Complete genome sequence and transcriptomics analyses reveal pigment biosynthesis and regulatory mechanisms in an industrial strain, Monascus purpureus YY-1

Effect of initial pH, different nitrogen sources, and cultivation time on the production of yellow or orange Monascus purpureus pigments and the mycotoxin citrinin

Monascus purpureus was grown in submerged liquid culture using ammonium sulfate, sodium nitrate, and peptone as nitrogen sources while initial medium pH was adjusted to 2.5, 5.5, 6.5, or 8.0. The combined effect of culture pH and nitrogen source on the biosynthesis of yellow (ankaflavin and monascin) and orange (rubropunctatin and monascorubrin) pigments, plus the mycotoxin citrinin, was evaluated chromatographically. Optimum cultivation conditions, that is, initial pH 2.5 and 8.8 g/L peptone as a nitrogen source, resulted in high levels of production of yellow and orange pigments (sum of pigment concentration 1,138 mg/L) and negligible citrinin concentration (2 mg/L).

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.

Nature and nurture: confluence of pathway determinism with metabolic and chemical serendipity diversifies Monascus azaphilone pigments

Covering: up to June 2018 Understanding the biosynthetic mechanisms that generate the astounding structural complexity and variety of fungal secondary metabolites (FSMs) remains a challenge. As an example, the biogenesis of the Monascus azaphilone pigments (MonAzPs) has remained obscure until recently despite the significant medical potential of these metabolites and their long history of widespread use as food colorants. However, a considerable progress has been made in recent years towards the elucidation of MonAzPs biosynthesis in various fungi. In this highlight, we correlate a unified biosynthetic pathway with the diverse structures of the 111 MonAzPs congeners reported until June 2018. We also discuss the origins of structural diversity amongst MonAzPs analogues and summarize new research directions towards exploring novel MonAzPs. The case of MonAzPs illuminates the various ways that FSMs metabolic complexity emerges by the interplay of biosynthetic pathway determinism with metabolic and chemical serendipity.

Highly efficient improvement of Monascus pigment production by accelerating starch hydrolysis in Monascus ruber CICC41233

To investigate the relationship between starch hydrolysis and Monascus pigments (MPs) production, the α-amylase gene (AOamyA) from Aspergillus oryzae was heterologously expressed in Monascus ruber CICC41233, and we obtained a positive transformant named Monascus ruber Amy9. In M. ruber Amy9, the α-amylase activities were 6.65- and 4.26-fold higher at 72 h and 144 h, respectively, than those in the parent strain with the glucose as solo carbon medium. Surprisingly, in the MPs fermentation medium with rice powder as solo material, M. ruber Amy9 completely degraded starch at 48 h, while 43.93 and 7.29 mg/mL starch remained at 48 and 144 h, respectively, in the parent strain. Monascus ruber Amy9 accelerated starch hydrolysis, which enhanced biomass and also increased total MPs by 132% after 144 h. Compared with M. ruber CICC41233, the relative gene expression levels, as determined by a quantitative real-time polymerase chain reaction analysis, of acl2 encoding ATP-citrate lyase subunit 2, pks encoding polyketide synthase, and fasB encoding the fatty acid synthase beta subunit increased by 33.14, 145.18, and 32.15%, respectively, after 144 h in M. ruber Amy9. The up-regulated expression of these key genes in MPs synthesis contributed to the large increase in MPs production. This interesting work provided us with a new idea and a new target for the study of the MPs production.

Investigation of Citrinin and Pigment Biosynthesis Mechanisms in Monascus purpureus by Transcriptomic Analysis

