Enhanced production of natural yellow pigments from Monascus purpureus by liquid culture: The relationship between fermentation conditions and mycelial morphology

Research on pear residue dietary fiber and Monascus pigments extracted through liquid fermentation

Pear residue, a byproduct of pear juice extraction, is rich in soluble sugar, vitamins, minerals, and cellulose. This study utilized Monascus anka in liquid fermentation to extract dietary fiber (DF) from pear residue, and the structural and functional characteristics of the DF were analyzed. Soluble DF (SDF) content was increased from 7.9/100 g to 12.6 g/100 g, with a reduction of average particle size from 532.4 to 383.0 nm by fermenting with M. anka. Scanning electron microscopy and infrared spectroscopic analysis revealed more porous and looser structures in Monascus pear residue DF (MPDF). Water-, oil-holding, and swelling capacities of MPDF were also enhanced. UV-visible spectral analysis showed that the yield of yellow pigment in Monascus pear residue fermentation broth (MPFB) was slightly higher than that in the Monascus blank control fermentation broth. The citrinin content in MPFB and M. anka seed broth was 0.90 and 0.98 ug/mL, respectively. Therefore, liquid fermentation with M. anka improved the structural and functional properties of MPDF, suggesting its potential as a functional ingredient in food.

The effects of environmental factors on the synthesis of water-soluble Monascus red pigments via submerged fermentation: a review

Monascus pigments (MPs) have been used as natural food pigments for many years. There is a high demand for Monascus red pigments (MRPs) to enhance color and for antibacterial and cancer prevention therapies in food and medicine. Most MRPs are not water soluble, and the yield of water-soluble MRPs is naturally low. On the other hand, water-soluble MRP is more cost effective for application in industrial mass production. Therefore, it is important to improve the yield of water-soluble MRPs. Environmental factors have a significant influence on the synthesis of water-soluble MRPs, which is crucial for the development of industrial production of water-soluble MRPs. This review introduces the biosynthetic pathways of water-soluble MRPs and summarizes the effects of environmental factors on the yield of water-soluble MRPs. Acetyl coenzyme A (acetyl-CoA) is a precursor for MPs synthesis. Carbon and nitrogen sources and the carbon/nitrogen ratio can impact MP production by regulating the metabolic pathway of acetyl-CoA. Optimization of fermentation conditions to change the morphology of Monascus can stimulate the synthesis of MPs. The appropriate choice of nitrogen sources and pH values can promote the synthesis of MRPs from MPs. Additives such as metal ions and non-ionic surfactants can affect the fluidity of Monascus cell membrane and promote the transformation of MRPs into water-soluble MRPs. This review will lay the foundation for the industrial production of water-soluble MRPs. © 2024 Society of Chemical Industry.

Insight into advances for the biosynthetic progress of fermented echinocandins of antifungals

Invasive fungal infections have increased remarkably, which have become unprecedented concern to human health. However, the effectiveness of current antifungal drugs is limited due to drug resistance and toxic side-effects. It is urgently required to establish the effective biosynthetic strategy for developing novel and safe antifungal molecules economically. Echinocandins become a promising option as a mainstay family of antifungals, due to specifically targeting the fungal specific cell wall. To date, three kinds of echinocandins for caspofungin, anidulafungin, and micafungin, which derived from pneumocandin B0 , echinocandin B, and FR901379, are commercially available in clinic and have shown potential in managing invasive fungal infections in a cost-effective manner. However, current echinocandins-derived precursors all are produced by environmental fungal isolates with long fermentation cycle and low yields, which challenge the production efficacy of these precursors in industry. Therefore, understanding their biosynthetic machinery is of great importance for improving antifungal titres and creating new echinocandins-derived products. With the development of genome-wide sequencing and establishment of gene-editing technology, there are a growing number of reports on echinocandins-derived products and their biosynthetic gene clusters. This review briefly summarizes the discovery and development history of echinocandins, compares their structural characteristics and biosynthetic processes, and sums up existed strategies for improving their production. Moreover, the genomic analysis of related biosynthetic gene clusters of echinocandins is discussed, highlighting the similarities and differences among the clusters. Last, the biosynthetic processes of echinocandins are compared, focusing on the activation and attachment of side-chains and the formation of the hexapeptide core. This review aims to provide insights into the development and production of new echinocandin drugs by modifying the structure of echinocandin-derived precursors and/or optimizing the fermentation processes; and achieve a new microbial chassis for efficient production of echinocandins in heterologous hosts.

