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

Phospholipid biosynthesis regulation for improving pigment production by Monascus in response to ammonium chloride stress

In the actual industrial production process, the efficient biosynthesis and secretion of Monascus pigments (MPs) tend to take place under abiotic stresses, which often result in an imbalance of cell homeostasis. The present study aimed to thoroughly describe the changes in lipid profiles in Monascus purpureus by absolute quantitative lipidomics and tandem mass tag-based quantitative proteomics. The results showed that ammonium chloride stress (15 g/L) increased MP production while inhibiting ergosterol biosynthesis, leading to an imbalance in membrane lipid homeostasis in Monascus. In response to the imbalance of lipid homeostasis, the regulation mechanism of phospholipids in Monascus was implemented, including the inhibition of lysophospholipids production, maintenance of the ratio of PC/PE, and improvement of the biosynthesis of phosphatidylglycerol, phosphatidylserine, and cardiolipin with high saturated and long carbon chain fatty acids through the CDP-DG pathway rather than the Kennedy pathway. The inhibition of lysophospholipid biosynthesis was attributed to the upregulated expression of protein and its gene related to lysophospholipase NTE1, while maintenance of the PC/PE ratio was achieved by the upregulated expression of protein and its gene related to CTP: phosphoethanolamine cytidylyltransferase and phosphatidylethanolamine N-methyltransferase in the Kennedy pathway. These findings provide insights into the regulation mechanism of MP biosynthesis from new perspectives.IMPORTANCEMonascus is important in food microbiology as it produces natural colorants known as Monascus pigments (MPs). The industrial production of MPs has been achieved by liquid fermentation, in which the nitrogen source (especially ammonium chloride) is a key nutritional parameter. Previous studies have investigated the regulatory mechanisms of substance and energy metabolism, as well as the cross-protective mechanisms in Monascus in response to ammonium chloride stress. Our research in this work demonstrated that ammonium chloride stress also caused an imbalance of membrane lipid homeostasis in Monascus due to the inhibition of ergosterol biosynthesis. We found that the regulation mechanism of phospholipids in Monascus was implemented, including inhibition of lysophospholipids production, maintenance of the ratio of PC/PE, and improvement of biosynthesis of phosphatidylglycerol, phosphatidylserine, and cardiolipin with high saturated and long carbon chain fatty acids through the CDP-DG pathway. These findings further refine the regulatory mechanisms of MP production and secretion.

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.

Regulation mechanism of lipids for extracellular yellow pigments production by Monascus purpureus BWY-5

The biosynthesis and secretion of Monascus pigments are closely related to the integrity of the cell membrane, which determines the composition of lipids and its content in cell membrane. The present study aimed to thoroughly describe the changes of lipid profiling in Monascus purpureus BWY-5, which was screened by carbon ion beam irradiation (¹²C⁶⁺) to almost single yield extracellular Monascus yellow pigments (extra-MYPs), by absolute quantitative lipidomics and tandem mass tags (TMT) based quantitative proteomic. ¹²C⁶⁺ irradiation caused non-lipid oxidation damage to Monascus cell membrane, leading to an imbalance in cell membrane lipid homeostasis. This imbalance was attributed to significant changes not only in the composition but also in the content of lipids in Monascus, especially the inhibition of glycerophospholipid biosynthesis. Integrity of plasma membrane was maintained by the increased production of ergosterol, monogalactosylmonoacylglycerol (MGMG) and sulfoquinovosylmonoacylglycerol (SQMG), while mitochondrial membrane homeostasis was maintained by the increase of cardiolipin production. The growth and extra-MYPs production of Monascus BWY-5 have been regulated by the promotion of sphingolipids (ceramide and sulfatide) biosynthesis. Simultaneous, energy homeostasis may be achieved by increase of TG synthesis and Ca²⁺/Mg²⁺-ATPase activity. These finding suggest ergosterol, cardiolipin, sphingolipids, MGMG and SQMG play a key facilitating role in cytomembrane lipid homeostasis maintaining for Monascus purpureus BWY-5, and then it is closely related to cell growth and extra-MYPs production. KEY POINTS: 1. Energy homeostasis in Monascus purpureus BWY-5 was achieved by increase of TG synthesis and Ca²⁺/Mg²⁺-ATPase activity. 2. Integrity of plasma membrane in Monascus purpureus BWY-5 was maintained by the increased production of ergosterol. 3. Mitochondrial membrane homeostasis in Monascus purpureus BWY-5 was maintaed by the increase of cardiolipin synthesis.

