Enhancing extracellular monascus pigment production in submerged fermentation with engineered microbial consortia

In this study, we investigated the impact of microbial interactions on Monascus pigment (MP) production. We established diverse microbial consortia involving Monascus purpureus and Lactobacillus fermentum. The addition of Lactobacillus fermentum (4% at 48 h) to the submerged fermentation of M. purpureus resulted in a significantly higher MP production compared to that achieved using the single-fermentation system. Co-cultivation with immobilized L. fermentum led to a remarkable increase of 59.18% in extracellular MP production, while mixed fermentation with free L. fermentum caused a significant decrease of 66.93% in intracellular MPs, contrasting with a marginal increase of 4.52% observed during co-cultivation with immobilized L. fermentum and the control group respectively. The findings indicate an evident enhancement in cell membrane permeability of M. purpureus when co-cultivated with immobilized L. fementum. Moreover, integrated transcriptomic and metabolomic analyses were conducted to elucidate the regulatory mechanisms underlying MP biosynthesis and secretion following inoculation with immobilized L. fementum, with specific emphasis on glycolysis, steroid biosynthesis, fatty acid biosynthesis, and energy metabolism.

The serine/threonine protein kinase MpSTE1 directly governs hyphal branching in Monascus spp

Monascus spp. are commercially important fungi due to their ability to produce beneficial secondary metabolites such as the cholesterol-lowering agent lovastatin and natural food colorants azaphilone pigments. Although hyphal branching intensively influenced the production of these secondary metabolites, the pivotal regulators of hyphal development in Monascus spp. remain unclear. To identify these important regulators, we developed an artificial intelligence (AI)-assisted image analysis tool for quantification of hyphae-branching and constructed a random T-DNA insertion library. High-throughput screening revealed that a STE kinase, MpSTE1, was considered as a key regulator of hyphal branching based on the hyphal phenotype. To further validate the role of MpSTE1, we generated an mpSTE1 gene knockout mutant, a complemented mutant, and an overexpression mutant (OE::mpSTE1). Microscopic observations revealed that overexpression of mpSTE1 led to a 63% increase in branch number while deletion of mpSTE1 reduced the hyphal branching by 68% compared to the wild-type strain. In flask cultures, the strain OE::mpSTE1 showed accelerated growth and glucose consumption. More importantly, the strain OE::mpSTE1 produced 9.2 mg/L lovastatin and 17.0 mg/L azaphilone pigments, respectively, 47.0% and 30.1% higher than those of the wild-type strain. Phosphoproteomic analysis revealed that MpSTE1 directly phosphorylated 7 downstream signal proteins involved in cell division, cytoskeletal organization, and signal transduction. To our best knowledge, MpSTE1 is reported as the first characterized regulator for tightly regulating the hyphal branching in Monascus spp. These findings significantly expanded current understanding of the signaling pathway governing the hyphal branching and development in Monascus spp. Furthermore, MpSTE1 and its analogs were demonstrated as promising targets for improving production of valuable secondary metabolites. KEY POINTS: • MpSTE1 is the first characterized regulator for tightly regulating hyphal branching • Overexpression of mpSTE1 significantly improves secondary metabolite production • A high-throughput image analysis tool was developed for counting hyphal branching.

Disruption of UDP-galactopyranose mutase expression: A novel strategy for regulation of galactomannan biosynthesis and monascus pigments secretion in Monascus purpureus M9

The impact of the cell wall structure of Monascus purpureus M9 on the secretion of extracellular monascus pigments (exMPs) was investigated. To modify the cell wall structure, UDP-galactopyranose mutase (GlfA) was knocked out using Agrobacterium-mediated transformation method, leading to a significant reduction in the Galf-based polysaccharide within the cell wall. Changes in mycelium morphology, sporogenesis, and the expression of relevant genes in M9 were also observed following the mutation. Regarding MPs secretion, a notable increase was observed in six types of exMPs (R1, R2, Y1, Y2, O1 and O2). Specifically, these exMPs exhibited enhancement of 1.33, 1.59, 0.8, 2.45, 2.89 and 4.03 times, respectively, compared to the wild-type strain. These findings suggest that the alteration of the cell wall structure could selectively influence the secretion of MPs in M9. The underlying mechanisms were also discussed. This research contributes new insights into the regulation of the synthesis and secretion of MPs in Monascus spp..

CRISPR/Cas9 system is a suitable gene targeting editing tool to filamentous fungus Monascus pilosus

Monascus pilosus has been used to produce lipid-lowering drugs rich in monacolin K (MK) for a long period. Genome mining reveals there are still many potential genes worth to be explored in this fungus. Thereby, efficient genetic manipulation tools will greatly accelerate this progress. In this study, we firstly developed the protocol to prepare protoplasts for recipient of CRISPR/Cas9 system. Subsequently, the vector and donor DNA were co-transformed into recipients (106 protoplasts/mL) to produce 60-80 transformants for one test. Three genes (mpclr4, mpdot1, and mplig4) related to DNA damage response (DDR) were selected to compare the gene replacement frequencies (GRFs) of Agrobacterium tumefaciens-mediated transformation (ATMT) and CRISPR/Cas9 gene editing system (CGES) in M. pilosus MS-1. The results revealed that GRF of CGES was approximately five times greater than that of ATMT, suggesting that CGES was superior to ATMT as a targeting gene editing tool in M. pilosus MS-1. The inactivation of mpclr4 promoted DDR via the non-homologous end-joining (NHEJ) and increased the tolerances to DNA damaging agents. The inactivation of mpdot1 blocked DDR and led to the reduced tolerances to DNA damaging agents. The inactivation of mplig4 mainly blocked the NHEJ pathway and led to obviously reduced tolerances to DNA damaging agents. The submerged fermentation showed that the ability to produce MK in strain Δmpclr4 was improved by 52.6% compared to the wild type. This study provides an idea for more effective exploration of gene functions in Monascus strains. KEY POINTS: • A protocol of high-quality protoplasts for CGES has been developed in M. pilosus. • The GRF of CGES was about five times that of ATMT in M. pilosus. • The yield of MK for Δmpclr4 was enhanced by 52.6% compared with the wild type.

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.

Role of histone H3K4 methyltransferase in regulating Monascus pigments production by red light-coupled magnetic field

Light, magnetic field, and methylation affected the growth and secondary metabolism of fungi. The regulation effect of the three factors on the growth and Monascus pigments (MPs) synthesis of Monascus purpureus was investigated in this study. 5-azacytidine (5-AzaC), DNA methylation inhibitor, was used to treat M. purpureus (wild-type, WT). Twenty micromolar 5-AzaC significantly promoted the growth, development, and MPs yield. Moreover, 250 lux red light and red light coupled magnetic field (RLCMF) significantly promoted the biomass. For WT, red light, and RLCMF significantly promoted MPs yield. But compared with red light treatment, only 0.2 mT RLCMF promoted the alcohol-soluble MPs yield. For histone H3K4 methyltransferase complex subunit Ash2 gene knockout strain (ΔAsh2), only 0.2 mT RLCMF significantly promoted water-soluble MPs yield. Yet red light, 1.0 and 0.2 mT RLCMF significantly promoted alcohol-soluble MPs yield. This indicated that methylation affected the MPs biosynthesis. Red light and weaker MF had a synergistic effect on the growth and MPs synthesis of ΔAsh2. This result was further confirmed by the expression of related genes. Therefore, histone H3K4 methyltransferase was involved in the regulation of the growth, development, and MPs synthesis of M. purpureus by the RLCMF.