Multiplex metabolic pathway engineering of Monascus pilosus enhances lovastatin production

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

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.

Solid-state fermentation of Saba banana peel for pigment production by Monascus purpureus

Eco-friendly natural pigment demand has ever-increasing popularity due to health and environmental concerns. In this context, the aim of this study was to evaluate the feasibility use of Saba banana peel as low-cost fermentable substrate for the production of pigments, xylanase and cellulase enzymes by Monascus purpureus. Among the strains tested, M. purpureus TISTR 3385 produced pigments better and had higher enzyme activities. Under the optimal pigment-producing conditions at the initial moisture content of 40% and initial pH of 6.0, the pigments comprising yellow, orange, and red produced by the fungi were achieved in the range of 0.40-0.93 UA/g/day. The maximum xylanase and cellulase activities of 8.92 ± 0.46 U/g and 4.72 ± 0.04 U/g were also obtained, respectively. More importantly, solid-state fermentation of non-sterile peel could be achieved without sacrificing the production of the pigments and both enzymes. These indicated the potential use of the peel as fermentable feedstock for pigment production by the fungi and an environmental-friendly approach for sustainable waste management and industrial pigment and enzyme application.

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

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

Enhancement of triterpene production via in situ extractive fermentation of Sanghuangporus vaninii YC-1

There have been many studies on the activities and polysaccharide production of Sanghuangporus vaninii. However, few studies have looked at triterpene production from S. vaninii using liquid-state fermentation. A method for enhancing the production of triterpenes by in situ extractive fermentation (ISEF) was studied. Eight solvents were investigated as extractants for triterpene production in the ISEF system. The results showed that using vegetable oil as an extractant significantly increased the yield of total triterpenes and biomass of S. vaninii YC-1, reaching 18.98 ± 0.71 and 44.67 ± 2.21 g/L, respectively. In 5 L fermenter experiments, the added vegetable oil improved the dissolved oxygen condition of the fermentation broth and promoted the growth of S. vaninii YC-1. Furthermore, adding vegetable oil increased the expression of fatty acid synthesis-related genes such as FAD2 and SCD, thereby increasing the synthesis of unsaturated fatty acids in the cell membrane of S. vaninii YC-1. Therefore, the cell membrane permeability of S. vaninii YC-1 increased by 19%. Our results indicated that vegetable oil increased the permeability of S. vaninii YC-1 cell membranes to promote the production of total triterpenes. The use of vegetable oil as an extractant was thus effective in increasing the yield of triterpenes in the ISEF system.

A new endophyte Monascus ruber SRZ112 as an efficient production platform of natural pigments using agro-industrial wastes

A number of biopigment applications in various industrial sectors are gaining importance due to the growing consumer interest in their natural origin. Thus, this work was conducted to valorize endophytic fungi as an efficient production platform for natural pigments. A promising strain isolated from leaves of Origanum majorana was identified as Monascus ruber SRZ112 produced several types of pigments. The nature of the pigments, mainly rubropunctamine, monascin, ankaflavin, rubropunctatin, and monascorubrin in the fungal extract was studied by LC/ESI–MS/MS analyses. As a first step towards developing an efficient production of red pigments, the suitability of seven types of agro-industrial waste was evaluated. The highest yield of red pigments was obtained using potato peel moistened with mineral salt broth as a culture medium. To increase yield of red pigments, favourable culture conditions including incubation temperature, incubation period, pH of moistening agent, inoculum concentration, substrate weight and moisture level were evaluated. Additionally, yield of red pigments was intensified after the exposure of M. ruber SRZ112 spores to 1.00 KGy gamma rays. The final yield was improved by a 22.12-fold increase from 23.55 to 3351.87 AU g⁻¹. The anticancer and antioxidant properties of the pigment’s extract from the fungal culture were also studied. The obtained data indicated activity of the extract against human breast cancer cell lines with no significant cytotoxicity against normal cell lines. The extract also showed a free radical scavenging potential. This is the first report, to our knowledge, on the isolation of the endophytic M. ruber SRZ112 strain with the successful production of natural pigments under solid-state fermentation using potato peel as a substrate.