-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.

Metabolomics Analysis Coupled with Weighted Gene Co-Expression Network Analysis Unravels the Associations of Tricarboxylic Acid Cycle-Intermediates with Edible Pigments Produced by Monascus purpureus (Hong Qu)

Monascus azaphilones pigments (MonAzPs) produced by microbial fermentation are widely used as food chemicals for coloring and supplying beneficial biological attributes. In this study, a fermentation perturbation strategy was implemented by separately adding different amino acids, and detecting the intracellular metabolome via UHPLC-Q-Orbitrap HRMS. With the aid of weighted gene co-expression network analysis, two metabolic intermediates, fumarate and malate, involved in the tricarboxylic acid cycle, were identified as the hub metabolites. Moreover, exogenous addition of fumarate or malate significantly promoted red pigment production, and reduced orange/yellow pigment production. The importance of the tricarboxylic acid cycle was further emphasized by detecting intracellular levels of ATP, NAD(P)H, and expression of oxidoreductase-coding genes located in the MonAzPs synthetic gene cluster, suggesting a considerable effect of the energy supply on MonAzPs synthesis. Collectively, metabolomics is a powerful approach to position the crucial metabolic regulatory factors, and facilitate the development of engineering strategies for targeted regulation, lower trial-and-error cost, and advance safe and controllable processes for fermented food chemistry industries.

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.

Role of the Gene ndufs8 Located in Respiratory Complex I from Monascus purpureus in the Cell Growth and Secondary Metabolites Biosynthesis

Our previous work revealed that the anabolism of Monascus secondary metabolites is closely related to cofactor metabolism. In this study, we have further investigated the regulation mechanisms of respiratory complex I in response to the cell growth and secondary metabolite biosynthesis of M. purpureus. The results showed that downregulating the mRNA level of gene ndufs8 in M. purpureus sharply increased the secondary metabolites biosynthesis, cell growth and glucose consumption rates at the fermentation metaphase; slightly increased the colony diameter and biomass, and dramatically changed the mycelia morphology; and decreased the tolerances to environmental factors (especially H₂O₂). It also significantly inhibited the enzymes activities of respiratory complex I, III and superoxide dismutase, but stimulated that of complex II, IV and peroxidase, leading to an increase in reactive oxygen species (ROS) level and a decrease in ATP concentration. Furthermore, transcriptome analysis revealed that the mRNA levels of genes involved in respiratory chain, tricarboxylic acid cycle, and fatty acid degradation were downregulated, but those in the citrinin and monascus pigment biosynthesis and related pathways were upregulated. These data revealed that complex I plays a vital role in regulating the cell growth and secondary metabolism of Monascus via changing the intracellular ROS and ATP levels.

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

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

Integrative Metabolomic and Transcriptomic Analyses Uncover Metabolic Alterations and Pigment Diversity in Monascus in Response to Different Nitrogen Sources

