Perylenequinones: Isolation, Synthesis, and Biological Activity

Protein kinase C (PKC) inhibitor Calphostin C activates PKC in a light-dependent manner at high concentrations via the production of singlet oxygen

Calphostin C (Cal-C) is a protein kinase C (PKC) inhibitor that binds to its C1 domain. The aim of the present study was to elucidate the action of Cal-C in addition to PKC inhibition. First, we confirmed that Cal-C at low concentrations (<200 nM) inhibit phorbol ester-induced PKC translocation and G-protein-coupled receptor (GPCR)-mediated PKC activation. Cal-C at higher concentrations (>2 μM) increased intracellular calcium ion concentrations ([Ca2+]i) in a concentration-dependent manner. The origin of this increase is the mobilization of the endoplasmic reticulum (ER), which does not involve GPCR or ryanodine receptors. Cal-C at high concentrations also cause structural changes in the ER, such as the formation of vacuoles and aggregates, and calcium leakage from the ER. At 2 μM, Cal-C translocated a calcium-sensitive PKCα. Studies using a C-kinase activity reporter and a myristoylated alanine-rich protein kinase C substrate fused with green fluorescent protein (GFP) have also revealed that Cal-C at high concentrations activate PKC in living cells. Additionally, the PKC-activating effects of Cal-C were light-dependent. Finally, studies using Si-DMA, an indicator of singlet oxygen, showed that Cal-C at high concentrations generated singlet oxygen, causing structural changes in the ER and leakage of calcium into the cytosol, which triggered PKC activation. This study confirms the novel action of Cal-C, solely considered a PKC inhibitor. Cal-C acted as a PKC inhibitor at low concentrations and a PKC activator at high concentrations by generating singlet oxygen in a light-dependent manner, suggesting that Cal-C can be used in photodynamic therapy.

Epigenetic modifiers as inducer of bioactive secondary metabolites in fungi

Scientists are making efforts to search for new metabolites as they are essential lead molecules for the drug discovery, much required due to the evolution of multi drug resistance and new diseases. Moreover, higher production of known drugs is required because of the ever growing population. Microorganisms offer a vast collection of chemically distinct compounds that exhibit various biological functions. They play a crucial role in safeguarding crops, agriculture, and combating several infectious ailments and cancer. Research on fungi have grabbed a lot of attention after the discovery of penicillin, most of the compounds produced by fungi under normal cultivation conditions are discovered and now rarely new compounds are discovered. Treatment of fungi with the epigenetic modifiers has been becoming very popular since the last few years to boost the discovery of new molecules and enhance the production of already known molecules. Epigenetic literally means above genetics that actually does not alter the genome but alter its expression by altering the state of chromatin from heterochromatin to euchromatin. Chromatin in heterochromatin state usually doesn't express because it is closely packed by histones in this state. Epigenetic modifiers loosen the packing of chromatin by inhibiting DNA methylation and histone deacetylation and thus permit the expression of genes that usually remain dormant. This study delves into the possibility of utilizing epigenetic modifying agents to generate pharmacologically significant secondary metabolites from fungi.

Heat stress-induced NO enhanced perylenequinone biosynthesis of Shiraia sp. via calcium signaling pathway

Perylenequinones (PQs) are natural photosensitizing compounds used as photodynamic therapy, and heat stress (HS) is the main limiting factor of mycelial growth and secondary metabolism of fungi. This study aimed to unravel the impact of HS-induced Ca2+ and the calcium signaling pathway on PQ biosynthesis of Shiraia sp. Slf14(w). Meanwhile, the intricate interplay between HS-induced NO and Ca2+ and the calcium signaling pathway was investigated. The outcomes disclosed that Ca2+ and the calcium signaling pathway activated by HS could effectively enhance the production of PQs in Shiraia sp. Slf14(w). Further investigations elucidated the specific mechanism through which NO signaling molecules induced by HS act upon the Ca2+/CaM (calmodulin) signaling pathway, thus propelling PQ biosynthesis in Shiraia sp. Slf14(w). This was substantiated by decoding the downstream positioning of the CaM/CaN (calcineurin) pathway in relation to NO through comprehensive analyses encompassing transcript levels, enzyme assays, and the introduction of chemical agents. Concurrently, the engagement of Ca2+ and the calcium signaling pathway in heat shock signaling was also evidenced. The implications of our study underscore the pivotal role of HS-induced Ca2+ and the calcium signaling pathway, which not only participate in heat shock signal transduction but also play an instrumental role in promoting PQ biosynthesis. Consequently, our study not only enriches our comprehension of the mechanisms driving HS signaling transduction in fungi but also offers novel insights into the PQ synthesis paradigm within Shiraia sp. Slf14(w). KEY POINTS: • The calcium signaling pathway was proposed to participate in PQ biosynthesis under HS. • HS-induced NO was revealed to act upon the calcium signaling pathway for the first time.

Natural products as anthelmintics: safeguarding animal health

Covering literature to December 2022This review provides a comprehensive account of all natural products (500 compounds, including 17 semi-synthetic derivatives) described in the primary literature up to December 2022, reported to be capable of inhibiting the egg hatching, motility, larval development and/or the survival of helminths (i.e., nematodes, flukes and tapeworms). These parasitic worms infect and compromise the health and welfare, productivity and lives of commercial livestock (i.e., sheep, cattle, horses, pigs, poultry and fish), companion animals (i.e., dogs and cats) and other high value, endangered and/or exotic animals. Attention is given to chemical structures, as well as source organisms and anthelmintic properties, including the nature of bioassay target species, in vivo animal hosts, and measures of potency.

