NAD+-dependent HDAC inhibitor stimulates Monascus pigment production but inhibit citrinin

Exploring the multifaceted roles of histone deacetylase inhibitor vorinostat in the cell growth, mycelial morphology, pigments, and citrinin biosynthesis of Monascus purpureus

Acetylation is an important modification type of histones, which is dynamically regulated by histone acetyltransferases (HATs) and histone deacetylases (HDACs). In this study, the histone acetylation level of Monascus was enhanced through the exogenous addition of the HDACs inhibitor vorinostat, and the regulation effects of histone acetylation on cell growth and secondary metabolism were evaluated. The results demonstrated that the augmentation of histone acetylation level could slightly facilitate sugar consumption, increase biomass weight, and significantly induce noticeable morphological alterations. Furthermore, in the presence of 80 μmol/L vorinostat concentration, there was a significant reduction observed in both extracellular and intracellular Monascus pigments, citrinin productions, with decreases of 35.46%, 63.90%, and 98.33% respectively. RT-qPCR results showed that adding vorinostat resulted in the up-regulation of HAT genes and down-regulation of HDAC genes. Additionally, transcriptome analysis revealed that glycolysis, tricarboxylic acid cycle, fatty acid metabolism, cell membrane anchor-protein related genes, and biosynthetic pathways involved in ergosterol and chitin synthesis were upregulated. Conversely, the electron transport chain and genetic clusters associated with Monascus pigments and citrinin synthesis were down-regulated. These findings underscore the pivotal role of histone acetylation in regulating the cell growth and secondary metabolism of M. purpureus and extend novel perspectives on the potential applications of clinical compounds derived from this process.

Regulation of Histone Acetylation Modification on Biosynthesis of Secondary Metabolites in Fungi

The histone acetylation modification is a conservative post-translational epigenetic regulation in fungi. It includes acetylation and deacetylation at the lysine residues of histone, which are catalyzed by histone acetyltransferase (HAT) and deacetylase (HDAC), respectively. The histone acetylation modification plays crucial roles in fungal growth and development, environmental stress response, secondary metabolite (SM) biosynthesis, and pathogenicity. One of the most important roles is to regulate the gene expression that is responsible for SM biosynthesis in fungi. This mini-review summarized the regulation of histone acetylation modification by HATs and HDACs on the biosynthesis of SMs in fungi. In most cases, histone acetylation by HATs positively regulated the biosynthesis of fungal SMs, while HDACs had their negative regulations. Some HATs and HDACs were revealed to regulate fungal SM biosynthesis. Hda1 was found to be the most efficient regulator to affect the biosynthesis of SMs in fungi. The regulated fungal species were mainly from the genera of Aspergillus, Calcarisporium, Cladosporium, Fusarium, Monascus, Penicillium, and Pestalotiopsis. With the strategy of histone acetylation modification, the biosynthesis of some harmful SMs will be inhibited, while the production of useful bioactive SMs will be promoted in fungi. The subsequent research should focus on the study of regulatory mechanisms.

The Histone Deacetylase Inhibitor Trichostatin-A Modifies the Expression of Trichothecene Mycotoxin Regulatory Gene Tri5 in Fusarium graminearum

Background

Fusarium graminearum is the causal agent of Fusarium Head Blight (FHB) on wheat and produces deoxynivalenol (DON), known to cause extreme human and animal toxicosis. This species' genome contains genes involved in plant-pathogen interactions and regulated by chromatin modifications. Moreover, histone deacetylase inhibitors (HDACIs), including trichostatin A (TSA), have been employed to study gene transcription regulation because they can convert the structure of chromatin.

Objectives

The current study was designed to evaluate the effects of TSA on histone deacetylase (HDAC) and, trichodiene synthase (Tri5) gene expression in toxigenic and non-toxigenic F. graminearum isolates.

Materials and Methods

The mycelia were grown on potato dextrose broth (PDB) culture media supplemented with two concentrations of TSA and dimethyl sulfoxide (DMSO) (3 and 10 µg. mL-1) for 48 h, 72 h, and 96 h. Then, the mRNA levels were estimated via real-time quantitative reverse transcription-polymerase chain reaction (real-time qRT-PCR).

Results

We found that the levels of HADC and Tri5 varied over time and dosage in response to the use of TSA. The toxigenic isolate showed an increase in the Tri5 expression when treated with TSA, with the highest levels monitored when the concentration of the substance was 3 µg. mL-1 at 48 h. The non-toxigenic isolate also showed high levels of HDAC and Tri5 expression in the presence of TSA, but a sharp decrease in the Tri5 transcription was observed at 72 h when grown on culture media containing 10 µg. mL-1 of TSA.

Conclusion

Overall, our results suggest a mode of DON biosynthesis regulation in F. graminearum by chromatin modifications that may help us offer new strategies for tackling fungal infections.