Nitrogen in different chemical forms is critical for metabolic alterations in Monascus strains and associated pigment diversity. In this study, we observed that ammonium-form nitrogen was superior in promoting the biosynthesis of Monascus pigments (MPs) when compared with nitrate and organic forms. Moreover, with any nitrogen source, the production of yellow and orange pigments was highly synchronized but distantly related to red pigments. However, transcriptional analyses of MP gene clusters suggested a low contribution to MP accumulation, suggesting that MP-limiting factors were located outside the gene cluster. Our metabolomic analyses demonstrated that red pigment biosynthesis was closely related to intracellular amino acids, whereas orange and yellow pigments were associated with nucleotides. In addition, weighted gene coexpression network analyses (WGCNA) based on transcriptomic data showed that multiple primary metabolic pathways were closely related to red pigment production, while several secondary pathways were related to orange pigments, and others were involved with yellow pigment regulation. These findings demonstrate that pigment diversity in Monascus is under combined regulation at metabolomic and transcriptomic levels. IMPORTANCE Natural MPs containing a mixture of red, orange, and yellow pigments are widely used as food coloring agents. MP diversity provides foods with versatile colors and health benefits but, in turn, complicate efforts to achieve maximum yield or desirable combination of pigments during the manufacturing process. Apart from the MP biosynthetic gene cluster, interactions between the main biosynthetic pathways and other intracellular genes/metabolites are critical to our understanding of MP differentiation. The integrative multiomics analytical strategy provides a technical platform and new perspectives for the identification of metabolic shunting mechanisms in MP biosynthesis. Equally, our research highlights the influence of intracellular metabolic alterations on MP differentiation, which will facilitate the rational engineering and optimization of MP production in the future.

Sodium starch octenyl succinate facilitated the production of water-soluble yellow pigments in Monascus ruber fermentation

Natural water-soluble Monascus pigments (WSMPs) have been in increasing demand but have not been able to achieve industrial production due to the low production rate. This study aimed to improve the biosynthesis and secretion of extracellular yellow pigments (EYPs) through submerged fermentation with Monascus ruber CGMCC 10,910 supplemented with sodium starch octenyl succinate (OSA-SNa). The results demonstrated that the yield was 69.68% and 48.89% higher than that without OSA-SNa in conventional fermentation (CF) and extractive fermentation (EF), respectively. The mainly increased EYP components were Y3 and Y4 in CF, but they were mainly Y1 and Y2 as well as secreted intracellular pigments, including Y5, Y6, O1, and O2, in EF. Scanning electron microscopy analysis revealed that the mycelium presented an uneven surface profile with obvious wrinkles and small fragments with OSA-SNa. It was found that a higher unsaturated/saturated fatty acids ratio in the cell membrane resulted in increased permeability and facilitated the export of intracellular yellow pigments into the broth with OSA-SNa treatment. In addition, a higher NAD⁺/NADH ratio and glucose-6-phosphate dehydrogenase activity provided a reducing condition for yellow pigment biosynthesis. Gene expression analysis showed that the expression levels of the key genes for yellow pigment biosynthesis were significantly upregulated by OSA-SNa. This study provides an effective strategy to promote the production of WSMPs by microparticle-enhanced cultivation using OSA-SNa. KEY POINTS: • OSA-SNa addition facilitated the production of Monascus yellow pigments. • Mycelial morphology and membrane permeability were affected by OSA-SNa. • The key gene expression of yellow pigments was upregulated.

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.

Inducing red pigment and inhibiting citrinin production by adding lanthanum(III) ion in Monascus purpureus fermentation

Monascus pigments (MPs) are widely used natural colorants in Asian countries. The problems of low extracellular red pigment (ERP) and high citrinin remain to be solved in Monascus pigment production. The effect of lanthanum(III) ion (LaCl₃) on Monascus purpureus fermentation was investigated in this study. The yields of ERP and biomass respectively reached maxima of 124.10 U/mL and 33.10 g/L by adding 0.4 g/L La³⁺ on the second day in the total 8-day fermentation; simultaneously, citrinin was decreased by 59.93% and 38.14% in the extracellular and intracellular fractions, respectively. Reactive oxygen species (ROS) levels were obviously improved by La³⁺ treatment, while the activities of catalase (CAT) and superoxide dismutase (SOD) were increased compared with the control. The ratio of unsaturated/saturated fatty acids in mycelia was increased from 2.94 to 3.49, indicating that the permeability and fluidity of the cell membrane were enhanced under La³⁺ treatment. Gene expression analysis showed that the relative expression levels of Monascus pigment synthesis genes (pksPT, mppB, mppD, MpFasB2, and MpPKS5) were significantly upregulated by La³⁺ treatment, and in contrast, the relative expression levels of citrinin synthesis genes (ctnA, pksCT and mppC) were markedly downregulated. This work confirmed that LaCl₃ possesses the potential to induce red pigment biosynthesis and inhibit citrinin production in M. purpureus fermentation. KEY POINTS: • La³⁺ induced red pigment and inhibited citrinin production in Monascus fermentation. • La³⁺ regulated genes expression up for Monascus pigment and down for citrinin. • La³⁺ increased the UFAs in cell membrane to enhance the permeability and fluidity.