Biotechnological production and potential applications of hypocrellins

Hypocrellins (HYPs), a kind of natural perylenequinones (PQs) with an oxidized pentacyclic core, are important natural compounds initially extracted from the stromata of Hypocrella bambusae and Shiraia bambusicola. They have been widely concerned for their use as anti-microbial, anti-cancers, and anti-viral photodynamic therapy agents in recent years. Considering the restrictions of natural stromal resources, submerged fermentation with Shiraia spp. has been viewed as a promising alternative biotechnology for HYP production, and great efforts have been made to improve HYP production over the past decade. This article reviews recent publications about the mycelium fermentation production of HYPs, and their bioactivities and potential applications, and especially summarizes the progresses toward manipulation of fermentation conditions. Also, their chemical structure and analytic methods are outlined. Herein, it is worth mentioning that the gene arrangement in HYP gene cluster is revised; previous unknown genes in HYP and CTB gene clusters with correct function annotation are deciphered; the homologous sequences of HYP, CTB, and elc are systematically aligned, and especially the biosynthetic pathway of HYPs is full-scale proposed. KEY POINTS: • The mycelial fermentation process and metabolic regulation of hypocrellins are reviewed. • The bioactivities and potential applications of hypocrellins are summarized. • The biosynthesis pathway and regulatory mechanisms of hypocrellins are outlined.

Bamboo polysaccharides elicit hypocrellin A biosynthesis of a bambusicolous fungus Shiraia sp. S9

Hypocrellin A (HA), a fungal perylenequinone from bambusicolous Shiraia species, is a newly developed photosensitizer for photodynamic therapy in cancer and other infectious diseases. The lower yield of HA is an important bottleneck for its biomedical application. This study is the first report of the enhancement of HA production in mycelium culture of Shiraia sp. S9 by the polysaccharides from its host bamboo which serve as a strong elicitor. A purified bamboo polysaccharide (BPSE) with an average molecular weight of 34.2 kDa was found to be the most effective elicitor to enhance fungal HA production and characterized as a polysaccharide fraction mainly composed of arabinose and galactose (53.7: 36.9). When BPSE was added to the culture at 10 mg/L on day 3, the highest HA production of 422.8 mg/L was achieved on day 8, which was about 4.0-fold of the control. BPSE changed the gene expressions mainly responsible for central carbon metabolism and the cellular oxidative stress. The induced generation of H2O2 and nitric oxide was found to be involved in both the permeabilization of cell membrane and HA biosynthesis, leading to enhancements in both intra- and extracellular HA production. Our results indicated the roles of plant polysaccharides in host-fungal interactions and provided a new elicitation technique to improve fungal perylenequinone production in mycelium cultures.

Natural Perylenequinone Compounds as Potent Inhibitors of Schistosoma mansoni Glutathione S-Transferase

The existing treatment strategy for Schistosomiasis centers on praziquantel, a single drug, but its effectiveness is limited due to resistance and lack of preventive benefits. Thus, there is an urgent need for novel antischistosomal agents. Schistosoma glutathione S-transferase (GST) is an essential parasite enzyme, with a high potential for targeted drug discovery. In this study, we conducted a screening of compounds possessing antihelminth properties, focusing on their interaction with the Schistosoma mansoni glutathione S-transferase (SmGST) protein. We demonstrated the unique nature of SmGST in comparison to human GST. Evolutionary analysis indicated its close relationship with other parasitic worms, setting it apart from free-living worms such as C. elegans. Through an assessment of binding pockets and subsequent protein-ligand docking, we identified Scutiaquinone A and Scutiaquinone B, both naturally derived Perylenequinones, as robust binders to SmGST. These compounds have exhibited effectiveness against similar parasites and offer promising potential as antischistosomal agents.

Volatiles of Shiraia fruiting body-associated Pseudomonas putida No.24 stimulate fungal hypocrellin production

Hypocrellins are major bioactive perylenequinones from Shiraia fruiting bodies and have been developed as efficient photosensitizers for photodynamic therapy. Pseudomonas is the second dominant genus inside Shiraia fruiting bodies, but with less known actions on the host fungus. In this work, the effects of bacterial volatiles from the Shiraia-associated Pseudomonas on fungal hypocrellin production were investigated. Pseudomonas putida No.24 was the most active to promote significantly accumulation of Shiraia perylenequinones including hypocrellin A (HA), HC, elsinochrome A (EA) and EC. Headspace analysis of the emitted volatiles revealed dimethyl disulfide as one of active compounds to promote fungal hypocrellin production. The bacterial volatiles induced an apoptosis in Shiraia hyphal cell, which was associated with the generation of reactive oxygen species (ROS). ROS generation was proved to mediate the volatile-induced membrane permeability and up-regulation of gene expressions for hypocrellin biosynthesis. In the submerged volatile co-culture, the bacterial volatiles stimulated not only HA content in mycelia, but also HA secretion into the medium, leading to the enhanced HA production to 249.85 mg/L, about 2.07-fold over the control. This is the first report on the regulation of Pseudomonas volatiles on fungal perylenequinone production. These findings could be helpful to understand the roles of bacterial volatiles in fruiting bodies and also provide new elicitation method using bacterial volatiles to stimulate fungal secondary metabolite production.

Heat stress enhanced perylenequinones biosynthesis of Shiraia sp. Slf14(w) through nitric oxide formation

Perylenequinones (PQs) are a class of natural polyketides used as photodynamic therapeutics. Heat stress (HS) is an important environmental factor affecting secondary metabolism of fungi. This study investigated the effects of HS treatment on PQs biosynthesis of Shiraia sp. Slf14(w) and the underlying molecular mechanism. After the optimization of HS treatment conditions, the total PQs amount reached 577 ± 34.56 mg/L, which was 20.89-fold improvement over the control. Also, HS treatment stimulated the formation of intracellular nitric oxide (NO). Genome-wide analysis of Shiraia sp. Slf14(w) revealed iNOSL and cNOSL encoding inducible and constitutive NOS-like proteins (iNOSL and cNOSL), respectively. Cloned iNOSL in Escherichia coli BL21 showed higher nitric oxide synthase (NOS) activity than cNOSL, and the expression level of iNOSL under HS treatment was observably higher than that of cNOSL, suggesting that iNOSL is more responsible for NO production in the HS-treated strain Slf14(w) and may play an important role in regulating PQs biosynthesis. Moreover, the putative biosynthetic gene clusters for PQs and genes encoding iNOSL and nitrate reductase (NR) in the HS-treated strain Slf14(w) were obviously upregulated. PQs biosynthesis and efflux stimulated by HS treatment were significantly inhibited upon the addition of NO scavenger, NOS inhibitor, and NR inhibitor, indicating that HS-induced NO, as a signaling molecule, triggered promoted PQs biosynthesis and efflux. Our results provide an effective strategy for PQs production and contribute to the understanding of heat shock signal transduction studies of other fungi.Key points• PQs titer of Shiraia sp. Slf14(w) was significantly enhanced by HS treatment.• HS-induced NO was first reported to participate in PQs biosynthetic regulation.• Novel inducible and constitutive NOS-like proteins (iNOSL and cNOSL) were obtained and their NOS activities were determined.