Monascus purpureus YY-1 is widely used in food colorant production in China. Our previous study clearly illustrated the whole-genome data for YY-1 and provided useful insight into evolutionary research and industrial applications. However, the presence of citrinin, which has nephrotoxic, hepatotoxic, and carcinogenic activities, has attracted attention to the safety of Monascus products. In an effort to reduce the harmful effects of citrinin in Monascus-related products, a random mutant of M. purpureus YY-1 with low citrinin production (designated as "winter") was obtained in this study. To analyze the biosynthesis and regulation mechanisms of pigment and citrinin, a transcriptomic analysis of the M. purpureus YY-1 and winter strains was performed. Comparative transcriptomic analysis reveals pksCT, the essential gene for citrinin synthesis, showed a low expression level in M. purpureus YY-1 and winter, which suggested there might be isoenzymes in M. purpureus YY-1 that were responsible for the citrinin synthesis during evolution. In addition, changes in transcription factor expression may also influence the network regulating the citrinin synthesis pathway in M. purpureus. Moreover, the yields of pigments produced by the winter mutant were significantly increased. Repressing the central carbon metabolism and improving the acetyl-CoA pool can contribute to a high pigment yield, and enhanced NADPH regeneration can also lead to the metabolic flux of pigment production in M. purpureus. Investigations into the biosynthesis and regulation of citrinin and pigment production in M. purpureus will enhance our knowledge of the mechanisms behind the biosynthesis of fungal secondary metabolites.

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.

Analyses of Monascus pigment secretion and cellular morphology in non-ionic surfactant micelle aqueous solution

Monascus pigments produced by Monascus spp. are widely used as natural food colourants. Extractive fermentation technology can facilitate the secretion of intracellular Monascus pigments into extracellular non-ionic surfactant micelle aqueous solution, so as to avoid the feedback inhibition and decomposition. In this study, behaviour of the trans-membrane secretion of Monascus pigments was investigated using morphological and spectroscopic analyses. Laser scanning confocal microscopy (LSCM) traced that pigment secretion occurred through rapid trans-membrane permeation in 4 min, with a simultaneous conversion in pigment characteristics. Approximately 50% of intracellular pigments (AU470 ) extracted to extracellular broth with 40 g l-1 Triton X-100, indicating the capacity for pigment extraction was limited by the saturation concentrations of surfactant. Scanning electron microscope (SEM) and transmission electron microscope (TEM) imaging showed some damage in the cell wall but an intact cell membrane with a slightly increased mycelial diameter. However, the physiological properties of the cell membrane, including integrity, fluorescence intensity and permeability, were altered. A diagram was provided to demonstrate the behaviour of Monascus pigment secretion induced by Triton X-100. This study lays a foundation for the further investigation of Monascus pigment metabolism and secretion in extractive fermentation.

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.

Optimization of submerged fermentation medium for citrinin-free monascin production by Monascus

Microbial fermentation of citrinin-free Monascus pigments is in favor in the development of food industry. This study investigated the influences of carbon source, nitrogen source, and mineral salts on the cell growth, monascin (MS), and citrinin (CT) production in Monascus M9. A culture medium composition was established for maximizing the production of citrinin-free MS in submerged culture, as follows: 50 g/L Japonica rice powder, 20 g/L NH₄NO₃, 3 g/L NaNO₃, 1.5 g/L KH₂PO₄, 1 g/L MgSO₄ · 7H₂O, 0.2 g/L MnSO₄. Under these conditions, no CT was detectable by high performance liquid chromatography. The yield of MS reached 14.11 mg/g, improving approximately 30% compared with before optimization.

Saturation effect and transmembrane conversion of Monascus pigment in nonionic surfactant aqueous solution

Extractive fermentation in a nonionic surfactant aqueous solution provides a promising and efficient method to produce Monascus pigments. The behaviour of pigment secretion during the extractive cultivation was investigated in the present work. The results revealed that the secretion of intracellular pigment was limited by its saturation concentration in the nonionic surfactant aqueous solution. The intracellular pigment was completely extracted to the outside of the cell at a low cell density and high concentration of Triton X-100 (TX) in fermentation broth; otherwise, a restriction for pigment extraction would occur. The decrement of the intracellular orange and yellow pigments was inconsistent with the increment of extracellular pigments with an increase in the TX concentration. It could be inferred that the intracellular orange pigment was converted to extracellular yellow pigment during the transmembrane secretion process, which might be attributed to the enzyme catalysis in the non-aqueous phase solution. This study helps explain the mechanism of variation of pigment characteristic and extraction capacity in extractive fermentation.