Overexpression of MrEsa1 accelerated growth, increased ascospores yield, and the polyketide production in Monascus ruber

Esa1 has been proven to be an important histone acetyltransferase involved in the regulation of growth and metabolism. Monascus spp. with nearly 2000 years of edible history in East Asian countries can produce a variety of polyketides. It is unknown whether Esa1 plays a regulatory role in Monascus spp. In this study, we isolated the homology of histone acetyltransferase Esa1 (named MrEsa1) and constructed a mresa1-overexpressed strain. Western blot experiments showed that MrEsa1 hyperacetylated at K4 and K9 of the H3 subunit in Monascus ruber. Overexpression of mresa1 led to the larger colony diameter and increased dry cell mass; meanwhile, the conidia germination rate was significantly accelerated in the mresa1-overexpressed strain before 4 h, and the number of ascospores in the mresa1-overexpressed strain was significantly higher than that in WT. In addition, the Monascus azaphilone pigments (MonAzPs) and citrinin production of the mresa1-overexpressed strain were 1.7 and 2.4 times more than those of WT, respectively. Reverse transcription-quantitative polymerase chain reaction experiment suggested that mrpigB, mrpigH, mrpigJ, and mrpigK, involved in MonAzPs synthesis, and pksCT, mrl3, and mrl7, involved in citrinin synthesis, were upregulated in mresa1-overexpressed strain. This study provides important insights into the effect of MrEsa1 on the developmental process and the production of secondary metabolites in Monascus spp.

Recent Advances in Search of Bioactive Secondary Metabolites from Fungi Triggered by Chemical Epigenetic Modifiers

Genomic analysis has demonstrated that many fungi possess essential gene clusters for the production of previously unobserved secondary metabolites; however, these genes are normally reduced or silenced under most conditions. These cryptic biosynthetic gene clusters have become treasures of new bioactive secondary metabolites. The induction of these biosynthetic gene clusters under stress or special conditions can improve the titers of known compounds or the production of novel compounds. Among the inducing strategies, chemical-epigenetic regulation is considered a powerful approach, and it uses small-molecule epigenetic modifiers, which mainly act as the inhibitors of DNA methyltransferase, histone deacetylase, and histone acetyltransferase, to promote changes in the structure of DNA, histones, and proteasomes and to further activate cryptic biosynthetic gene clusters for the production of a wide variety of bioactive secondary metabolites. These epigenetic modifiers mainly include 5-azacytidine, suberoylanilide hydroxamic acid, suberoyl bishydroxamic acid, sodium butyrate, and nicotinamide. This review gives an overview on the method of chemical epigenetic modifiers to trigger silent or low-expressed biosynthetic pathways to yield bioactive natural products through external cues of fungi, mainly based on the research progress in the period from 2007 to 2022. The production of about 540 fungal secondary metabolites was found to be induced or enhanced by chemical epigenetic modifiers. Some of them exhibited significant biological activities such as cytotoxic, antimicrobial, anti-inflammatory, and antioxidant activity.

Inactivation of MrSir2 in Monascus ruber Influenced the Developmental Process and the Production of Monascus Azaphilone Pigments

Monascus species are the producers of Monascus azaphilone pigments (MonAzPs) and lipid-lowering component Monacolin K, which have been widely used as food colorant and health products. In this study, silent information regulator 2 (Sir2) homolog (MrSir2) was characterized, and its impacts on the development and MonAzPs production of Monascus ruber were evaluated. Enzyme activity test in vitro showed that MrSir2 was an NAD⁺-dependent histone deacetylase. Compared to WT, Δmrsir2 strain accumulated more acetylated lysine residues of histone H3 subunit during its vegetative growth phase, and it exhibited accelerated mycelial aging, more spores, increased resistance to oxidative stress, and more MonAzPs production. RNA-Seq-based transcriptome analysis revealed that MrSir2 mainly regulated the gene expression in macromolecular metabolism such as carbohydrates, proteins, and nucleotides, as well as genes encoding cell wall synthesis and cell membrane component, indicating that MrSir2 probably facilitates the metabolic transition from the primary growth phase to the mycelial aging. Taken together, MrSir2 mainly targets H3 subunit at the vegetative growth phase and affects the development of M. ruber and MonAzPs production.

Effects of some flavonoids on the mycotoxin citrinin reduction by Monascus aurantiacus Li AS3.4384 during liquid-state fermentation

Monascus can produce many beneficial metabolites; however, it can simultaneously also produce citrinin, which seriously limits its application. Therefore, reducing the production of citrinin is of great interest. Herein, Monascus aurantiacus Li AS3.4384 (MAL) was used to optimize the liquid-state fermentation process and investigate the effects of genistein and other flavonoids on citrinin, pigments, and biomass of MAL. Results showed that citrinin decreased by 80%, pigments and biomass increased by approximately 20% in 12 days with addition of 20.0 g/L rice powder as a carbon source and 2.0 g/L genistein during shaking liquid-state fermentation. Further, genistein, daidzein, luteolin, apigenin, quercetin, baicalein, kaempferol myricetin, and genistin exerted different effects on citrinin production by MAL, with genistein causing the highest reduction in citrinin production during liquid-state fermentation, possibly due to the presence of C5-OH, C4′-OH, and C7-OH. Therefore, genistein can be added to the fermentation process of Monascus to reduce citrinin.