Golgi-Targeting Anticancer Natural Products

The Golgi apparatus plays an important role in maintaining cell homeostasis by serving as a biosynthetic center for glycans, lipids and post-translationally modified proteins and as a sorting center for vesicular transport of proteins to specific destinations. Moreover, it provides a signaling hub that facilitates not only membrane trafficking processes but also cellular response pathways to various types of stresses. Altered signaling at the Golgi apparatus has emerged as a key regulator of tumor growth and survival. Among the small molecules that can specifically perturb or modulate Golgi proteins and organization, natural products with anticancer property have been identified as powerful chemical probes in deciphering Golgi-related pathways and, in particular, recently described Golgi stress response pathways. In this review, we highlight a set of Golgi-targeting natural products that enabled the characterization of the Golgi-mediated signaling events leading to cancer cell death and discuss the potential for selectively exploiting these pathways for the development of novel chemotherapeutic agents.

Effects of branched-chain amino acids on Shiraia perylenequinone production in mycelium cultures

BACKGROUND

Perylenequinones from Shiraia fruiting bodies are excellent photosensitizers and widely used for anti-cancer photodynamic therapy (PDT). The lower yield of Shiraia perylenequinones becomes a significant bottleneck for their medical application. Branched-chain amino acids (BCAAs) not only serve as important precursors for protein synthesis, but also are involved in signaling pathway in cell growth and development. However, there are few reports concerning their regulation of fungal secondary metabolism. In present study, the eliciting effects of BCAAs including L-isoleucine (L-Ile), L-leucine (L-Leu) and L-valine (L-Val) on Shiraia perylenequinone production were investigated.

RESULTS

Based on the analysis of the transcriptome and amino acid contents of Shiraia in the production medium, we revealed the involvement of BCAAs in perylenequinone biosynthesis. The fungal conidiation was promoted by L-Val treatment at 1.5 g/L, but inhibited by L-Leu. The spore germination was promoted by both. The production of fungal perylenequinones including hypocrellins A (HA), HC and elsinochromes A-C (EA-EC) was stimulated significantly by L-Val at 1.5 g/L, but sharply suppressed by L-Leu. After L-Val treatment (1.5 g/L) in Shiraia mycelium cultures, HA, one of the main bioactive perylenequinones reached highest production 237.92 mg/L, about 2.12-fold than that of the control. Simultaneously, we found that the expression levels of key genes involved in the central carbon metabolism and in the late steps for perylenequinone biosynthesis were up-regulated significantly by L-Val, but most of them were down-regulated by L-Leu.

CONCLUSIONS

Our transcriptome analysis demonstrated that BCAA metabolism was involved in Shiraia perylenequinone biosynthesis. Exogenous BCAAs exhibit contrasting effects on Shiraia growth and perylenequinones production. L-Val could promote perylenequinone biosynthesis via not only enhancing the central carbon metabolism for more precursors, but also eliciting perylenequinone biosynthetic gene expressions. This is the first report on the regulation of BCAAs on fungal perylenequinone production. These findings provided a basis for understanding physiological roles of BCAAs and a new avenue for increasing perylenequinone production in Shiraia mycelium cultures.

Naturally Occurring Partially Reduced Perylenequinones from Fungi

This Review provides a critical analysis of the literature covering the naturally occurring partially reduced perylenequinones (PQs) from fungi without carbon substituents (which can be named class A perylenequinones) and discusses their structures, stereochemistry, biosynthesis, and biological activities as appropriate. Perylenequinones are natural pigments with a perylene skeleton produced by certain fungi, aphids, some plants, and animal species. These compounds display several biological activities, e.g., antimicrobial, anti-HIV, photosensitizers, cytotoxic, and phytotoxic. It describes 36 fungal PQs and cites 81 references, covering from 1956 to August 2022.

Effects of Blue Light on Hypocrellin A Production in Shiraia Mycelium Cultures

Blue light is a crucial environmental cue for fungi. Hypocrellin A (HA) is a photoactive perylenequinone from Shiraia with strong antimicrobial and anticancer properties. In this study, effects of the illumination of blue light-emitting diode (LED) at 470 nm on Shiraia sp. S8 was investigated. Blue light at 50-200 lx and 4-6 h/day could enhance HA content in the mycelia, but suppress it at 300-400 lx or with longer exposure (8-24 h/day). The intermittent blue light (6 h/day) at 200 lx not only enhanced the fungal conidiation, but stimulated HA production without any growth retardation. The generation of fungal reactive oxygen species (ROS) was induced to up-regulate HA biosynthetic gene expressions. When the culture was maintained under the intermittent blue light for 8 days, HA production reached 242.76 mg/L, 2.27-fold of the dark control. On the other hand, both the degradation of HA and down-regulation of HA biosynthetic genes occurred under long exposure time (8-24 h/day), leading to the suppression of HA production. These results provide a basis for understanding the regulation of blue light on the biosynthesis of fungal photoactivated perylenequinones, and the application of a novel light elicitation to Shiraia mycelium cultures for enhanced HA production.