Regulation of the pigment production by changing Cell morphology and gene expression of Monascus ruber in high-sugar synergistic high-salt stress fermentation

AIMS

Extreme environment of microbial fermentation is the focus of research, which provides new thinking for the production and application of Monascus pigments (MPs). In this work, the high-sugar synergistic high-salt stress fermentation (HSSF) of MPs was investigated.

METHODS AND RESULTS

The Monascus fungus grew well under HSSF conditions with 35 g L-1 NaCl and 150 g L-1 glucose, and the extracellular yellow pigment and intracellular orange pigment yield in HSSF was 98% and 43% higher than that in conventional fermentation, respectively. Moreover, the mycelial morphology was maintained in a better status with more branches and complete surface structure, indicating good biocatalytic activity for pigment synthesis. Four extracellular yellow pigments (Y1, Y2, Y3, and Y4) were transformed into each other, and ratio of the relative content of intracellular orange pigments to yellow pigments (O/Y) significantly (P < 0.05) changed. Moreover, the ratio of unsaturated fatty acids to saturated fatty acids (unsaturated/saturated) was significantly (P < 0.05) increased, indicating that the metabolism and secretion of intracellular and extracellular pigment might be regulated in HSSF. The pigment biosynthesis genes mppB, mppC, mppD, MpPKS5, and MpFasB2 were up-regulated, whereas the genes mppR1, mppR2, and mppE were down-regulated, suggesting that the gene expression to regulate pigment biosynthesis might be a dynamic change process in HSSF.

CONCLUSIONS

The HSSF system of MPs is successfully performed to improve the pigment yields. Mycelial morphology is varied to enhanced pigment secretion, and gene expression is dynamically regulated to promote pigment accumulation in HSSF.

Histone deacetylase MrHos3 negatively regulates the production of citrinin and pigments in Monascus ruber

Monascus spp. can produce a variety of beneficial metabolites widely used in food and pharmaceutical industries. However, some Monascus species contain the complete gene cluster responsible for citrinin biosynthesis, which raises our concerns about the safety of their fermented products. In this study, the gene Mrhos3, encoding histone deacetylase (HDAC), was deleted to evaluate its effects on the production of mycotoxin (citrinin) and the edible pigments as well as the developmental process of Monascus ruber M7. The results showed that absence of Mrhos3 caused an enhancement of citrinin content by 105.1%, 82.4%, 111.9%, and 95.7% at the 5th, 7th, 9th, and 11th day, respectively. Furthermore, deletion of Mrhos3 increased the relative expression of citrinin biosynthetic pathway genes including pksCT, mrl1, mrl2, mrl4, mrl6, and mrl7. In addition, deletion of Mrhos3 led to an increase in total pigment content and six classic pigment components. Western blot results revealed that deletion of Mrhos3 could significantly elevate the acetylation level of H3K9, H4K12, H3K18, and total protein. This study provides an important insight into the effects of hos3 gene on the secondary metabolites production in filamentous fungi.

Optimization of L-glutaminase production by Monascus ruber URM 8542 isolated from ice cream industrial effluent

L-glutaminase is a hydrolytic enzyme with wide biotechnological applications. Mostly, these enzymes are employed in the feed industry for flavor enhancement and acrylamide mitigation. Also, L-glutaminase may have antiviral and antineoplastic effects making it a good choice for pharmaceutical applications. In this study, the strain Monascus ruber URM 8542 was identified through classical and molecular taxonomy using partial sequencing of β-tubulin and calmodulin genes. Subsequently, the optimal culture conditions were evaluated by submerged fermentation (L-glutamine 10 g.L- 1) for L-glutaminase excretion. The isolate was identified as M. ruber URM 8542 which showed significant extracellular enzyme production with a yield of 11.4 times in relation to the specific activity of intracellular L-glutaminase. Regarding the optimization experiments, several factors such as L-glutamine concentration, temperature, and pH were compared using a full factorial design (23). The concentrations greater than 1% proved to be significantly better for glutaminase production (R2 = 0.9077). Additionally, the L-glutaminase was optimally active at pH 7.0 and 30 ºC. The L-glutaminase was remarkably stable across an alkaline pH range (7.0-8.0) and had a thermal stability ranging from 30 ºC to 60 ºC for 1 h. Taken together, these findings suggest that the L-glutaminase produced by M. ruber is a promising candidate for pharmacological application, although further studies need to be performed. To the best of our knowledge, this is the first report of L-glutaminase production by Monascus ruber.

An oxidoreductase gene CtnD involved in citrinin biosynthesis in Monascus purpureus verified by CRISPR/Cas9 gene editing and overexpression

Monascus produces a kind of mycotoxin, citrinin, whose synthetic pathway is still not entirely clear. The function of CtnD, a putative oxidoreductase located upstream of pksCT in the citrinin gene cluster, has not been reported. In this study, the CtnD overexpressed strain and the Cas9 constitutively expressed chassis strain were obtained by genetic transformation mediated by Agrobacterium tumefaciens. The pyrG and CtnD double gene-edited strains were then obtained by transforming the protoplasts of the Cas9 chassis strain with in vitro sgRNAs. The results showed that overexpression of CtnD resulted in significant increases in citrinin content of more than 31.7% and 67.7% in the mycelium and fermented broth, respectively. The edited CtnD caused citrinin levels to be reduced by more than 91% in the mycelium and 98% in the fermented broth, respectively. It was shown that CtnD is a key enzyme involved in citrinin biosynthesis. RNA-Seq and RT-qPCR showed that the overexpression of CtnD had no significant effect on the expression of CtnA, CtnB, CtnE, and CtnF but led to distinct changes in the expression of acyl-CoA thioesterase and two MFS transporters, which may play an unknown role in citrinin metabolism. This study is the first to report the important function of CtnD in M. purpureus through a combination of CRISPR/Cas9 editing and overexpression.

-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.

Coconut Cream Agar as a simple and rapid semiquantitative method to screen citrinin-producing Monascus spp. isolates isolated from red fermented rice

Red fermented rice (RFR) is produced using Monascus spp. This product has some health benefits. However, RFR can also contain the mycotoxin, citrinin (CIT) and that has adverse effects on human health. The objective of the study was to develop a simple and rapid screening method for the detection of Monascus spp. isolates that can produce CIT by using Coconut Cream Agar (CCA). RFR was spread onto CCA and other media and incubated at 30 °C for 7 days. All the media were observed daily under ultraviolet (UV) light and any Monascus spp. colony that produced light blue fluorescence was recorded as a CIT-producer. Two different isolates (MF1 and MS1) isolated from CCA were selected for further analysis. All (100%; 10/10 plates) of CCA inoculated with MF1 produced light blue fluorescence after incubation for 4 days, meanwhile 30% (3/10 plates) of MS1 produced weak fluorescence on CCA after incubation for 7 days. Isolates MF1 and MS1 were identified as M. purpureus with the ability to produce CIT by having polyketide synthase (pksCT) and transcriptional regulator (ctnA) genes. CIT was quantified by high-performance liquid chromatography (HPLC). CCA is a simple and rapid method to detect CIT-producers of Monascus spp.