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.

Regulation of secondary metabolite biosynthesis in Monascus purpureus via cofactor metabolic engineering strategies

This study investigated the effects of cofactor metabolism on secondary metabolite production in M. purpureus through the application of different cofactor engineering strategies. Total pigment production dramatically increased by 39.08% and 40.89%, and yellow pigment production increased by 74.62% and 114.06% after the addition of 1.0 mg/L of the exogenous cofactor reagents methyl viologen and rotenone, respectively, in submerged batch-fermentation. The extracellular red pigment tone changed to yellow with the application of electrolytic stimulation at 800 mV/cm², but almost no citrinin production was detected. In addition, the total pigment, yellow pigment and citrinin production increased by 35.46%, 54.89% and 6.27% after disruption of the nuoⅠ gene that encodes NADH-quinone oxidoreductase, respectively. Thus, cofactor metabolic engineering strategies could be extended to the industrial production of Monascus pigment or high yellow pigment with free citrinin production.

Petunidin-Based Anthocyanin Relieves Oxygen Stress in Lactobacillus plantarum ST-III

Application of probiotics in the food industry has been hampered by their sensitivity to challenging conditions that reduce their vitality in food matrices. A lot of attempts have been made to promote the growth of these probiotics in the aspect of nutrition demands. Among the other adverse conditions, oxygen stress can restrict the growth of probiotics and has not yet been paid enough attention to. In this study, the effect of a petunidin-based anthocyanin (ACN) on the growth of probiotic Lactobacillus plantarum ST-III was investigated under oxygen stress. The growth of ST-III was analyzed through spot assay on agar plates as well as plating-based enumeration of the viable cells in the liquid culture. Results indicated that ACN could efficiently improve the growth of ST-III under oxygen stress, whereas no effect was observed in the absence of oxygen stress. Further investigations indicated that ACN reduced the oxido-reduction potential of the culture; meanwhile, it exerted a positive transcriptional regulation on the thioredoxin system of ST-III, leading to a decrease in reactive oxygen species accumulation within the cells. Moreover, ACN enabled the growth of ST-III in reconstituted skim milk and promoted the formation of milk clots. These results revealed the role of a petunidin-based ACN in oxygen stress relief and highlighted its potential in manufacture and preservation of L. plantarum-based dairy products.

Importance of consideration of oxidoreduction potential as a critical quality parameter in food industries

There are many intrinsic and extrinsic factors affecting the nutritional, organoleptic, microbial-enzymatic and physicochemical characteristics of food products. Some of these factors are commonly considered by food processors such as the temperature, water activity, pH, dissolved oxygen and chemical composition, while others are less considered such as the oxidoreduction potential (E_h). This latter factor is an intrinsic electrochemical parameter expressing the tendency of the substance/medium to give or receive electrons. Contrary to what is expected, the important role of E_h is not limited to inorganic chemistry, metallic chemistry, natural water, and wastewater treatment fields but it also covers many domains in biology such as metabolic engineering, enzymatic functions, food safety, and biotechnology. Unfortunately, although the critical roles of E_h in several key reactions occurred in biological media such as food and biotechnological products, its application or controlling is still uncommon or mis-considered by food processors. The lack of specific studies and reviews concerning the E_h and its influences on the quality parameters of products could be a reason for this lack of interest from the side of food processors. Recent studies reported the potential application of this parameter in novel food processing techniques such as reducing atmosphere drying (RAD) of food products and reducing atmosphere packaging (RAP) of fresh food products for preserving the quality attributes and extending the shelf-life of food products. This paper aims to help the technical and operational personnel working in food industry sectors as well as the scientific community to have an updated and a comprehensible review about the E_h parameter permitting its consideration for potential applications in food industries.

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.