L-Arginine enhanced perylenequinone production in the endophytic fungus Shiraia sp. Slf14(w) via NO signaling pathway

Perylenequinones (PQ) are natural polyketides used as anti-microbial, -cancers, and -viral photodynamic therapy agents. Herein, the effects of L-arginine (Arg) on PQ biosynthesis of Shiraia sp. Slf14(w) and the underlying molecular mechanism were investigated. The total content of PQ reached 817.64 ± 72.53 mg/L under optimal conditions of Arg addition, indicating a 30.52-fold improvement over controls. Comparative transcriptome analysis demonstrated that Arg supplement promoted PQ precursors biosynthesis of Slf14(w) by upregulating the expression of critical genes associated with the glycolysis pathway, and acetyl-CoA and malonyl-CoA synthesis. By downregulating the expression of genes related to the glyoxylate cycle pathway and succinate dehydrogenase, more acetyl-CoA flow into the formation of PQ. Arg supplement upregulated the putative biosynthetic gene clusters for PQ and activated the transporter proteins (MFS and ABC) for exudation of PQ. Further studies showed that Arg increased the gene transcription levels of nitric oxide synthase (NOS) and nitrate reductase (NR), and activated NOS and NR, thus promoting the formation of nitric oxide (NO). A supplement of NO donor sodium nitroprusside (SNP) also confirmed that NO triggered promoted biosynthesis and efflux of PQ. PQ production stimulated by Arg or/and SNP can be significantly inhibited upon the addition of NO scavenger carboxy-PTIO, NOS inhibitor N_ω-nitro-L-arginine, or soluble guanylate cyclase inhibitor NS-2028. These results showed that Arg-derived NO, as a signaling molecule, is involved in the biosynthesis and regulation of PQ in Slf14(W) through the NO-cGMP-PKG signaling pathway. Our results provide a valuable strategy for large-scale PQ production and contribute to further understanding of NO signaling in the fungal metabolite biosynthesis. KEY POINTS: • PQ production of Shiraia sp. Slf14(w) was significantly improved by L-arginine addition. • Arginine-derived NO was firstly reported to be involved in the biosynthesis and regulation of PQ. • The NO-cGMP-PKG signaling pathway was proposed for the first time to participate in PQ biosynthesis.

Perylenequinone derivatives from the endolichenic fungus Phialocephala fortinii

Five undescribed perylenequinone derivatives (PQDs) phialocephalarins H - L (1 - 5), together with two known PQDs phialocephalarins A - B (6, 7) and one known spirobisnaphthalene palmarumycin P3 (8) were isolated from the endolichenic fungus Phialocephala fortinii. Their structures were elucidated on the basis of NMR and HRESIMS data as well as electronic circular dichroism (ECD) calculations. Compounds 1, 2, 4, and 6 - 8 were evaluated for cytotoxic activities against NCI-H460, NCI-H446, PC3, and EC109 cell lines. The results showed that compounds 1, 2, 6, and 8 showed cytotoxic activities against EC109 cells with IC₅₀ values ranging from 24.5 to 33.3 μM.

Photodynamic treatment of pathogens

The current viral pandemic has highlighted the compelling need for effective and versatile treatments, that can be quickly tuned to tackle new threats, and are robust against mutations. Development of such treatments is made even more urgent in view of the decreasing effectiveness of current antibiotics, that makes microbial infections the next emerging global threat. Photodynamic effect is one such method. It relies on physical processes proceeding from excited states of particular organic molecules, called photosensitizers, generated upon absorption of visible or near infrared light. The excited states of these molecules, tailored to undergo efficient intersystem crossing, interact with molecular oxygen and generate short lived reactive oxygen species (ROS), mostly singlet oxygen. These species are highly cytotoxic through non-specific oxidation reactions and constitute the basis of the treatment. In spite of the apparent simplicity of the principle, the method still has to face important challenges. For instance, the short lifetime of ROS means that the photosensitizer must reach the target within a few tens nanometers, which requires proper molecular engineering at the nanoscale level. Photoactive nanostructures thus engineered should ideally comprise a functionality that turns the system into a theranostic means, for instance, through introduction of fluorophores suitable for nanoscopy. We discuss the principles of the method and the current molecular strategies that have been and still are being explored in antimicrobial and antiviral photodynamic treatment.

Antimicrobial Effect of Phytochemicals from Edible Plants

Current strategies of combating bacterial infections are limited and involve the use of antibiotics and preservatives. Each of these agents has generally inadequate efficacy and a number of serious adverse effects. Thus, there is an urgent need for new antimicrobial drugs and food preservatives with higher efficacy and lower toxicity. Edible plants have been used in medicine since ancient times and are well known for their successful antimicrobial activity. Often photosensitizers are present in many edible plants; they could be a promising source for a new generation of drugs and food preservatives. The use of photodynamic therapy allows enhancement of antimicrobial properties in plant photosensitizers. The purpose of this review is to present the verified data on the antimicrobial activities of photodynamic phytochemicals in edible species of the world’s flora, including the various mechanisms of their actions.

Untapped Potential of Marine-Associated Cladosporium Species: An Overview on Secondary Metabolites, Biotechnological Relevance, and Biological Activities

The marine environment is an underexplored treasure that hosts huge biodiversity of microorganisms. Marine-derived fungi are a rich source of novel metabolites with unique structural features, bioactivities, and biotechnological applications. Marine-associated Cladosporium species have attracted considerable interest because of their ability to produce a wide array of metabolites, including alkaloids, macrolides, diketopiperazines, pyrones, tetralones, sterols, phenolics, terpenes, lactones, and tetramic acid derivatives that possess versatile bioactivities. Moreover, they produce diverse enzymes with biotechnological and industrial relevance. This review gives an overview on the Cladosporium species derived from marine habitats, including their metabolites and bioactivities, as well as the industrial and biotechnological potential of these species. In the current review, 286 compounds have been listed based on the reported data from 1998 until July 2021. Moreover, more than 175 references have been cited.

A bioinspired cercosporin/polymethylmethacrylate photocatalyst with high efficiency for decontamination of pharmaceuticals and pathogens

Pharmaceuticals have seriously contaminated aquatic environments and resulted in the formation of drug-tolerant bacteria owing to continuous release and accumulation. Therefore, the development of new methods to simultaneously decompose drugs and disinfect pathogens in an environmental-friendly manner with high efficiency is still in great demand. Bioinspired by the great photosensitivity of natural product cercosporin with the ability to efficiently generate reactive oxygen species (ROS) under natural sunlight and its antibacterial activity, here a novel cercosporin/polymethylmethacrylate (CP/PMMA) photocatalyst was rationally developed by incorporating and restricting cercosporin in a "green" macroporous resin PMMA, which greatly improved the ROS generation efficiency and displayed 97.2-100% photodegradation for broad-spectrum pharmaceuticals, including fluoroquinolones, trimethoprim and chloroquine phosphate, upon 15 W compact fluorescent lamp irradiation. More importantly, this decontamination efficiency was greatly improved, and the decontamination time was substantially shortened in a large-scale assay under natural sunlight. Furthermore, it could inactivate the pathogen Staphylococcus aureus. Overall, this work provides new insight into how a multifunctional photocatalyst could be designed using a natural product and macroporous resins for environmental remediation.