Utilization of low-cost agricultural by-product rice husk for Monascus pigments production via submerged batch-fermentation

BACKGROUND

Monascus pigments (MPs) produced by the genus Monascus, have been utilized for more than 2000 years in the food industry. In the present study, by submerged batch-fermentation (SBF), we were able to obtain a mutant strain with a high tolerance of inhibitory compounds generated from rice husk hydrolysate, allowing the production of MPs.

RESULTS

The mutant strain, M. Purpureus M523 with high rice husk hydrolysate tolerance was obtained using the atmospheric and room temperature plasma (ARTP) screening system, producing 39.48 U mL^-1 extracellular total MPs (yellow and orange MPs), using non-detoxified rice husk diluted sulfuric acid hydrolysate (RHSAH) as the carbon source in SBF. Extracellular MPs (exMPs) production was enhanced to 72.1 and 80.7 U mL^-1 in supplemented SBF (SSBF) and immobilized fermentation (IF) using non-detoxified RHSAH, with productivities of 0.16 and 0.37 U mL^-1  h^-1 , respectively. In addition, our findings revealed that despite having a high RHSAH tolerance, the mutant strain was unable to degrade phenolic compounds. Furthermore, we discovered that inhibitory compounds, including furfural (Fur) and 5'-hydroxymethyl furfural (5'-HMF), not only inhibit MP biosynthesis, but also regulate the conversion of pigment components.

CONCLUSION

The low-cost agricultural by-product, rice husk, can serve as an efficient substitute for MP production with high productivity via IF by Monascus spp. © 2021 Society of Chemical Industry.

Systematic Metabolic Engineering for the Production of Azaphilones in Monascus purpureus HJ11

Fungal azaphilones have attracted considerable interest as they exhibit great potential in food and pharmacological industries. However, there is a severe bottleneck in the low production in wild strains and the ability to genetically engineer azaphilone-producing fungi. Using Monascus azaphilones (MAs) as an example, we demonstrate a systematic metabolic engineering strategy for improving the production of MAs. In this study, Monascus purpureus HJ11 was systematically engineered through a combination of promoter engineering, gene knockout, rate-limiting enzyme overexpression, repression of the competing pathway, enzyme engineering, and metabolic rebalance. The maximum yield and titer of MAs successfully increased to 906 mg/g dry cell weight (DCW) and 14.6 g/L, respectively, 2.6 and 3.7 times higher than those reported in the literature. Our successful model not only offers a practical and efficient way to improve the azaphilone production but also sheds light on the potential of systematic metabolic engineering in nonmodel fungi as a chassis for the production of high-value chemicals.

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.

Screening and evaluation of Monascus purpureus FJMR24 for enhancing the raw material utilization rate in rice wine brewing

BACKGROUND

The rapid development of the rice wine industry has increased the demand for raw materials worldwide. A fungal strain with good adaptability to rice wine brewing conditions, which can also enhance the utilization rate of raw materials (URRM), thus increasing the production efficiency, was sought in the present research.

RESULTS

The strain FJMR24 was successfully isolated and screened from 35 fermentation starters and exhibited high amylase activity (2200.9 ± 18.5 U g^-1 ) and high glucoamylase activity (2330.4 ± 31.9 U g^-1 ). Based on a morphological examination and a sequence analysis of the internal transcribed spacer (ITS) gene and β-tubulin gene, FJMR24 was identified as Monascus purpureus, which is an edible and versatile fungus that plays a dominant role in the processing of Hong Qu. A moderate pH of 5-6 under incubation at 35 °C for 5-6 days was favorable for the growth and enzyme production of FJMR24. The strain could also tolerate the extreme conditions of 15-45 °C, 18% ethanol (v/v), and an acidity of pH 2. The excellent fermentation adaptability of FJMR24 might enable it to retain high enzyme activity during rice wine brewing. As a result of the action of FJMR24, the URRM of the base liquor increased by around 26% due to increased starch hydrolysis efficiency, which was mainly due to the high unit enzyme activity of FJMR24.

CONCLUSION

This study provides perspectives for the application of a M. purpureus strain with high starch hydrolysis activity for enhancing the URRM in traditional rice wine brewing. © 2020 Society of Chemical Industry.

Divergence of metabolites in three phylogenetically close Monascus species (M. pilosus, M. ruber, and M. purpureus) based on secondary metabolite biosynthetic gene clusters

BACKGROUND

Species of the genus Monascus are considered to be economically important and have been widely used in the production of yellow and red food colorants. In particular, three Monascus species, namely, M. pilosus, M. purpureus, and M. ruber, are used for food fermentation in the cuisine of East Asian countries such as China, Japan, and Korea. These species have also been utilized in the production of various kinds of natural pigments. However, there is a paucity of information on the genomes and secondary metabolites of these strains. Here, we report the genomic analysis and secondary metabolites produced by M. pilosus NBRC4520, M. purpureus NBRC4478 and M. ruber NBRC4483, which are NBRC standard strains. We believe that this report will lead to a better understanding of red yeast rice food.

RESULTS

We examined the diversity of secondary metabolite production in three Monascus species (M. pilosus, M. purpureus, and M. ruber) at both the metabolome level by LCMS analysis and at the genome level. Specifically, M. pilosus NBRC4520, M. purpureus NBRC4478 and M. ruber NBRC4483 strains were used in this study. Illumina MiSeq 300 bp paired-end sequencing generated 17 million high-quality short reads in each species, corresponding to 200 times the genome size. We measured the pigments and their related metabolites using LCMS analysis. The colors in the liquid media corresponding to the pigments and their related metabolites produced by the three species were very different from each other. The gene clusters for secondary metabolite biosynthesis of the three Monascus species also diverged, confirming that M. pilosus and M. purpureus are chemotaxonomically different. M. ruber has similar biosynthetic and secondary metabolite gene clusters to M. pilosus. The comparison of secondary metabolites produced also revealed divergence in the three species.

CONCLUSIONS

Our findings are important for improving the utilization of Monascus species in the food industry and industrial field. However, in view of food safety, we need to determine if the toxins produced by some Monascus strains exist in the genome or in the metabolome.