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

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

A review on mycelial pellets as biological carriers: Wastewater treatment and recovery for resource and energy

Mycelial pellets, a new environment friendly biological carrier, have received wide attention from researchers due to porosity, stability and unique biocompatibility. In this article, the theoretical basis and mechanism of mycelial pellets as a biological carrier were analyzed from the properties of mycelial pellets and the interaction between mycelial pellets and other microorganisms. This article aims to collate and present the current application and development trend of mycelial pellets as biological carriers in wastewater treatment, resource and energy recovery, especially the symbiotic particle system formed by mycelial pellets and microalgae is an important way to break through the technical bottleneck of biodiesel recovery from wastewater. This review also analyzes the research hotspots and trends of mycelial pellets as carriers in recent years, discusses the challenges faced by this technology, and puts forward corresponding solutions.

Increased Water-Soluble Yellow Monascus Pigment Productivity via Dual Mutagenesis and Submerged Repeated-Batch Fermentation of Monascus purpureus

Monascus pigments (MPs) have been used in the food industry for more than 2,000 years and are known for their safety, bold coloring, and physiological activity. MPs are mainly yellow (YMPs), orange (OMPs), and red (RMPs). In this study, a mutant strain Monascus purpureus H14 with high production of water-soluble YMPs (WSYMPs, λ_max at 370 nm) was generated instead of primary YMPs (λ_max at 420 nm), OMPs (λ_max at 470 nm), and RMPs (λ_max at 510 nm) produced by the parent strain M. purpureus LQ-6 through dual mutagenesis of atmospheric and room-temperature plasma and heavy ion beam irradiation (HIBI), producing 22.68 U/ml extracellular YMPs and 10.67 U/ml intracellular YMPs. WSYMP production was increased by 289.51% in optimal conditions after response surface methodology was applied in submerged fermentation. Application of combined immobilized fermentation and extractive fermentation improved productivity to 16.89 U/ml/day, 6.70 times greater than with conservative submerged fermentation. The produced WSYMPs exhibited good tone stability to environmental factors, but their pigment values were unstable to pH, light, and high concentrations of Ca²⁺, Zn²⁺, Fe²⁺, Cu²⁺, and Mg²⁺. Furtherly, the produced exYMPs were identified as two yellow monascus pigment components (monascusone B and C₂₁H₂₇NO₇S) by UHPLC-ESI-MS. This strategy may be extended to industrial production of premium WSYMPs using Monascus.

Analysis of secondary metabolite gene clusters and chitin biosynthesis pathways of Monascus purpureus with high production of pigment and citrinin based on whole-genome sequencing

Monascus is a filamentous fungus that is widely used for producing Monascus pigments in the food industry in Southeast Asia. While the development of bioinformatics has helped elucidate the molecular mechanism underlying metabolic engineering of secondary metabolite biosynthesis, the biological information on the metabolic engineering of the morphology of Monascus remains unclear. In this study, the whole genome of M. purpureus CSU-M183 strain was sequenced using combined single-molecule real-time DNA sequencing and next-generation sequencing platforms. The length of the genome assembly was 23.75 Mb in size with a GC content of 49.13%, 69 genomic contigs and encoded 7305 putative predicted genes. In addition, we identified the secondary metabolite biosynthetic gene clusters and the chitin synthesis pathway in the genome of the high pigment-producing M. purpureus CSU-M183 strain. Furthermore, it is shown that the expression levels of most Monascus pigment and citrinin clusters located genes were significantly enhanced via atmospheric room temperature plasma mutagenesis. The results provide a basis for understanding the secondary metabolite biosynthesis, and constructing the metabolic engineering of the morphology of Monascus.

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.

Cost-effective process for the production of Monascus pigments using potato pomace as carbon source by fed-batch submerged fermentation

Potato pomace, generated from starch-processing industry, was applied as a cost-effective resource for producing Monascus pigments via submerged fermentation. First, the pigment-production capacity of potato pomace and its hydrolysate was compared. The results indicated that potato pomace was superior to its hydrolysate when used for producing Monascus pigments. The red and yellow pigments produced in potato pomace medium reached 27.8 and 19.7 OD units/ml in 7 days, with the yield of total pigments at 1,187.5 OD units/g, respectively, increased by 127.9%, 19.4%, and 46.3% compared with the data obtained from hydrolysate. Meanwhile, the citrinin produced in potato pomace medium decreased by 22.6%. Afterward, potato pomace, without hydrolysis, was used as carbon source to obtain the optimal pigment production conditions. In the batch fermentation process, it was found that high amount of pomace inhibited the growth rate of mycelia and the productivity of pigments, and the fed-batch fermentation process could enhance the yield and productivity of pigments. With the same final amount of pomace (80 g/L), the maximal levels of total pigments and productivity obtained from fed-batch process reached 118.8 OD units/ml and 13.2 OD units/(ml·day), which presented an increase of 35.2% and 67.1% compared with the not fed-batch group, respectively. The results demonstrated that potato pomace was a cost-effective substrate for producing Monascus pigments in terms of pigment production capacity and productivity when fed-batch submerged fermentation was applied.