Tracking of pigment accumulation and secretion in extractive fermentation of Monascus anka GIM 3.592

Background

Monascus pigments are promising sources for food and medicine due to their natural food-coloring functions and pharmaceutical values. The innovative technology of extractive fermentation is used to promote pigment productivity, but reports of pigment trans-membrane secretion mechanism are rare. In this study, tracking of pigment accumulation and secretion in extractive fermentation of Monascus anka GIM 3.592 was investigated.

Results

The increased vacuole size in mycelia correlated with fluorescence intensity (r > 0.85, p < 0.05), which indicates that intracellular pigments with strong fluorescence accumulated in the cytoplasmic vacuole. After adding nonionic surfactant Triton X-100, the uptake of rhodamine123 (Rh123) and 1-N-phenylnaphthylamine (NPN) and the release of K⁺ and Na⁺ rapidly increased, demonstrating that the physiological performances of the cell membrane varied upon damaging the integrity, increasing the permeability, and changing the potential. Simultaneously, the fatty acid composition also varied, which caused a weak fluidity in the membrane lipids. Therefore, the intracellular pigments embedded in Triton X-100 were secreted through the ion channels of the cell membrane. Dense, spherical pigment-surfactant micelles with an average size of 21 nm were distributed uniformly in the extraction broth. Based on the different pigment components between extractive fermentation and batch fermentation, a threefold decrease in the NAD⁺/NADH ratio in mycelia and a more than 200-fold increase in glucose-6-phosphate dehydrogenase (G6PDH) activity in extracellular broth occurred, further suggesting that a reduction reaction for pigment conversion from orange pigments to yellow pigments occurred in non-aqueous phase solution.

Conclusions

A putative model was established to track the localization of Monascus pigment accumulation and its trans-membrane secretion in extractive fermentation. This finding provides a theoretical explanation for microbial extractive fermentation of Monascus pigments, as well as other non-water-soluble products.

Electronic supplementary material

The online version of this article (doi:10.1186/s12934-017-0786-6) contains supplementary material, which is available to authorized users.

The molecular mechanisms of Monascus purpureus M9 responses to blue light based on the transcriptome analysis

Light is an important environmental factor that regulates various physiological processes of fungi. To thoroughly study the responses of Monascus to blue light, transcriptome sequencing was performed on mRNAs isolated from samples of Monascus purpureus M9 cultured under three conditions: darkness (D); exposure to blue light for 15 min/d (B15); and exposure to blue light for 60 min/d over 8 days (B60). The number of differentially expressed genes between the three pairs of samples-B15 vs D, B60 vs B15, and B60 vs D-was 1167, 1172, and 220, respectively. KEGG analysis showed the genes involved in primary metabolism including carbon and nitrogen metabolism were downregulated by B15 light treatment, whereas B15 upregulated expression of genes involved with aromatic amino acid metabolism, which associated with development, and branched chain amino acid metabolism, and fatty acid degradation, which can produce the biosynthetic precursors of pigments. When exposed to B60 conditions, genes with roles in carbohydrate metabolism and protein synthesis were upregulated as part of a stress response to blue light. Based on this study, we propose a predicted light-stimulated signal transduction pathway in Monascus. Our work is the first comprehensive investigation concerning the mechanism of Monascus responses to blue light.

Orange, red, yellow: biosynthesis of azaphilone pigments in Monascus fungi

Monascus azaphilone pigments (MonAzPs) are very widely used as food colorants, but their biosynthetic pathway has remained poorly characterized for more than half a century. In this study, the individual steps of MonAzPs biosynthesis in Monascus ruber M7 were elucidated by a combination of targeted gene knockouts, heterologous gene expression, and in vitro chemical and enzymatic reactions. This study describes the first rational engineering of MonAzPs biosynthesis and provides a roadmap for future pathway engineering efforts directed towards the selective production of the most valuable pigments and serves as a model for the biosynthesis of fungal azaphilones in general.