Quantitative Proteomics Analysis by Sequential Window Acquisition of All Theoretical Mass Spectra-Mass Spectrometry Reveals a Cross-Protection Mechanism for Monascus To Tolerate High-Concentration Ammonium Chloride

To achieve the accumulation of targeted secondary metabolites, microorganisms must adopt various protection mechanisms to avoid or reduce damage to cells caused by abiotic stresses, which formed from the changes of physical and chemical culture conditions. The protection mechanism of Monascus sp. to tolerate high-concentration ammonium chloride was analyzed by sequential window acquisition of all theoretical mass spectra-mass spectrometry proteomics in this work, and the results indicated that abiotic stresses caused by high-concentration ammonium chloride inhibited the synthesis of chitin and glycoprotein, leading to a decrease in cell wall integrity and, thus, affecting cell growth. At the same time, it also inhibited the complex enzyme III and IV activities of the mitochondrial cytochrome respiratory chain, leading to an increase in reactive oxygen species (ROS) levels. With the aim to respond to abiotic stresses, the cross-protection mechanism was implemented in Monascus, including self-protection of the Monascus cell by promoting synthesis of trehalose, a molecular chaperone that facilitates protein folding (such as heat-shock protein) and autophagy-related proteins, through not the enzyme protection system (superoxide dismutase, peroxidase, catalase, NADPH oxidase, and alternative oxidase) but the glutathione/glutaredoxin system, to maintain the intracellular redox state and then eliminate or reduce ROS damage to the cell. At the same time, an alternative respiratory pathway related to NADH dehydrogenase was activated to balance the material and energy metabolism.

Disruption of the Ergosterol Biosynthetic Pathway Results in Increased Membrane Permeability, Causing Overproduction and Secretion of Extracellular Monascus Pigments in Submerged Fermentation

Because Monascus pigments (MPs) predominantly accumulate in the cytoplasm during submerged fermentation, many biotechnologies are applied to enhance the production of extracellular MPs (exMPs) to reduce the downstream processing costs. In this study, the genes monascus_7017 and monascus_8018, identified as ERG4 genes, were knocked out to disrupt the ergosterol biosynthetic pathway and enhance the production of exMPs in Monascus purpureus LQ-6. Double-deletion of EGR4 in M. purpureus LQ-6 reduced ergosterol concentration by 57.14% and enhanced exMP production 2.06-fold. In addition, integrated transcriptomic and proteomic analyses were performed to elucidate the transmembrane secretion mechanism of exMPs based on the relationship between ergosterol synthesis and membrane permeability, which revealed that several metabolic pathways were noticeably dynamic, including fatty acid degradation, amino acid metabolism, energy metabolism, carbohydrate metabolism, and transport. These findings therefore clarified the secretion mechanism of exMPs and provide a novel strategy for further enhancement of exMP production in submerged fermentation.

Polyaromatic Resin HP-20 Induced Accumulation of Intermediate Azaphilones in Monascus purpureus ∆mppC and ∆mpp7 Strains

Monascus purpureus recombinant mppC and mpp7 knockout strains were subjected to extractive fermentation in the context of azaphilone pigment production. Inclusion of Diaion HP-20 resin resulted in the selective production of unreduced azaphilone congeners, in addition to the early intermediate FK17-P2a, from ∆mppC and ∆mpp7 strains that would otherwise mainly produce reduced congeners. Structural determination of two novel unreduced azaphilones from the ∆mpp7 strain was accomplished. The unreduced azaphilone compound was converted into the cognate reduced congener in recombinant M. purpureus strains, demonstrating its intermediate role in azaphilone biosynthesis. This study demonstrates the possibility that extractive fermentation with Diaion HP-20 resin can be used to obtain cryptic azaphilone metabolites.

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.

MptriA, an Acetyltransferase Gene Involved in Pigment Biosynthesis in M. purpureus YY-1

Monascus pigments (Mps) have been used as food colorants for several centuries in Asian countries. MptriA is a putative acetyltransferase gene involved in the MPs biosynthesis. To analyze the function of MptriA, an MptriA disruption strain (Δ MptriA) and a complementation strain (Δ MptriA:: MptriA) were successfully obtained In addition to the loss of color, the disruption of MptriA had little effect on the phenotypes during growth on four different media. The Δ MptriA strain showed decreased pigment and citrinin production during the liquid-fermentation process. Transcriptional analysis showed that the expression of several genes involved in the synthesis of pigments and citrinin was down-regulated in Δ MptriA. These results demonstrated that the role of MptriA was to transfer an acyl group to the pyranoquinone structure of the polyketide chromophore during Monascus pigment biosynthesis and to influence the citrinin biosynthesis pathway. This study contributes to the exploration of pigment biosynthesis in M. purpureus.

Determination of two potential toxicity metabolites derived from the disruption of the pksCT gene in Monascus aurantiacus Li As3.4384

BACKGROUND

We previously demonstrated that disruption of the pksCT gene of Monascus led to a greater than 98% decrease in its citrinin production capacity in Monascus (PHDS26). Two potentially toxic compounds, monascopyridine A (MPA) and monascopyridine B (MPB), were found in the fermentation products of the pksCT gene-disrupted Monascus. Moreover, a rapid and reliable high-performance liquid chromatography method was developed for the simultaneous determination of MPA and MPB. We studied the effects of various extraction parameters and designed an orthogonal experiment to investigate the importance of each factor.

RESULTS

The optimal extraction conditions were: methanol concentration, 90%; extraction temperature, 40 °C; extraction time, 10 min; two extraction cycles; and a solid-liquid ratio of 1:25. Under the optimal chromatographic conditions, good linearity was reached over the concentration ranges 0.5-200 µg mL^-1 and 0.5-300 µg mL^-1 for MPA and MPB, respectively, and the corresponding determination coefficients were 0.9999 and 0.9997. The percentage relative standard deviation values of within-day and between-day precision for MPA were 2.0% and 2.1%, respectively; the corresponding values for MPB were 4.8% and 4.6%. The average recovery for MPA and MPB was 99.9% and 94%, respectively.

CONCLUSION

Maximum MPA and MPB yields (2073.7 and 1961.7 µg g^-1 , respectively) were observed after 16 days of cultivation. © 2017 Society of Chemical Industry.

Comparative analysis of genetic polymorphisms among Monascus strains by ISSR and RAPD markers

BACKGROUND

The genus Monascus includes several species of fungi valued across Asia for their culinary uses and diverse medicinal properties. In this study, we evaluated the applicability of random amplified polymorphic DNA (RAPD) and inter-simple sequence repeats (ISSR) markers in characterizing the genetic diversity in 41 Monascus strains collected from various regions of Fujian Province, the leading producer of Monascus in China.

RESULTS

Seven screened ISSR primers generated 56 polymorphic bands, of which 93.33% were polymorphic. The genetic similarity coefficients (GSC) of the strains ranged from 0.50 to 1.00. Comparative sequence analysis using seven screened RAPD primers amplified a total of 49 polymorphic bands, of which 81.67% were polymorphic; GSC values ranged from 0.62 to 1.00.

CONCLUSION

Correlation analysis revealed a significant positive correlation in genetic distances assessed using above two markers, which indicated they were suitable for Monascus species characterization. ISSR markers were more suitable for the classification and determination of Monascus species, while RAPD markers appear to be preferable for analyzing the differences among strains within the same species. Our study revealed that Monascus possesses rich genetic diversity, and that the genetic relationships among the selected strains were, to a very limited extent, correlated to their geographical variation. © 2016 Society of Chemical Industry.