The signaling role of extracellular ATP in co-culture of Shiraia sp. S9 and Pseudomonas fulva SB1 for enhancing hypocrellin A production

Background

Adenosine 5′-triphosphate (ATP) plays both a central role as an intracellular energy source, and a crucial extracellular signaling role in diverse physiological processes of animals and plants. However, there are less reports concerning the signaling role of microbial extracellular ATP (eATP). Hypocrellins are effective anticancer photodynamic therapy (PDT) agents from bambusicolous Shiraia fungi. The co-culture of Shiraia sp. S9 and a bacterium Pseudomonas fulva SB1 isolated from Shiraia fruiting bodies was established for enhanced hypocrellin A (HA) production. The signaling roles of eATP to mediate hypocrellin biosynthesis were investigated in the co-culture.

Results

The co-culture induced release of eATP at 378 nM to the medium around 4 h. The eATP release was interdependent on cytosolic Ca²⁺ concentration and reactive oxygen species (ROS) production, respectively. The eATP production could be suppressed by the Ca²⁺ chelator EGTA or abolished by the channel blocker La³⁺, ROS scavenger vitamin C and NADPH oxidase inhibitor diphenyleneiodonium chloride (DPI). The bacterium-induced H₂O₂ production was strongly inhibited by reactive blue (RB), a specific inhibitor of membrane purinoceptors, but dependent on the induced Ca²⁺ influx in the co-culture. On the other hand, the application of exogenous ATP (exATP) at 10–300 µM to Shiraia cultures also promoted fungal conidiation and HA production, both of which were blocked effectively by the purinoceptor inhibitors pyridoxalphosphate-6-azophenyl-2′, 4′-disulfonic acid (PPADS) and RB, and ATP hydrolase apyrase. Both the induced expression of HA biosynthetic genes and HA accumulation were inhibited significantly under the blocking of the eATP or Ca²⁺ signaling, and the scavenge of ROS in the co-culture.

Conclusions

Our results indicate that eATP release is an early event during the intimate bacterial–fungal interaction and eATP plays a signaling role in the bacterial elicitation on fungal metabolites. Ca²⁺ and ROS are closely linked for activation of the induced ATP release and its signal transduction. This is the first report on eATP production in the fungal–bacterial co-culture and its involvement in the induced biosynthesis of fungal metabolites.

Graphic abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12934-021-01637-9.

Enhanced cercosporin production by co-culturing Cercospora sp. JNU001 with leaf-spot-disease-related endophytic bacteria

BACKGROUND

Owing to the excellent properties of photosensitization, cercosporin, one of naturally occurring perylenequinonoid pigments, has been widely used in photodynamic therapy, or as an antimicrobial agent and an organophotocatalyst. However, because of low efficiency of total chemical synthesis and low yield of current microbial fermentation, the limited production restricts its broad applications. Thus, the strategies to improve the production of cercosporin were highly desired. Besides traditional optimization methods, here we screened leaf-spot-disease-related endophytic bacteria to co-culture with our previous identified Cercospora sp. JNU001 to increase cercosporin production.

RESULTS

Bacillus velezensis B04 and Lysinibacillus sp. B15 isolated from leaves with leaf spot diseases were found to facilitate cercosporin secretion into the broth and then enhance the production of cercosporin. After 4 days of co-culture, Bacillus velezensis B04 allowed to increase the production of cercosporin from 128.2 mg/L to 984.4 mg/L, which was 7.68-fold of the previously reported one. Lysinibacillus sp. B15 could also enhance the production of cercosporin with a yield of 626.3 mg/L, which was 4.89-fold higher than the starting condition. More importantly, we found that bacteria B04 and B15 employed two different mechanisms to improve the production of cercosporin, in which B04 facilitated cercosporin secretion into the broth by loosening and damaging the hyphae surface of Cercospora sp. JNU001 while B15 could adsorb cercosporin to improve its secretion.

CONCLUSIONS

We here established a novel and effective co-culture method to improve the production of cercosporin by increasing its secretion ability from Cercospora sp. JNU001, allowing to develop more potential applications of cercosporin.

Nitric oxide donor sodium nitroprusside-induced transcriptional changes and hypocrellin biosynthesis of Shiraia sp. S9

Background

Nitric oxide (NO) is a ubiquitous signaling mediator in various physiological processes. However, there are less reports concerning the effects of NO on fungal secondary metabolites. Hypocrellins are effective anticancer photodynamic therapy (PDT) agents from fungal perylenequinone pigments of Shiraia. NO donor sodium nitroprusside (SNP) was used as a chemical elicitor to promote hypocrellin biosynthesis in Shiraia mycelium cultures.

Results

SNP application at 0.01–0.20 mM was found to stimulate significantly fungal production of perylenequinones including hypocrellin A (HA) and elsinochrome A (EA). SNP application could not only enhance HA content by 178.96% in mycelia, but also stimulate its efflux to the medium. After 4 days of SNP application at 0.02 mM, the highest total production (110.34 mg/L) of HA was achieved without any growth suppression. SNP released NO in mycelia and acted as a pro-oxidant, thereby up-regulating the gene expression and activity of reactive oxygen species (ROS) generating NADPH oxidase (NOX) and antioxidant enzymes, leading to the increased levels of superoxide anion (O₂⁻) and hydrogen peroxide (H₂O₂). Gene ontology (GO) analysis revealed that SNP treatment could up-regulate biosynthetic genes for hypocrellins and activate the transporter protein major facilitator superfamily (MFS) for the exudation. Moreover, SNP treatment increased the proportion of total unsaturated fatty acids in the hypha membranes and enhanced membrane permeability. Our results indicated both cellular biosynthesis of HA and its secretion could contribute to HA production induced by SNP.