Comparative metabolomics analysis reveals the metabolic regulation mechanism of yellow pigment overproduction by Monascus using ammonium chloride as a nitrogen source

Monascus yellow pigments (MYPs), as food colorants, are of great interest to the food industry, because of their beneficial biological activities. In this study, a comparative metabolomics strategy revealed the metabolic regulatory mechanism of MYP overproduction, comparing ammonium chloride with peptone as nitrogen sources. Metabolomics-based multivariate regression modeling showed that metabolic biomarkers/modules, such as glucose, lactate, and the pentose phosphate (PP) pathway, were closely associated with the biosynthesis of MYPs. Exogenous addition of glucose increased production of MYPs, whereas lactate reduced it. Inhibition of the PP pathway with dehydroepiandrosterone decreased MYP production, while increasing the shunting production of orange and red pigments. All these treatments significantly changed the expression profiles of the pigment biosynthetic gene cluster and the mycelial morphology. Overall, this study demonstrates the feasibility of elucidating the mechanism of MYP biosynthesis by comprehensive metabolomics analysis, as well as discovering potential engineering targets of efficiency improvements to commercial MYP production. KEY POINTS: • Comparative metabolomics revealed the biomarkers/modules of MYP production. • A rational exogenously adding strategy was implemented to regulate MYP synthesis. • Expression profiles of gene cluster and mycelial morphology were characterized.

Toward improvements for enhancement the productivity and color value of Monascus pigments: a critical review with recent updates

Monascus pigments are a kind of high-quality natural edible pigments fermented by Monascus filamentous fungi, which have been widely used in food, cosmetics, medicine, textiles, dyes and chemical industries as active functional ingredients. Moreover, Monascus pigments have a good application prospect because of a variety of biological functions such as antibacterial, antioxidation, anti-inflammatory, regulating cholesterol, and anti-cancer. However, the low productivity and color value of pigments restrict their development and application. In this review, we introduced the categories, structures, biosynthesis and functions of Monascus pigments, and summarized the current methods for improving the productivity and color value of pigments, including screening and mutagenesis of strains, optimization of fermentation conditions, immobilized fermentation, mixed fermentation, additives, gene knockout and overexpression technologies, which will help to develop the foundation for the industrial production of Monascus pigments.

Colors of life: a review on fungal pigments

Colorants find social and commercial applications in cosmetics, food, pharmaceuticals, textiles, and other industrial sectors. Among the available options, chemically synthesized colorants are popular due to their low-cost and flexible production modes, but health and environmental concerns have encouraged the valorization of biopigments that are natural and ecofriendly. Among natural biopigment producers, microorganisms are noteworthy for their all-seasonal production of stable and low-cost pigments with high-yield titers. Fungi are paramount sources of natural pigments. They occupy diverse ecological niches with adaptive metabolisms and biocatalytic pathways, making them entities with an industrial interest. Industrially important biopigments like carotenoids, melanins, riboflavins, azaphilones, and quinones produced by filamentous fungi are described within the context of this review. Most recent information about fungal pigment characteristics, biochemical production routes and pathways, potential applications, limitations, and future research perspectives are described.

Evaluating the effects of microparticle addition on mycelial morphology, natural yellow pigments productivity, and key genes regulation in submerged fermentation of Monascus purpureus

Morphology plays an important role in fungal fermentation and secondary metabolites biosynthesis. One novel technique, microparticle-enhanced cultivation was successfully utilized to control the morphology of Monascus purpureus precisely and enhance the yield of yellow pigments. The production of yellow pigments increased to 554.2 U/ml when 4 g/L 5000 mesh talc added at 24 h. Field emission scanning electron microscope observation indicated that the actual effect depends on the properties of microparticle. Sharp-edged microparticles showed better stimulatory effects than smooth, round-shaped ones. Particle size analysis, scanning electron microscope, and cell integrity evaluation proved obvious morphological changes were induced by talc addition, including smaller mycelial size, rougher hyphae, and decreased cell integrity. Furthermore, the expression levels of MrpigG, MrpigD, MrpigE, and MrpigH were significantly upregulated by the addition of talc. It indicated that the microparticle could not only affect the mycelial morphology, but also influence the expression levels of key genes in biosynthetic pathway of Monascus yellow pigments.