Effects of Light Intensity and Color on the Biomass, Extracellular Red Pigment, and Citrinin Production of Monascus ruber

Light is a crucial environmental signal for fungi. In this work, the effects of different light intensities and colors on biomass, Monascus pigments (MPs) and citrinin production of Monascus ruber M7 were investigated. We have demonstrated that low intensity of blue light (500 lx) decreased Monascus biomass, increased MPs accumulation via upregulation of MpigA, MpigB, and MpigJ genes expression, but had no significant influence on citrinin production. High intensity of blue light (1500 lx) decreased citrinin accumulation but had no significant influence on biomass and MPs production after 14 days cultivation. Low intensity of green light (500 lx) stimulated citrinin production via upregulation of pksCT, mrl1, mrl2, and ctnA genes expression. One putative red light photoreceptor and two putative green light photoreceptors were identified in M. ruber M7. These observations will not only guide the practical production of Monascus but also contribute to our understanding light effects on Monascus.

Metabolic Effects of the pksCT Gene on Monascus aurantiacus Li As3.4384 Using Gas Chromatography--Time-of-Flight Mass Spectrometry-Based Metabolomics

Monascus spp. have been used for the production of natural pigments and bioactive compounds in China for several centuries. Monascus can also produce the mycotoxin citrinin, restricting its use. Disruption of the pksCT gene in Monascus aurantiacus Li AS3.4384 reduces citrinin production capacity of this strain (Monascus PHDS26) by over 98%. However, it is unclear how other metabolites of M. aurantiacus Li AS3.4384 (the wild-type strain) are affected by the pksCT gene. Here, we used metabolomic analyses to compare red yeast rice (RYR) metabolite profiles of the wild-type strain and Monascus PHDS26 at different stages of solid-state fermentation. A total of 18 metabolites forming components within the glycolysis, acetyl-CoA, amino acid, and tricarboxylic acid (TCA) cycle metabolic processes were found to be altered between the wild-type strain and Monascus PHDS26 at different stages of solid-state fermentation. Thus, these findings provide important insights into the metabolic pathways affected by the pksCT gene in M. aurantiacus.

Enhancement of yellow pigment production by intraspecific protoplast fusion of Monascus spp. yellow mutant (ade(-)) and white mutant (prototroph)

To breed industrially useful strains of a slow-growing, yellow pigment producing strain of Monascus sp., protoplasts of Monascus purpureus yellow mutant (ade(-)) and rapid-growing M. purpureus white mutant (prototroph) were fused and fusants were selected on minimal medium (MM). Preliminary conventional protoplast fusion of the two strains was performed and the result showed that only white colonies were detected on MM. It was not able to differentiate the fusants from the white parental prototroph. To solve this problem, the white parental prototroph was thus pretreated with 20mM iodoacetamide (IOA) for cytoplasm inactivation and subsequently taken into protoplast fusion with slow-growing Monascus yellow mutant. Under this development technique, only the fusants, with viable cytoplasm from Monascus yellow mutant (ade(-)), could thus grow on MM, whereas neither IOA pretreated white parental prototroph nor yellow auxotroph (ade(-)) could survive. Fifty-three fusants isolated from yellow colonies obtained through this developed technique were subsequently inoculated on complete medium (MY agar). Fifteen distinguished yellow colonies from their parental yellow mutant were then selected for biochemical, morphological and fermentative properties in cassava starch and soybean flour (SS) broth. Finally, three most stable fusants (F7, F10 and F43) were then selected and compared in rice solid culture. Enhancement of yellow pigment production over the parental yellow auxotroph was found in F7 and F10, while enhanced glucoamylase activity was found in F43. The formation of fusants was further confirmed by monacolin K content, which was intermediate between the two parents (monacolin K-producing yellow auxotroph and non-monacolin K producing white prototroph).

PP-O and PP-V, Monascus pigment homologues, production, and phylogenetic analysis in Penicillium purpurogenum

The production of pigments as secondary metabolites by microbes is known to vary by species and by physiological conditions within a single strain. The fungus strain Penicillium purpurogenum IAM15392 has been found to produce violet pigment (PP-V) and orange pigment (PP-O),Monascus azaphilone pigment homologues, when grown under specific culture conditions. In this study, we analysed PP-V and PP-O production capability in seven strains of P. purpurogenum in addition to strain IAM15392 under specific culture conditions. The pigment production pattern of five strains cultivated in PP-V production medium was similar to that of strain IAM15392, and all violet pigments produced by these five strains were confirmed to be PP-V. Strains that did not produce pigment were also identified. In addition, two strains cultivated in PP-O production medium produced a violet pigment identified as PP-V. The ribosomal DNA (rDNA) internal transcribed spacer (ITS) region sequences from the eight P. purpurogenum strains were sequenced and used to construct a neighbor-joining phylogenetic tree. PP-O and PP-V production of P. purpurogenum was shown to be related to phylogenetic placement based on rDNA ITS sequence. Based on these results, two hypotheses for the alteration of pigment production of P. purpurogenum in evolution were proposed.

[Identification of a pigment-polyketide synthase gene deleted mutant of Monascus ruber M7]

OBJECTIVE

To reveal the function of a polyketide synthase gene (pksPT), probably responsible for the synthesis of Monascus pigments in Monascus ruber M7.

METHODS

The pksPT was analyzed using bioinformatics method; it was disrupted using Agrobacterium tumefaciens mediated transformation method, generating the pksPT-deleted mutant (ΔpksPT). Colonial morphology, conidial germination, pigment and citrinin production, and growth rate of ΔpksPT were analyzed.

RESULTS

The pksPT with the length of 8687 bp encoded a putative protein of 2690 amino acids, which is a non-reduced type III polyketide synthase and has some active domains with the arrangement of KS (β-ketosynthase)-AT (Acyltransferase)-ACP (Acyl carrier protein)-ACP-ME (Methyltransferase). The analysis of ΔpksPT displayed that it could generate cleistothecum and conidum normally and was unable to produce any kinds of Monascus pigments; compared to M7, the growth rate of ΔpksPT was increased obviously and the yield of citrinin in ΔpksPT was increased about 2. 8 times.

CONCLUSION

pksPT is of extremely importance to the biosynthetic pathways of Monascus pigments in M7 and the synthesis of Monascus pigments gives a significant effect on the produce of citrinin as well as the growth of M7.

Effects of the Principal Nutrients on Lovastatin Production byMonascus pilosus

Lovastatin production is dependent on the substrates provided. We investigated how several carbon and nitrogen sources in the medium affect lovastatin production by Monascus pilosus. M. pilosus required a suitable concentration of organic nitrogen peptone for high lovastatin production. As sole carbon source with peptone, although glucose strongly repressed lovastatin production, maltose was responsible for high production. Interestingly, glycerol combined with maltose enhanced lovastatin production, up to 444 mg/l in the most effective case. Moreover, an isolated mutant, in which glucose repression might be relieved, easily produced the highest level of lovastatin, 725 mg/l on glucose-glycerol-peptone medium. These observations indicate that lovastatin production by M. pilosus is regulated by strict glucose repression and that an appropriate release from this repression by optimizing medium composition and/or by a mutation(s) is required for high lovastatin production.

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.