Conclusions

The results of this study provide a valuable strategy for large-scale hypocrellin production and can facilitate further understanding and exploration of NO signaling in the biosynthesis of the important fungal metabolites.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12934-021-01581-8.

Fungal Pigments and Their Roles Associated with Human Health

Fungi can produce myriad secondary metabolites, including pigments. Some of these pigments play a positive role in human welfare while others are detrimental. This paper reviews the types and biosynthesis of fungal pigments, their relevance to human health, including their interactions with host immunity, and recent progresses in their structure-activity relationships. Fungal pigments are grouped into carotenoids, melanin, polyketides, and azaphilones, etc. These pigments are phylogenetically broadly distributed. While the biosynthetic pathways for some fungal pigments are known, the majority remain to be elucidated. Understanding the genes and metabolic pathways involved in fungal pigment synthesis is essential to genetically manipulate the production of both the types and quantities of specific pigments. A variety of fungal pigments have shown wide-spectrum biological activities, including promising pharmacophores/lead molecules to be developed into health-promoting drugs to treat cancers, cardiovascular disorders, infectious diseases, Alzheimer's diseases, and so on. In addition, the mechanistic elucidation of the interaction of fungal pigments with the host immune system provides valuable clues for fighting fungal infections. The great potential of fungal pigments have opened the avenues for academia and industries ranging from fundamental biology to pharmaceutical development, shedding light on our endeavors for disease prevention and treatment.

Modular engineering of Shiraia bambusicola for hypocrellin production through an efficient CRISPR system

Shiraia bambusicola exhibits an excellent capability to produce high-value pharmacological drugs, such as hypocrellin. However, less effective molecular tools hamper the processes to discover or exploit these metabolites. To address this issue, the more effective CRISPR/Cas9 system was constructed by optimizing the sgRNA transcription elements and disrupting the endogenous non-homologous end-joining pathway. These tactics prompted the gene-targeting frequency of 100% and simultaneously multiplex genome editing in S. bambusicola. This optimal CRISPR system encouraged us to rewire the entire hypocrellin flux and improve the yield by orchestrating the substrate pool supply, the central hypocrellin pathway, and the antioxidant system. Thus, 8632 mg/L hypocrellin was obtained, resulting in a 12-fold increase than that of the wild-type strain. This engineered S. bambusicola can still endure oxidative stresses from higher target metabolites and sustain an excellent biological activity. This study provides a whole conception to establish the more efficient genome-editing system. Higher conserved transcription elements for sgRNA expressions inspire us to adopt this system for gene modifications of other filamentous fungi. The rational and global biosystems outline will offer guidance to modulate metabolite productivity in other filamentous fungi.

Enhanced Production and Anticancer Properties of Photoactivated Perylenequinones

Hypocrellins and hypomycins are naturally occurring fungal perylenequinones with potential photodynamic activity against cancer and microbial diseases. This project pursued three lines of research. First, the production of perylenequinones was enhanced by investigating the effect of culture medium and light exposure on their biosynthesis. Solid-fermentation cultures on rice medium allowed for enhanced production of hypocrellins as compared to Cheerios or oatmeal medium. Alternatively, increased production of hypomycins, which are structurally related to the hypocrellins, was observed on oatmeal medium. In both cases, light exposure was an essential factor for the enhanced biosynthesis. In addition, this led to the discovery of two new perylenequinones, ent-shiraiachrome A (5) and hypomycin E (8), which were elucidated based on spectroscopic data. Finally, the photocytotoxic effects of both classes of compounds were evaluated against human skin melanoma, with EC50 values at nanomolar levels for hypocrellins and micromolar levels for hypomycins. In contrast, both classes of compounds showed reduced dark toxicity (EC50 values >100 μM), demonstrating promising phototherapeutic indices.

Transcriptome analysis on fructose as the sole carbon source enhancing perylenequinones production of endophytic fungus Shiraia sp. Slf14

Perylenequinones (PQ), a class of naturally occurring polypeptides, are widely used as a clinical drug for treating skin diseases and as a photodynamic therapy against cancers and viruses. In this study, the effects of different carbon sources on PQ biosynthesis by Shiraia sp. Slf14 were compared, and the underlying molecular mechanism of fructose as the sole carbon to enhance PQ production was investigated by transcriptome analysis. The results indicated that fructose enhanced PQ yield to 1753.64 mg/L, which was 1.73-fold higher than that obtained with glucose. Comparative transcriptome analysis demonstrated that most of the upregulated genes were related to transport systems, energy and central carbon metabolism in Shiraia sp. Slf14 cultured in fructose. The genes involved in glycolysis and pentose phosphate pathways, and encoding citrate synthase, ATP-citrate lyase, and acetyl-CoA carboxylase were substantially upregulated, resulting in increased overall acetyl-CoA and malonyl-CoA production. However, genes involved in gluconeogenesis, glyoxylate cycle pathway, and fatty acid synthesis were significantly downregulated, resulting in higher acetyl-CoA influx for PQ formation. In particular, the putative PQ biosynthetic cluster was upregulated in Shiraia sp. Slf14 cultured in fructose, leading to a significant increase in PQ production. The results of real-time qRT-PCR and related enzyme activities were also consistent with those of transcriptome analysis. These findings provide a remarkable insight into the underlying mechanism of PQ biosynthesis and pave the way for improvements in PQ production by Shiraia sp. Slf14.

Perylenequinonoid-catalyzed photoredox activation for the direct arylation of (het)arenes with sunlight

Naturally occurring perylenequinonoid pigments (PQPs) have attracted considerable attention owing to their excellent properties of photosensitization. They have been widely investigated as an aspect of photophysics and photobiology. However, their applications in photocatalysis are yet to be explored. We report here that sunlight along with 1 mol% cercosporin, which is one of the perylenequinonoid pigments, catalyzes the direct C-H bond arylation of (het)arenes by a photoredox process with good regioselectivity and broad functional group compatibility. Furthermore, a gram-scale reaction with great conversions of substrates was achieved even by a cercosporin-containing supernatant without organic solvent extraction and purification after liquid fermentation. Thus we set up a bridge between microbial fermentation and organic photocatalysis for chemical reactions in a sustainable, environmentally friendly manner.