Ammonium nitrate regulated the color characteristic changes of pigments in Monascus purpureus M9

Monascus pigments (MPs) with different color characteristics, produced by submerged fermentation of Monascus purpureus M9, have potential application in food industry. In the present study, the effects and regulatory mechanisms of ammonium nitrate (AN) on the color characteristics of MPs were investigated. The concentration of intracellular pigments was significantly decreased when subjected to AN. The hue and lightness value indicated AN altered the total pigments appearance from original red to orange. The HPLC analysis for six major components of MPs showed that the production of rubropunctatin or monascorubrin, was significantly reduced to the undetectable level, whereas the yields of monascin, ankaflavin, rubropunctamine and monascorubramine, were apparently increased with AN supplement. To be noted, via real-time quantitative PCR strategy, the expression level of mppG, closely relative to orange pigments biosynthesis, was significantly down-regulated. However, the expression of mppE, involved in yellow pigments pathway, was up-regulated. Moreover, the broth pH value was dropped to 2.5–3.5 in the fermentation process resulted from AN treatment, along with the increased extracellular polysaccharide biosynthesis. Taken together, the change of MPs categories and amounts by AN might be the driving force for the color characteristics variation in M. purpureus M9. The present study provided useful data for producing MPs with different compositions and modified color characteristics.

Biosynthesis of azaphilones: a review

Covering up to 2020 Azaphilones are fungal polyketide pigments bearing a highly oxygenated pyranoquinone bicyclic core; they are receiving a great deal of increasing research interest for their applications in the agroalimentary, dyeing, cosmetic, printing and pharmaceutical industries. Their biosynthetic pathways are not fully elucidated; however, thanks to recent genomic approaches combined with the increasing genome sequencing of fungi, some of these pathways have been recently unveiled. This is the first review on the biosynthesis of azaphilonoids adressed from a genomic point of view.

Enhancement of Monascus yellow pigments production by activating the cAMP signalling pathway in Monascus purpureus HJ11

BACKGROUND

Monascus azaphilone pigments (MonAzPs), which were produced by Monascus species, have been used as important food colorant and food supplements for more than one billion people during their daily life. Moreover, MonAzPs recently have received more attention because of their diverse physiological activities. However, the high microbial production of MonAzPs is still not always guaranteed. Herein, the aim of this study was to develop an efficient biotechnological process for MonAzPs production.

RESULTS

In this study, exogenous cyclic adenosine monophosphate (cAMP) treatment not only induced MonAzPs production, but also stimulated the expression of a cAMP phosphodiesterase gene, named as mrPDE, in M. purpureus HJ11. Subsequently, MrPDE was identified as a cAMP phosphodiesterase by in vitro enzymatic reaction with purified enzyme. Further, a gene knockout mutant of mrPDE was constructed to verify the activation of cAMP signalling pathway. Deletion of mrPDE in M. purpureus HJ11 improved cAMP concentration by 378% and enhanced PKA kinase activity 1.5-fold, indicating that activation of cAMP signalling pathway was achieved. The ΔmrPDE strain produced MonAzPs at 8563 U/g, with a 2.3-fold increase compared with the WT strain. Moreover, the NAPDH/NADP⁺ ratio of the ΔmrPDE strain was obviously higher than that of the wild type strain, which led to a higher proportion of yellow MonAzPs. With fed-batch fermentation of the ΔmrPDE strain, the production and yield of MonAzPs achieved 332.1 U/mL and 8739 U/g.

CONCLUSIONS

A engineered M. purpureus strain for high MonAzPs production was successfully developed by activating the cAMP signalling pathway. This study not only describes a novel strategy for development of MonAzPs-producing strain, but also provides a roadmap for engineering efforts towards the production of secondary metabolism in other filamentous fungi.