Alleviation of metabolic syndrome by monascin and ankaflavin: the perspective of Monascus functional foods

The metabolites of Monascus with multiple benefits are popular subjects for the development of functional foods. The yellow pigments, monascin and ankaflavin, which are the constituent metabolites of M. purpureus, M. pilosus and M. ruber, are becoming the focus of research on Monascus. Monascin and ankaflavin are azaphilone compounds with similar structures that exhibit multiple beneficial effects including anti-inflammation, anti-oxidation, anti-diabetes, immunomodulation, attenuation of Alzheimer's disease risk factor, and anti-tumorigenic effects. Monascin and ankaflavin not only possess pleiotropic bioactivities, but are also more potent than monacolin K in lowering lipid levels and have lower toxicity. Monascin and ankaflavin act as the activators of PPARγ agonist/Nrf-2 that subsequently ameliorate metabolic syndrome. Following the intensive exploration of Monascus bioactivities in recent years, the focus of research on Monascus-functional foods has shifted from whole fermented products/extracts to specific bioactive compounds. Therefore, the production of monascin and ankaflavin is an important topic with respect to Monascus-functional foods. Although several genomic studies have paved the way for understanding the production of secondary metabolites in Monascus, efforts are still required to effectively manipulate the biosynthesis of secondary metabolites with genetic engineering and/or culture techniques.

Transcriptome analysis reveals metabolic alteration due to consecutive monoculture and abiotic stress stimuli in Rehamannia glutinosa Libosch

We deeply investigated the mechanism underlying metabolic regulation in response to consecutive monoculture (replanting disease) and different abiotic stresses that unfolded the response mechanism to consecutive monoculture problem through RNA-seq analysis. The consecutive monoculture problem (CMP) resulted of complex environmental stresses mediated by multiple factors. Previous studies have noted that multiple stress factors in consecutive monoculture soils or plants severely limited the interpretation of the critical molecular mechanism, and made a predict that the specifically responding factor was autotoxic allelochemicals. To identify the specifically responding genes, we compared transcriptome changes in roots of Rehamannia glutinosa Libosch using consecutive monoculture, salt, drought, and ferulic acid as stress factors. Comparing with normal growth, 2502, 2672, 2485, and 1956 genes were differentially expressed in R. glutinosa under consecutive monoculture practice, salt, drought, and ferulic acid stress, respectively. In addition, 510 genes were specifically expressed under consecutive monoculture, which were not present under the other stress conditions. Integrating the biological and enrichment analyses of the differentially expressed genes, the result demonstrated that the plants could alter enzyme genes expression to reconstruct the complicated metabolic pathways, which used to tolerate the CMP and abiotic stresses. Furthermore, most of the affected pathway genes were closely related to secondary metabolic processes, and the influence of consecutive monoculture practice on the transcriptome genes expression profile was very similar to the profile under salt stress and then to the profile under drought stress. The outlined schematic diagram unfolded the putative signal regulation mechanism in response to the CMP. Genes that differentially up- or down-regulated under consecutive monoculture practice may play important roles in the CMP or replanting disease in R. glutinosa.

Production of water-soluble yellow pigments via high glucose stress fermentation of Monascus ruber CGMCC 10910

Monascus pigments are secondary metabolites of Monascus species and are mainly composed of yellow pigments, orange pigments and red pigments. In this study, a larger proportion of Monascus yellow pigments could be obtained through the selection of the carbon source. Hydrophilic yellow pigments can be largely produced extracellularly by Monascus ruber CGMCC 10910 under conditions of high glucose fermentation with low oxidoreduction potential (ORP). However, keeping high glucose levels later in the culture causes translation or a reduction of yellow pigment. We presume that the mechanism behind this phenomenon may be attributed to the redox level of the culture broth and the high glucose stress reaction of M. ruber CGMCC 10910 during high glucose fermentation. These yellow pigments were produced via high glucose bio-fermentation without citrinin. Therefore, these pigments can act as natural pigments for applications as food additives.

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.

The genomics of microbial domestication in the fermented food environment

Shortly after the agricultural revolution, the domestication of bacteria, yeasts, and molds, played an essential role in enhancing the stability, quality, flavor, and texture of food products. These domestication events were probably the result of human food production practices that entailed the continual recycling of isolated microbial communities in the presence of abundant agricultural food sources. We suggest that within these novel agrarian food niches the metabolic requirements of those microbes became regular and predictable resulting in rapid genomic specialization through such mechanisms as pseudogenization, genome decay, interspecific hybridization, gene duplication, and horizontal gene transfer. The ultimate result was domesticated strains of microorganisms with enhanced fermentative capacities.