Alternatone A, an Unusual Perylenequinone-Related Compound from a Soft-Coral-Derived Strain of the Fungus Alternaria alternata

A novel perylenequinone-related compound, alternatone A (1), with an unprecedented tricyclo[6.3.1.0^2,7] dodecane skeleton, together with three known perylenequinones, altertoxin I (2), stemphyperylenol (3), and alterperylenol (4), was isolated from the soft-coral-derived fungus Alternaria alternata L3111'. Their structures including absolute configurations were elucidated on the basis of comprehensive spectroscopic analysis, electronic circular dichroism calculations, and X-ray diffraction data. Compound 4 showed cytotoxicity against A-549, HCT-116, and HeLa cell lines with IC₅₀ values of 2.6, 2.4, and 3.1 μM, respectively. A possible biosynthetic pathway of 1 was proposed.

Bacteria Associated With Shiraia Fruiting Bodies Influence Fungal Production of Hypocrellin A

Hypocrellin A (HA) is a natural red perylenequinone pigment from Shiraia fruiting body, which was used clinically on various skin diseases and developed as a photodynamic therapy agent against cancers. The fruiting bodies may harbor a diverse but poorly understood microbial community. In this study, we characterized the bacterial community of Shiraia fruiting body using a combination of culture-based method and Illumina high-throughput sequencing, and tested the involvement of some companion bacteria in fungal HA production using the fungal-bacterial confrontation assay. Our results revealed that the bacterial community in the fruiting body was dominated by Bacillus and Pseudomonas. Some Pseudomonas isolates such as P. fulva, P. putida, and P. parafulva could stimulate fungal HA accumulation by Shiraia sp. S9. The bacterial treatment of P. fulva SB1 up-regulated the expression of polyketide synthase (PKS) for HA biosynthesis and transporter genes including ATP-binding cassette (ABC) and major facilitator superfamily transporter (MFS) for HA exudation. After the addition of live P. fulva SB1, the mycelium cultures of Shiraia sp. S9 presented a higher HA production (225.34 mg/L), about 3.25-fold over the mono-culture. On the other hand, B. cereus was capable of alleviating fungal self-toxicity from HA via down-regulation of HA biosynthetic genes or possible biodegradation on HA. To our knowledge, this is the first report on the diversified species of bacteria associated with Shiraia fruiting bodies and the regulation roles of the companion bacteria on fungal HA biosynthesis. Furthermore, the bacterial co-culture provided a good strategy for the enhanced HA production by Shiraia.

Trends and targets in antiviral phototherapy

Photodynamic therapy (PDT) is a well-established treatment option in the treatment of certain cancerous and pre-cancerous lesions. Though best-known for its application in tumor therapy, historically the photodynamic effect was first demonstrated against bacteria at the beginning of the 20^th century. Today, in light of spreading antibiotic resistance and the rise of new infections, this photodynamic inactivation (PDI) of microbes, such as bacteria, fungi, and viruses, is gaining considerable attention. This review focuses on the PDI of viruses as an alternative treatment in antiviral therapy, but also as a means of viral decontamination, covering mainly the literature of the last decade. The PDI of viruses shares the general action mechanism of photodynamic applications: the irradiation of a dye with light and the subsequent generation of reactive oxygen species (ROS) which are the effective phototoxic agents damaging virus targets by reacting with viral nucleic acids, lipids and proteins. Interestingly, a light-independent antiviral activity has also been found for some of these dyes. This review covers the compound classes employed in the PDI of viruses and their various areas of use. In the medical area, currently two fields stand out in which the PDI of viruses has found broader application: the purification of blood products and the treatment of human papilloma virus manifestations. However, the PDI of viruses has also found interest in such diverse areas as water and surface decontamination, and biosafety.

Inducing perylenequinone production from a bambusicolous fungus Shiraia sp. S9 through co-culture with a fruiting body-associated bacterium Pseudomonas fulva SB1

BACKGROUND

Fungal perylenequinonoid (PQ) pigments from Shiraia fruiting body have been well known as excellent photosensitizers for medical and agricultural uses. The fruiting bodies are colonized by a diverse bacterial community of unknown function. We screened the companion bacteria from the fruiting body of Shiraia sp. S9 and explored the bacterial elicitation on fungal PQ production.

RESULTS

A bacterium Pseudomonas fulva SB1 isolated from the fruiting body was found to stimulate the production of fungal PQs including hypocrellins A, C (HA and HC), and elsinochromes A-C (EA, EB and EC). After 2 days of co-cultures, Shiraia mycelium cultures presented the highest production of HA (325.87 mg/L), about 3.20-fold of that in axenic culture. The co-culture resulted in the induction of fungal conidiation and the formation of more compact fungal pellets. Furthermore, the bacterial treatment up-regulated the expression of polyketide synthase gene (PKS), and activated transporter genes of ATP-binding cassette (ABC) and major facilitator superfamily transporter (MFS) for PQ exudation.

CONCLUSIONS

We have established a bacterial co-culture with a host Shiraia fungus to induce PQ biosynthesis. Our results provide a basis for understanding bacterial-fungal interaction in fruiting bodies and a practical co-culture process to enhance PQ production for photodynamic therapy medicine.

The photoactivity of natural products - An overlooked potential of phytomedicines?

BACKGROUND

Photoactivity, though known for centuries, is only recently shifting back into focus as a treatment option against cancer and microbial infections. The external factor light is the ingenious key-component of this therapy: Since light activates the drug locally, a high level of selectivity is reached and side effects are avoided. The first reported photoactive medicines were plant extracts. Synthetic entities (so-called photosensitizers PSs), however, paved the route towards the clinical approval of the so-called photodynamic therapy (PDT), and thus natural PSs took a backseat in the past.

HYPOTHESIS

Many isolated bioactive phytochemicals hold a hidden photoactive potential, which is overlooked due to the reduced common awareness of photoactivity.

METHODS

A systematic review of reported natural PSs and their supposed medicinal application was conducted by employing PubMed, Scifinder, and Web of Science. The identified photoactive natural products were compiled including information about their natural sources, their photoyield, and their pharmacological application. Furthermore, the common chemical scaffolds of natural PS are shown to enable the reader to recognize potentially overlooked natural PSs.