Microbial Colorants Production in Stirred-Tank Bioreactor and Their Incorporation in an Alternative Food Packaging Biomaterial

Natural colorants from microbial fermentation have gained significant attention in the market to replace the synthetic ones. Talaromyces spp. produce yellow-orange-red colorants, appearing as a potential microorganism to be used for this purpose. In this work, the production of natural colorants by T. amestolkiae in a stirred-tank bioreactor is studied, followed by its application as additives in bio-based films. The effect of the pH-shift control strategy from 4.5 to 8.0 after 96 h of cultivation is evaluated at 500 rpm, resulting in an improvement of natural colorant production, with this increase being more significant for the orange and red ones, both close to 4-fold. Next, the fermented broth containing the colorants is applied to the preparation of cassava starch-based films in order to incorporate functional activity in biodegradable films for food packaging. The presence of fermented broth did not affect the water activity and total solids of biodegradable films as compared with the standard one. In the end, the films are used to pack butter samples (for 45 days) showing excellent results regarding antioxidant activity. It is demonstrated that the presence of natural colorants is obtained by a biotechnology process, which can provide protection against oxidative action, as well as be a functional food additive in food packing biomaterials.

Improving mycelial morphology and adherent growth as well as metabolism of Monascus yellow pigments using nitrate resources

Mycelial adhesion affects cell growth and the production of water-soluble extracellular yellow pigment (EYP) in submerged fermentation with Monascus ruber CGMCC 10910. Two nitrates, NaNO₃ and KNO₃, were used as nitrogen sources for mitigating mycelial adhesion and improving the production of EYP in this study. The results showed that the adhesion of mycelia in the fermentation broth significantly decreased by adding 5 g/L NaNO₃, which prevented mycelia from attaching to the inner wall of the Erlenmeyer flask. It was suggested that NaNO₃ reduced the total amount of extracellular polysaccharides, increased extracellular proteins, and decreased the viscosity of the fermentation broth. Scanning electron microscopy (SEM) analysis revealed that the mycelial morphology was shorter and more dispersed and vigorous under NaNO₃ conditions than under the control conditions. The biomass increased by 49.2% and 45.4% with 5 g/L NaNO₃ and 6 g/L KNO₃ treatment, respectively, compared with that of the control, and the maximum production of EYP was 267.1 and 241.8 AU₃₅₀, which increased by 70.0% and 53.9% compared with that of the control, respectively. Simultaneously, the ratios of intracellular yellow pigment to orange pigment increased significantly with 5 g/L of NaNO₃ addition (p < 0.05). Genetic analysis found that the expression levels of the key genes for Monascus pigment biosynthesis were significantly upregulated by NaNO₃ addition (p < 0.05 or p < 0.01). This study provides an effective strategy for the production of water-soluble Monascus yellow pigments.Key Points• Nitrate addition decreased mycelial adhesion and improved cell growth in Monascus pigment fermentation.• The biosynthesis genes of water-soluble extracellular yellow pigment (EYP) were upregulated by nitrate addition.• The mycelial morphology was significantly influenced to enhance EYP biosynthesis with nitrate addition.

Production and characterization of okara dietary fiber produced by fermentation with Monascus anka

Okara dietary fiber was prepared by liquid fermentation with Monascus anka (M. anka). Infrared spectra results indicated that there were more oligosaccharides because of the hydrogen bond cleavage of the polysaccharides in okara Monascus dietary fiber (OMDF). Scanning electron microscopy and X-ray analyses showed that the structures of OMDF were altered as compared to that of the control. The UV-visible spectrum of the M. anka seed broth (MSB) contained three absorption peaks corresponding to red, orange, and yellow pigments, which were present in equal quantities. The concentration of citrinin in MSB and Monascus okara fermentation broth was 0.980 ppm and 0.940 ppm, respectively. After fermentation, the soluble OMDF content in OMDF was 7.7 g/100 g, which was 1.79 times of that in the control. Further, the water holding capacity, oil holding capacity, and swelling capacity of OMDF increased significantly, while the water retaining capacity decreased slightly. HYPOTHESIS: This study was aimed at investigating the effect of liquid fermentation of M. anka on okara. After fermentation, the dietary fiber structure may change and the functional properties may be improved.

Effects of pigment and citrinin biosynthesis on the metabolism and morphology of Monascus purpureus in submerged fermentation

The effects of the secondary metabolite biosynthesis on the metabolism and morphology of the Monascus purpureus were investigated in this study. Hypha and septum length became longer after deletion of genes pigR and pksCT in M. purpureus LQ-6 by Agrobacterium tumefaciens-mediated transformation technology, highly branched hyphae, much smaller and freely dispersed mycelial pellets were observed in M. purpureus. Compared with that in the wild-type, the level of intracellular NADH and NADPH was almost constant in M. purpureus ΔpigR at 4 days, but the NADH and NADPH levels decreased by 1.58-fold and 3.71-fold in M. purpureus ΔpksCT. The present study can not only provide a kind of strategy to improve the Monascus pigments production, but also provide theoretical support for the further study of relationship between the secondary metabolites, metabolism and morphological change.