Lower citrinin production by gene disruption of ctnB involved in citrinin biosynthesis in Monascus aurantiacus Li AS3.4384

The filamentous fungi Monascus spp. have been used in the production of food colorants and health remedies for more than 1000 years in Asia. However, greater attention has been given to the safety of Monascus products because they contain citrinin, which is harmful to the hepatic and renal systems. The citrinin biosynthetic gene cluster has been characterized in Monasucs aurantiacus . The ctnB gene encoding an oxidoreductase is located between pksCT and ctnA. In this study, a ctnB replacement vector (pCTNB-HPH) was constructed to disrupt the ctnB gene with a hygromycin resistance gene as the selection marker. The linear vector was transformed into M. aurantiacus using the protoplast CaCl2/polyethylene glycol (PEG) method. Three ctnB-disrupted strains were obtained by homologous recombination. In comparison to the parental strain, the ΔctnB mutants barely produced citrinin. These data confirmed that the ctnB gene is directly involved in citrinin biosynthesis. Moreover, the yields of the pigments of two disruptants were similar to that of the wild-type strain, but the yield of another mutant was slightly higher than that of the latter strain. These results indicate that the production of the mycotoxin citrinin was successfully eliminated through genetic engineering.

Elevated yield of monacolin K in Monascus purpureus by fungal elicitor and mutagenesis of UV and LiCl

In China, Monascus spp., a traditional fungus used in fermentation, is used as a natural food additive. Monascus spp. can produce a secondary metabolite, monacolin K namely, which is proven to be a cholesterol-lowering and hypotensive agent. Hence, recently, many researchers have begun focusing on how to increase the production of monacolin K by Monascus purpureus. In the present study, we investigated the effect of the fungal elicitor and the mutagenesis of UV & LiCl on the amount of monacolin K produced by Monascus purpureus. The fugal elicitor, Sporobolomyces huaxiensis, was isolated from tea leaves and its filtrate was added into the culture filtrate of Monascus purpureus during growth to induct the production of monacolin K. The results showed that the highest amount of monacolin K produced by the liquid fermentation was 446.92 mg/mL, which was produced after the fungal elicitor was added to the culture filtrate of Monascus purpureus on the day 4; this amount was approximately 6 times greater than that of the control culture filtrate, whereas the highest amount of monacolin K produced by the mutated strain was 3 times greater than the control culture after the irradiation of UV light in the presence of 1.0 % LiCl in the medium.

Isolation and characterization of the citrinin biosynthetic gene cluster from Monascus aurantiacus

Monascus aurantiacus produces high amounts of citrinin which is a mycotoxin with nephrotoxic activity. Six putative citrinin biosynthesis genes have been discovered in M. purpureus and at least 10 genes are responsible for its biosynthesis. However, the sequence of citrinin pathway gene cluster in M. aurantiacus has not been reported. Here, the putative sequence of citrinin biosynthetic gene cluster was obtained by a PCR-based strategy for screening a genome fosmid library of M. aurantiacus. A sequence of 43 kb revealed 16 ORFs including the six putative biosynthetic genes reported previous. The putative gene cluster consists of a polytekide synthetase encoding one PKS module, an oxidoreductase gene, three dehydrogenase genes, an acyl-coenzyme A synthetase gene, a membrane transport protein gene, a transcriptional activator gene as well as genes encoding proteins of undefined function.

Identification of the mokH gene encoding transcription factor for the upregulation of monacolin K biosynthesis in Monascus pilosus

Monacolin K is a secondary metabolite synthesized by polyketide synthases (PKS) from Monascus. The monacolin K biosynthetic gene cluster, mokA-mokI, has been characterized in Monascus pilosus. The mokH gene encoding Zn(II)2Cys6 binuclear DNA binding protein is assumed to be an activator for monacolin K production. In this study, the mokH gene was cloned and driven by the glyceraldehyde-3-phosphate dehydrogenase (gpd) promoter for overexpression in M. pilosus. The transformants containing an extra copy of the mokH gene were obtained and verified by PCR and Southern hybridization. The transcripts of mokH in the transformants were expressed significantly higher than those of the wild-type strain. The transformants were stably inherited through the next generation, as determined by observation of the enhanced green fluorescent protein (EGFP). The transformant T-mokH1 also showed a 1.7-fold higher production of monacolin K than the wild-type strain in a time course analysis. Analysis of the RT-PCR products demonstrated that the monacolin K biosynthetic genes in the transformant were expressed to a greater extent than those in the wild-type strain. These results indicated that mokH upregulated the transcription of monacolin K biosynthetic genes and increased monacolin K production.

Construction of a Monascus purpureus mutant showing lower citrinin and higher pigment production by replacement of ctnA with pks1 without using vector and resistance gene

Monascus products are used as both natural colorants and food additives all over the world. However, its safety is really an issue because of the presence of citrinin, which is considered to be hepatotoxic and nephrotoxic. Therefore, the objective of the present study was to develop an approach for using a fragment of pigment-related gene pks1 to replace citrinin-activator gene ctnA. The character of citrinin antibacterial activity to Bacillus subtilis was used for primary screening of transformants based on the foundation that the inhibition zone formed around the mutant colonies with low citrinin products will become smaller. The selected mutants were then further confirmed by polymerase chain reaction and high-performance liquid chromatography methods. During all of the processes, antibiotic markers and vectors were avoided. The results showed that the citrinin products of mutants were reduced to 42%, while the pigment products were improved to 33.9%, respectively, over those of the wild-type strains.

[Construct cosmid libraries by isolating large genomic DNA fragments from Monascus ruber]

OBJECTIVE

To isolate large genomic DNA fragments from Monascus ruber for the construction of cosmid libraries.

METHODS

Modified phenol-chloroform method was used to isolate genomic DNA. The isolated genomic DNA was digested by Sau3AI to 40kb fragments on average. Then, the fragments were packaged by Stratagene' s Gigapack III XL packaging extract. A pair of degenerate primers were used to amplify a fragment of PKS (polyketide synthase) gene from this cosmid library.

RESULTS

The average size of genomic DNA isolated by this method was larger than 48 kb, with a concentration of 5 microg/microl. The constructed cosmid libraries had 10 folders coverage of the Monascus spp. genome. A cosmid containing the homologue of PKS gene was obtained by PCR screening.

CONCLUSION

This modified method of isolating large fragments genomic DNA of Monascus ruber was efficient and feasible.

Development and media regulate alternative splicing of a methyltransferase pre-mRNA in Monascus pilosus

Two alternatively spliced mRNAs (d- and l-MpLaeA) of a methyltransferase gene (MpLaeA) were identified from Monascus pilosus IFO4520 and its mutant MK-1. Alternative splicing of the MpLaeA pre-mRNA occurred in the 5'-untranslated region (5'-UTR). The alternative splicing patterns of MpLaeA were regulated by the fungal growth stage and the principal nutrients: that is, the short l-MpLaeA mRNA was a constitutive transcript at all growth stages and different carbon or nitrogen sources, but the glutamate and NaNO(3) as main nitrogen source could up-regulate the long d-MpLaeA mRNA form. The long spliced 5'-UTR of d-MpLaeA blocked GFP expression in Escherichia coli , suggesting that d-MpLaeA mRNA was an ineffective spliced mRNA. Down-regulation of MpLaeA by transgenic antisense d-MpLaeA cDNA resulted in decreasing synthesis of monacolin K in M. pilosus. This suggested that the alternative splicing of MpLaeA mRNA might regulate the synthesis of monacolin K.