Recent advances in the chemistry and biology of azaphilones

Recent advances in the chemistry and biology of structurally diverse azaphilones from 2012 to 2019.

Soybean isoflavones reduce citrinin production by Monascus aurantiacus Li AS3.4384 in liquid state fermentation using different media

BACKGROUND

Monascus, a filamentous fungus, produces many bioactive substances. However, in the process of fermentation, Monascus also produces the mycotoxin citrinin. Owing to the presence of citrinin, the safety of Monascus products has been questioned and their wide application limited. Using soybean isoflavones (SI) as exogenous additives, alterations in citrinin production by Monascus aurantiacus Li AS3.4384 (MALA) in different media used for liquid state fermentation were investigated.

RESULTS

Results showed that the citrinin concentration was 95.98% lower than that of the control group after 16-days fermentation when 20.0 g L-1 SI were added to rice powder and inorganic salt medium. Citrinin production was reduced by 97.24% after 12-days fermentation with 10.0 g L-1 SI in starch inorganic salt medium; 82.52% after 20-days fermentation with 20.0 g L-1 SI in starch peptone medium with high starch content; 45.07% after 14-days fermentation with 5.0 g L-1 SI in starch peptone medium with low starch content; and 82.21% after 14-days fermentation with 20.0 g L-1 SI in yeast extract sucrose medium.

CONCLUSION

The developed method of removing citrinin is simple, safe, and effective, and it can be applied to reduce the citrinin content of Monascus products. © 2019 Society of Chemical Industry.

On top of biosynthetic gene clusters: How epigenetic machinery influences secondary metabolism in fungi

Fungi produce an abundance of bioactive secondary metabolites which can be utilized as antibiotics and pharmaceutical drugs. The genes encoding secondary metabolites are contiguously arranged in biosynthetic gene clusters (BGCs), which supports co-regulation of all genes required for any one metabolite. However, an ongoing challenge to harvest this fungal wealth is the finding that many of the BGCs are 'silent' in laboratory settings and lie in heterochromatic regions of the genome. Successful approaches allowing access to these regions - in essence converting the heterochromatin covering BGCs to euchromatin - include use of epigenetic stimulants and genetic manipulation of histone modifying proteins. This review provides a comprehensive look at the chromatin remodeling proteins which have been shown to regulate secondary metabolism, the use of chemical inhibitors used to induce BGCs, and provides future perspectives on expansion of epigenetic tools and concepts to mine the fungal metabolome.

Effects of rutin and its derivatives on citrinin production by Monascus aurantiacus Li AS3.4384 in liquid fermentation using different types of media

The mycotoxin citrinin is often produced during fermentation of Monascus products. We studied the effects of flavonoids on citrinin production by Monascus aurantiacus Li AS3.4384 (MALA) by adding rutin, α-glucosylrutin, or troxerutin to the fermentation medium, in a first-of-its-kind study. Appropriate amounts of rutin, α-glucosylrutin, or troxerutin did not affect normal mycelial growth. Addition of 5.0 g/l of rutin only weakly reduced (29.2%) citrinin production, relative to inhibition by 5 g/l α-glucosylrutin or troxerutin (by 54.7% and 40.6%, respectively). In starch inorganic liquid culture media, addition of 20.0 g/l of troxerutin, followed by fermentation for 12 days, reduced citrinin yield by 75.26%. Addition of 15.0 g/l of troxerutin to low-starch peptone liquid fermentation media reduced citrinin yield by 87.9% after 14 days of fermentation, and addition of 30.0 g/l troxerutin to yeast extract sucrose liquid media for 12 days reduced citrinin yield by 53.7%.

5-Methylmellein is a novel inhibitor of fungal sirtuin and modulates fungal secondary metabolite production

Sirtuin is an NAD⁺-dependent histone deacetylase that is highly conserved among prokaryotes and eukaryotes. Sirtuin deacetylates histones and non-histone proteins, and it is involved in fungal growth and secondary metabolite production. Here, we screened 579 fungal culture extracts that inhibited the histone deacetylase activity of Sirtuin A (SirA), produced by the fungus Aspergillus nidulans. Eight fungal strains containing three Ascomycota, two Basidiomycota and three Deuteromycetes produced SirA inhibitors. We purified the SirA inhibitor from the culture broth of Didymobotryum rigidum JCM 8837, and identified it as 5-methylmellein-a known polyketide. This polyketide and its structurally-related compound, mellein, inhibited SirA activity with IC₅₀ of 120 and 160 μM, respectively. Adding 5-methylmellein to A. nidulans cultures increased secondary metabolite production in the medium. The metabolite profiles were different from those obtained by adding other sirtuin inhibitors nicotinamide and sirtinol to the culture. These results indicated that 5-methylmellein modulates fungal secondary metabolism, and is a potential tool for screening novel compounds derived from fungi.