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.

Pigment Production by the Edible Filamentous Fungus Neurospora Intermedia

The production of pigments by edible filamentous fungi is gaining attention as a result of the increased interest in natural sources with added functionality in the food, feed, cosmetic, pharmaceutical and textile industries. The filamentous fungus Neurospora intermedia, used for production of the Indonesian food “oncom”, is one potential source of pigments. The objective of the study was to evaluate the fungus’ pigment production. The joint effect from different factors (carbon and nitrogen source, ZnCl2, MgCl2 and MnCl2) on pigment production by N. intermedia is reported for the first time. The scale-up to 4.5 L bubble column bioreactors was also performed to investigate the effect of pH and aeration. Pigment production of the fungus was successfully manipulated by varying several factors. The results showed that the formation of pigments was strongly influenced by light, carbon, pH, the co-factor Zn2+ and first- to fourth-order interactions between factors. The highest pigmentation (1.19 ± 0.08 mg carotenoids/g dry weight biomass) was achieved in a bubble column reactor. This study provides important insights into pigmentation of this biotechnologically important fungus and lays a foundation for future utilizations of N. intermedia for pigment production.

Efficient Biosynthesis of Natural Yellow Pigments by Monascus purpureus in a Novel Integrated Fermentation System

Because of the increasing demand for healthy and safe food, Monascus spp. have gained much attention as a sustainable source of natural food colorant. In this study, a novel integrated fermentation system consisting of surfactant and in situ extractant was established for efficiently producing yellow pigments by M. purpureus sjs-6. The maximum production of Monascus yellow pigment (669.2 U/mL) was obtained when 40% soybean oil (as extractant) was supplied at the beginning and 5 g/L Span-80 (as surfactant) was supplied at the 72nd h, which resulted in production 27.8-times of that of the control. Critical factors such as alleviating the product inhibition, increasing the membrane permeability, changing the hyphal morphology, and influencing the cell activity have been suggested as the underlying mechanisms. This system is of great significance for the bioprocess, which suffers product inhibition, and it can serve as a promising step for enhancing the yield of hydrophobic metabolites.

Changing oxidoreduction potential to improve water-soluble yellow pigment production with Monascus ruber CGMCC 10910

Background

Monascus pigments are widely used in the food and pharmaceutical industries due to their safety to human health. Our previous study found that glucose concentration induced extracellular oxidoreduction potential (ORP) changes could influence extracellular water-soluble yellow pigment production by Monascus ruber CGMCC 10910 in submerged fermentation. In this study, H₂O₂ and dithiothreitol (DTT) were used to change the oxidoreduction potential for investigating the effects of oxidative or reductive substances on Monascus yellow pigment production by Monascus ruber CGMCC 10910.

Results

The extracellular ORP could be controlled by H₂O₂ and DTT. Both cell growth and extracellular water-soluble yellow pigment production were enhanced under H₂O₂-induced oxidative (HIO) conditions and were inhibited under dithiothreitol-induced reductive conditions. By optimizing the amount of H₂O₂ added and the timing of the addition, the yield of extracellular water-soluble yellow pigments significantly increased and reached a maximum of 209 AU, when 10 mM H₂O₂ was added on the 3rd day of fermentation with M. ruber CGMCC 10910. Under HIO conditions, the ratio of NADH/NAD+ was much lower than that in the control group, and the expression levels of relative pigment biosynthesis genes were up-regulated; moreover, the activity of glucose-6-phosphate dehydrogenase (G6PDH) was increased while 6-phosphofructokinase (PFK) activity was inhibited.

Conclusions

Oxidative conditions induced by H₂O₂ increased water-soluble yellow pigment accumulation via up-regulation of the expression levels of relative genes and by increasing the precursors of pigment biosynthesis through redirection of metabolic flux. In contrast, reductive conditions induced by dithiothreitol inhibited yellow pigment accumulation. This experiment provides a potential strategy for improving the production of Monascus yellow pigments.

Electronic supplementary material

The online version of this article (10.1186/s12934-017-0828-0) contains supplementary material, which is available to authorized users.