In the past decade, it has made great progress to Monascus spp. at the genetic level with the application of molecular biology techniques to restrain the citrinin production and increase the yields of MK and pigment in RMR, as well as aid Monascus classification and phylogenesis. Up to now, hundreds of papers about Monascus molecular biology (MMB) have been published in the international primary journals. However, to our knowledge, there is no MMB review issued until now. In this review, current understanding of Monascus spp. from the view of molecular biology will be covered and insights into research areas that need to be further investigated will also be discussed.

Culture-based and sequence-based insights into biosynthesis of secondary metabolites by Aspergillus terreus ATCC 20542

Aspergillus terreus ATCC 20542 was cultivated in various culture media in order to activate its genome-encoded biosynthetic pathways and explore the secondary metabolic repertoire. In addition to mevinolinic acid (lovastatin) and its precursor monacolin L, a number of other secondary metabolites were found in the analyzed cultures, namely terreic acid, citrinin, (+)-geodin, terrein, and dehydrocurvularin. In contrast to previously described gene clusters responsible for production of lovastatin, monacolin L, (+)-geodin and dehydrocurvularin, the gene clusters of A. terreus associated with the formation of terreic acid, citrinin and terrein still await identification. Putative gene clusters potentially related to citrinin and terreic acid biosynthesis were suggested in the publicly available genome of A. terreus NIH 2624. The functions of putative genes in the previously identified cluster of (+)-geodin biosynthesis were predicted by confronting the annotation results with the proposed biosynthetic pathway and published biochemical studies on the underlying enzymes. Since there were no available data regarding genetic aspects of terrein biosynthesis, the candidate gene cluster potentially responsible for the production of terrein was not suggested.

Ku70 and ku80 null mutants improve the gene targeting frequency in Monascus ruber M7

Normally, gene targeting by homologous recombination occurs rarely during a transformation process since non-homologous recombination is predominant in filamentous fungi. In our previous researches, the average gene replacement frequency (GRF) in Monascus ruber M7 was as low as 15 %. To develop a highly efficient gene targeting system for M. ruber M7, two M. ruber M7 null mutants of ku70 (MrΔku70) and ku80 (MrΔku80) were constructed which had no apparent defects in the development including vegetative growth, colony phenotype, microscopic morphology and spore yield compared with M. ruber M7. In addition, the production of some significant secondary metabolites such as pigments and citrinin had no differences between the two disruptants and the wild-type strain. Further results revealed that the GRFs of triA (encoding a putative acetyltransferase) were 42.2 % and 61.5 % in the MrΔku70 and MrΔku80 strains, respectively, while it was only about 20 % in M. ruber M7. Furthermore, GRFs of these two disruptants at other loci (the pigE, fmdS genes in MrΔku70 and the ku70 gene in MrΔku80) were investigated, and the results indicated that GRFs in the MrΔku70 strain and the MrΔku80 strain were doubled and tripled compared with that in M. ruber M7, respectively. Therefore, the ku70 and ku80 null mutants of M. ruber M7, especially the ku80-deleted strain, will be excellent hosts for efficient gene targeting.