Enhanced Production of 2-Hydroxyphenazine from Glycerol by a Two-Stage Fermentation Strategy in Pseudomonas chlororaphis GP72AN

2-Hydroxyphenazine (2-OH-PHZ) is an effective biocontrol antibiotic secreted by Pseudomonas chlororaphis GP72AN and is transformed from phenazine-1-carboxylic acid (PCA). PCA is the main component of the recently registered biopesticide "Shenqinmycin". Previous research showed that 2-OH-PHZ was better in controlling wheat take-all disease than PCA; however, 2-OH-PHZ production was low under natural conditions. Herein, we confirmed that PCA induced reactive oxygen species in its host P. chlororaphis GP72AN and that the addition of DTT improved PCA production by 1.8-fold, whereas the supplementation of K₃[Fe(CN)₆] and H₂O₂ increased the conversion rate of PCA to 2-OH-PHZ. Finally, a two-stage fermentation strategy combining the addition of DTT at 12 h and H₂O₂ at 24 h enhanced 2-OH-PHZ production. Taken together, the two-stage fermentation strategy was designed to enhance 2-OH-PHZ production for the first time, and it provided a valuable reference for the fermentation of other antibiotics.

Cost-effective pigment production by Monascus purpureus using rice straw hydrolysate as substrate in submerged fermentation

Monascus pigments (MPs), the secondary metabolites produced by the fungal strains of Monascus spp., hold commercial importance in not only the food and meat industries, but also therapeutic, cosmetic, and textile industries. To reduce the cost of MPs production, the utilization of rice straw hydrolysate as a substrate in submerged fermentation was investigated. The atmospheric and room temperature plasma (ARTP) mutation system was employed to develop a mutant strain Monascus purpureus M630, with high total extracellular Monascus pigments (exMPs) production of 34.12 U/mL in submerged fermentation with glucose-based medium. The results revealed that M. purpureus M630 produces 8.61 U/mL and 20.86 U/mL of exMPs in rice straw hydrolysate alone or in combination with glucose fermentation medium, respectively. Furfural (Fur) and 5'-hydroxymethyl furfural (5'-HMF), produced during pretreatment and hydrolysis of rice straw; are generally inhibitory for microbial growth and fermentation. Our findings revealed that M. purpureus M630 develops the tolerance and adaptation mechanisms in response to 5'-HMF and Fur during growth and MPs biosynthesis in rice straw hydrolysate. In conclusion, we report that rice straw hydrolysate can serve as an efficient and low-cost substitute for the MP production through submerged fermentation by Monascus spp.

Whole-Genome Sequence of Monascus purpureus GB-01, an Industrial Strain for Food Colorant Production

We report the draft genome sequence of Monascus purpureus GB-01, an industrial strain used as a food colorant. De novo assembly of long reads resulted in 121 chromosomal contigs and 1 mitochondrial contig, and sequencing errors were corrected by paired-end short reads. This genome sequence will provide useful information for azaphilone pigments and mycotoxin citrinin biosynthesis.

Shifting product spectrum by pH adjustment during long-term continuous anaerobic fermentation of food waste

Anaerobic fermentation is widely used to recover different products from food waste, and in this study, the evolution of fermentation products and microbial community along with pH variation was investigated thoroughly using four long-term reactors. Lactic fermentation dominated the system at pH 3.2-4.5 with lactic acid concentration of 5.7-13.5 g/L, and Lactobacillus was the superior sort. Bifidobacteria increased significantly at pH 4.5, resulting in the increase of acetic acid. Butyric acid fermentation was observed at pH 4.7-5.0. Bifidobacterium, Lactobacillus, and Olsenella were still dominant, but the lactic acid produced by them was converted to volatile fatty acids (VFAs) rapidly by Megasphaera, Caproiciproducens, Solobacteria, etc. Mixed acid fermentation occurred at pH 6.0 with the highest concentration 14.2 g/L of VFAs, and the dominant Prevotella and Megasphaera converted substrates to VFAs directly. On the whole, pH 4.5 and 4.7 led to the highest hydrolysis rate of 50% and acidification rate of 45%.