Exploring the distribution of citrinin biosynthesis related genes among Monascus species

Citrinin, a hepato-nephrotoxic compound to humans, can be produced by the food fermentation microorganisms Monascus spp. In this study, we investigated the distribution of mycotoxin citrinin biosynthesis genes in 18 Monascus strains. The results show that the acyl-transferase and keto-synthase domains of the pksCT gene encoding citrinin polyketide synthase were found in Monascus purpureus, Monascus kaoliang, and Monascus sanguineus. Furthermore, the ctnA gene, a major activator for citrinin biosynthesis, was found in M. purpureus and M. kaoliang, but was absent in M. sanguineus. The orf3 gene encoding oxygenase, located between pksCT and ctnA, was also present in M. purpureus and M. kaoliang. The pksCT gene was highly conserved in M. purpureus, M. kaoliang, and M. sanguineus, while the ctnA and orf3 genes were shown to be highly homologous in M. purpureus and M. kaoliang. In contrast, the PCR and Southern blot analyses suggest that pksCT, ctnA, and orf3 were absent or significantly different in Monascus pilosus, Monascus ruber, Monascus barkeri, Monascus floridanus, Monascus lunisporas, and Monascus pallens. A citrinin-producing phenotype was detected only in M. purpureus and M. kaoliang using high performance liquid chromatography (HPLC). These results clearly indicate that the highly conserved citrinin gene cluster in M. purpureus and M. kaoliang carry out citrinin biosynthesis. In addition, according to the phylogenetic subgroups established with the beta-tubulin gene, the citrinin gene cluster can group the species of Monascus.

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

Monacolin K is a secondary metabolite synthesized by polyketide synthases (PKS) from Monascus, and it has the same structure as lovastatin, which is mainly produced by Aspergillus terreus. In the present study, a bacterial artificial chromosome (BAC) clone, mps01, was screened from the BAC library constructed from Monascus pilosus BCRC38072 genomic DNA. The putative monacolin K biosynthetic gene cluster was found within a 42 kb region in the mps01 clone. The deduced amino acid sequences encoded by the nine genes designated as mokA- mokI, which share over 54% similarity with the lovastatin biosynthetic gene cluster in A. terreus, were assumed to be involved in monacolin K biosynthesis. A gene disruption construct designed to replace the central part of mokA, a polyketide synthase gene, in wild-type M. pilosus BCRC38072 with a hygromycin B resistance gene through homologous recombination, resulted in a mokA-disrupted strain. The disruptant did not produce monacolin K, indicating that mokA encoded the PKS responsible for monacolin K biosynthesis in M. pilosus BCRC38072.

Agrobactrium tumefaciens-mediated transformation of Monascus ruber

Agrobacterium tumefaciens-mediated transformation (ATMT) was successfully applied to Monascus ruber. The optimum cocultivation time was 84 h with an efficiency of 900 to 1,000 transformants when 1x106 spores were used with the same volume of bacteria. The stability of transformants was over 98% after five generations. When M. ruber was transformed with A. tumefaciens YL-63 containing the green fluorescent protein gene (egfp), the green fluorescent signal was observed throughout hyphae, confirming expression of the gene. This efficient transformation and expression system of M. ruber by ATMT will facilitate the study of this fungus at a molecular genetic level.

[Application of SCAR molecular marker technology in identification of Monascus strains]

OBJECTIVE

To establish an effective way for rapid identification of Monascus strains based on DNA molecular marker.

METHOD

A random amplified polymorphic DNA (RAPD) marker named F421 in genomic DNA of Monascus F strain was observed during a comparison of DNA fingerprints derived from 10 cultivated strains of Monascus. F421 was cloned and sequenced. Comparing the sequence of F421 (GenBank accession number EF063107) with other relative sequences in the GenBank databases, no distinct comparability was found. A pair of sequence characterized amplified region (SCAR) primers were designed based on the sequence of the cloned fragment and tested for the specific detection of Monascus F.

RESULT

The results of polymerase chain reaction showed that only a 421bp segment of Monascus F strain was amplified compared with other 9 cultivated strains of Monascus. And the acquired SCAR marker of strain F could be used as a specific DNA fingerprint to identify Monascus strain F within one day.

CONCLUSION

SCAR molecular marker technology is an effective new way to identify Monascus strains more rapidly. And also is an assistant tool to identify Monascus strains more accurately when disagreements come out using traditional classification. It could be applied widely to the protection of germ plasm resources, classification and identification distinguishing false strains of pharmaceutical fungi.

Optimization of production of monacolin K from gamma-irradiated Monascus mutant by use of response surface methodology

Monascus isolate number 711, which is capable of producing monacolin K as an inhibitor of 3-hydroxy-3-methylglutaryl-coenzyme A reductase, the key enzyme of cholesterol synthesis, was isolated from Ang-kak, the red yeast rice koji. To increase the monacolin K-producing activity of the strain, spore suspensions of the strain were subjected to gamma-irradiation. One thousand mutants were generated via gamma-irradiation and screened using bioassay and high performance liquid chromatography analysis. Several mutants with higher productivities of monacolin K than that of the parent strain were primarily selected. Mutant KU609 was finally selected because of its characteristics of high monacolin K production and non-citrinin-producing activity under our test conditions. Response surface methodology was used to analyze the effect of culture medium on the production of monacolin K in mixed solid-state cultures. The optimal values of nutritional ingredients for the maximal production were soytone, glucose, MgSO4, and barley at concentrations of 0.5 g, 0.48 g, 0.053 g, and 9 g, respectively. The final monacolin K production of Monascus KU609 was increased almost 100-fold compared to that of the parent strain.

Identification and in vivo functional analysis by gene disruption of ctnA, an activator gene involved in citrinin biosynthesis in Monascus purpureus

Citrinin, a secondary fungal metabolite of polyketide origin, is moderately nephrotoxic to vertebrates, including humans. From the red-pigment producer Monascus purpureus, a 21-kbp region flanking pksCT, which encodes citrinin polyketide synthase, was cloned. Four open reading frames (ORFs) (orf1, orf2, orf3, and orf4) in the 5'-flanking region and one ORF (orf5) in the 3'-flanking region were identified in the vicinity of pksCT. orf1 to orf5 encode a homolog of a dehydrogenase (similarity, 46%), a regulator (similarity, 38%), an oxygenase (similarity, 41%), an oxidoreductase (similarity, 26%), and a transporter (similarity, 58%), respectively. orf2 (2,006 bp with four introns) encodes a 576-amino-acid protein containing a typical Zn(II)2Cys6 DNA binding motif at the N terminus and was designated ctnA. Although reverse transcriptase PCR analysis revealed that all of these ORFs, except for orf1, were transcribed with pksCT under citrinin production conditions, the disruption of ctnA caused large decreases in the transcription of pksCT and orf5, together with reduction of citrinin production to barely detectable levels, suggesting that these two genes are under control of the ctnA product. Complementation of the ctnA disruptant with intact ctnA on an autonomously replicating plasmid restored both transcription and citrinin production, indicating that CtnA is a major activator of citrinin biosynthesis.

Identification of a cerulenin resistance gene from Monascus pilosus

Detoxification is essential for the fungal growth in the drug stress environments, and the multidrug transporters play an important role in this process. Here a cerulenin transporter gene (MpMdt, AB206476) was identified from Monascus pilosus. MpMdt mRNA contains 1951 bp and encodes a protein of 559 amino acid residues with 11 trans-membrane domains; and there is no difference in the sequence of MpMdt mRNA between the wild type M. pilosus IFO4520 and its cerulenin resistant mutant MK-1. Up-expression of MpMdt renders the cerulenin resistance of the mutant MK-1. Over-expression of MpMdt could also increase the cerulenin tolerance in the transgenic M. pilosus IFO4520. These results suggested that MpMdt is able to efflux-transport the anti-fungal antibiotic cerulenin and increase the cerulenin resistance of M. pilosus.

Cloning and sequence analysis of the full-length cDNA of a novel yp05 gene associated with citrinin production in Monascus aurantiacus

OBJECTIVE

To obtain the full-length cDNA of a novel gene (named yp05) associated with citrinin production-related genes in Monascus aurantiacus.

METHODS

Total RNA was extracted from mycelium, 3' and 5' cDNA end of yp05 gene was amplified using smart trace cDNA amplification kit, and the full-length cDNA of a novel gene (named yp05) was obtained from the electronic assembly of 3'-RACE and 5'-RACE products.

RESULTS

This yp05 gene was 787 bp including a 597 bp open reading frame (ORF) and encoded a deduced protein with 199 amino acid residues, and the amino acid sequence of this protein was found similar with the sequences of many fungal manganese-superoxide dismutases in the GenBank with the aid of BLASTp. The transcription of yp05 gene in Monascus strains was analyzed with the aid of Northern blotting. The transcription of yp05 gene was only detected in Monascus strains, provided that citrinin was produced.

CONCLUSION

The transcription of yp05 gene belongs to differential expression genes of citrinin yielded from Monascus and has no correlation with the biosynthesis pathway of red pigments.

Construction of a replacement vector to disrupt pksCT gene for the mycotoxin citrinin biosynthesis in Monascus aurantiacus and maintain food red pigment production

More and more people pay attention to citrinin produced by Monascus, which has nephrotoxic activity in mammals. It was reported that pksCT gene is responsible for citrinin biosynthesis in Monascus purpureus. In this paper, two DNA fragments in both ends of pksCT were amplified by genomic PCR from fourteen Monascus spp. strains. The PCR products were gained from all of the strains. It is suggested that pksCT gene was highly conserved in different citrinin-producing Monascus strains. A pksCT-replacement vector (pHD106) was constructed to disrupt pksCT with a hygromycin resistance gene as the selection marker, and was transformed into M. aurantiacus Li AS3.4384. Three transformants (M. aurantiacus PHDS18, PHDS26, PHDS31) were selected from transformant selective plates. The targeting fragment D was gained by genomic PCR from PHDS18 and PHDS26 except PHDS31. The expressing citrinin capacities of PHDS26 was decreased by about 98%, while PHDS18 was reserved the high capacity of producing citrinin, after 10 days of growth on YM medium. The results indicated that PHDS26 is a pksCT-disrupted strain. There are maybe other genes besides pksCT responsible for citrinin biosynthesis in M. aurantiacus. It is the effective way to solve the problem of citrinin in M. aurantiacus products by constructing replacement vectors to disrupt the genes responsible for citrinin biosynthesis to reduce the capacity of expressing citrinin.

Characterization of an hyperpigmenting mutant of Monascus purpureus IB1: identification of two novel pigment chemical structures

Monascus purpureus IB1 produces about 50-fold higher levels of azaphilone pigments than M. purpureus NRRL1596. Differently pigmented mutants were obtained from M. purpureus IB1 by nitrosoguanidine treatment. A highly pigmented strain, M. purpureus HP14, was found to lack the formation of the classical yellow and orange azaphilones and was found to produce only about 10% of the red azaphilone pigments. The intense color was associated with novel pigments as shown by high-performance liquid chromatography (HPLC). The addition of hexanoic acid to M. purpureus IB1 resulted in higher volumetric and specific red pigment productivity, but in a complete absence of the classical orange azaphilones, while the classical yellow and red azaphilone pigments were severely reduced; new peaks corresponding to less hydrophobic pigments were found in hexanoic-supplemented cultures by HPLC. Purification of pigments from hexanoic-supplemented cultures showed the presence of five new pigments as indicated by the absorption spectra and HPLC analysis. Two of them, R3 and Y3, were characterized by nuclear magnetic resonance as 9-hexanoyl-3-(2-hydroxypropyl)-6a-methyl-9,9a-dihydro-6H-furo[2,3-h]isochromene-6,8(6aH)-dione and 4-[2,4-dihydroxy-6-(3-hydroxybutanethioyloxy)-3-methylphenyl]-3,4-dihydroxy-3,6-dimethylheptanoic acid. These pigments were also found to be present in cultures of the high-producing mutant M. purpureus HP14. These new pigments are less hydrophobic than the classical azaphilones and may have better properties as natural colorants in the food industry.

[Comparison of different transformation methods for Monascus sp]

In order to facilitate the producer of polyketide pathway, four different transformation methods were tested and compared in an attempt to develop the genetic transformation system of Monascus sp. Using vector pBC-Hygro, the fungus was transformed to be hygromycin B-resistant, by conventional transformation as well as electroporation based on protoplast, electroporation based on germinated conidia, and restriction enzyme-mediated integration (REMI). Electroporation based on germinated conidia was found to be inappropriate for transforming Monascus sp. due to a low transformation frequency. The conventional transformation and electroporation technique based on protoplasts were thought not to be fit for transforming Monascus sp., due to a low stability of transformants though they yielded up to 135 transformants and 125 transformants per microgrammol/Lol/Le DNA, respectively. Transformant number was increased by 20-fold by REMI (2,500 transformants per microgrammol/Lol/Le DNA) and 70%-75% of them were stable. REMI technique would be very beneficial to the establishment of the genetic transformation system of Monascus sp.

Development of Transformation System in Monascus Purpureus using an Autonomous Replication Vector with Aureobasidin A Resistance Gene

To enhance the variety of genetic tools and thus to promote molecular genetic study, aureobasidin A and its resistance gene were adopted as a new marker system together with the incorporation of the Gateway system to facilitate the introduction of long heterologous DNA fragments into Monascus purpureus. The minimum inhibitory concentration of aureobasidin A against Monascus was 0.05 microg/ml and a transformation efficiency of 17 colonies/microg DNA was obtained by the protoplast-PEG method with the vector pAUR316, containing the aureobasidin A resistance gene. Southern analysis of the transformants confirmed that pAUR316 exists as an independent vector, demonstrating that the AMA1 sequence acts as the autonomous replication sequence in M. purpureus. Through the use of the Gateway system, a polyketide synthase gene (7.8 kbp) responsible for citrinin biosynthesis was introduced. As a result, the transformants showed 1.5-fold higher production of citrinin than the wild-type strain.