RESULTS

The literature review revealed over 100 natural PS, excluding porphyrins. The PSs were classified according to their scaffold. Thereby it was shown that some PS-scaffolds were analyzed in a detailed way, while other classes were only scarcely investigated, which leaves space for future discoveries. In addition, the literature revealed that many PSs are phytoalexins, thus the selection of the starting material significantly matters in order to find new PSs.

CONCLUSION

Photoactive principles are ubiquitous and can be found in various plant extracts. With the increasing availability of light-irradiation setups for the identification of photoactive natural products, we anticipate the discovery of many new natural PSs in the near future. With the accumulation of chemically diverse PSs, PDT itself might finally reach its clinical breakthrough as a promising alternative treatment against multi-resistant microbes and cancer types.

Perylenequinonoid-Catalyzed [4 + 1] and [4 + 2] Annulations of Azoalkenes: Photocatalytic Access to 1,2,3-Thiadiazole/1,4,5,6-Tetrahydropyridazine Derivatives

Nitrogen-containing heterocycles are especially considered "privileged" structural scaffolds for the development of new drugs. However, traditional methods of organic synthesis are mainly based on thermal cycloaddition reaction; thus, the exploration of new strategies for the rapid assembly of N-heterocycles under mild conditions is highly desirable. Here, we developed a new method that visible light along with 1 mol % cercosporin, which is one of the perylenequinonoid pigments with excellent properties of photosensitization and can be easily produced by a new isolated endophytic fungus Cercospora sp. JNU001 strain with high yield through microbial fermentation, catalyzes the synthesis of 1,2,3-thiadiazoles and 1,4,5,6-tetrahydropyridazines by a photocatalytic process with good regioselectivity and broad functional-group compatibility under mild conditions. Thus, a bridge between microbial fermentation and organic photocatalysis for the construction of nitrogen-containing heterocycles was set up in a sustainable, environmentally friendly manner.

Perylenequinones from an endophytic Alternaria sp. of Pinus ponderosa

The differential solvent extraction and further purification of fractions of endophytic Alternaria sp. isolated from Pinus ponderosa led to the isolation of further two perylenequinone compounds as 3,6,6a,9,10-pentahydroxy-7,8-epoxy-4-oxo-4,5,6,6a,6b,7,8,9-octahydroperylene (1) and 3,6,6a,7,10-pentahydroxy-4,9-dioxo-4,5,6,6a,6b,7,8,9-octahydroperylene (2). Structure of compounds 1–2 was determined on the basis of detailed spectroscopic analysis, as well as by comparison with literature reports. The antimicrobial, antileismanial, antimalarial and cytotoxic activities of compound 1 and 2 were evaluated.

Enhanced production of perylenequinones in the endophytic fungus Shiraia sp. Slf14 by calcium/calmodulin signal transduction

Perylenequinones (PQ) that notably produce reactive oxygen species upon exposure to visible light are a class of photoactivated polyketide mycotoxins produced by fungal plant pathogens such as Shiraia sp. The involvement of Ca²⁺/calmodulin (CaM) signalling in PQ biosynthesis was investigated by submerged culturing of Shiraia sp. Slf14, a species that produces hypocrellins HA and HB and elsinochromes EA, EB, and EC. Our results showed that the total content of PQ reached 1894.66 ± 21.93 mg/L under optimal conditions of Ca²⁺ addition, which represents a 5.8-fold improvement over controls. The addition of pharmacological Ca²⁺ sensor inhibitors strongly inhibited PQ production, which indicates that Ca²⁺/CaM signalling regulates PQ biosynthesis. The expression levels of Ca²⁺ sensor and PQ biosynthetic genes were downregulated following addition of inhibitors but were upregulated upon addition of Ca²⁺. Inhibition was partially released by external Ca²⁺ supplementation. Fluo-3/AM experiments revealed that similar cytosolic Ca²⁺ variation occurred under these conditions. These results demonstrated that Ca²⁺ signalling via the CaM transduction pathway plays a pivotal role in PQ biosynthesis.

TD-DFT and structural investigation of natural photosensitive phenanthroperylene quinone derivatives

Structural modification of the phenanthroperylene quinone core affects the electronic structure of a series of natural product photosensitizers.

Characterization and phylogenetic analysis of the mitochondrial genome of Shiraia bambusicola reveals special features in the order of pleosporales

Shiraia bambusicola P. Henn. is a pathogenic fungus of bamboo, and its fruiting bodies are regarded as folk medicine. We determined and analyzed its complete mitochondrial DNA sequence (circular DNA molecule of 39,030 bp, G + C content of 25.19%). It contains the typical genes encoding proteins involved in electron transport and coupled oxidative phosphorylation (nad1-6 and nad4L, cob and cox1-3), one ATP synthase subunit (atp6), 4 hypothetical proteins, and two genes for large and small rRNAs (rnl and rns). There is a set of 32 tRNA genes comprising all 20 amino acids, and these genes are evenly distributed on the two strands. Phylogenetic analyses based on concatenated mitochondrial proteins indicated that S. bambusicola clustered with members of the order Pleosporales, which is in agreement with previous results. The gene arrangements of Dothideomycetes species contained three regions of gene orders partitioned in their mitochondrial genomes, including block 1 (nad6-atp6), block 2 (nad1-cox3) and block 3 (genes around rns). S. bambusicola displayed unique special features that differed from the other Pleosporales species, especially in the coding regions around rns (trnR-trnY). Moreover, a comparison of gene orders in mitochondrial genomes from Pezizomycotina revealed that although all encoded regions are located on the same strand in most Pezizomycotina mtDNAs, genes from Dothideomycetes species had different orientations, as well as diverse positions and colocalization of genes (such as cox3, cox1-cox2 and nad2-nad3); these distinctions were regarded as class-specific features. Interestingly, two incomplete copies of the atp6 gene were found on different strands of the mitogenomic DNA, a finding that has not been observed in the other analyzed fungal species. In our study, mitochondrial genomes from Dothideomycetes species were comprehensively analyzed for the first time, including many species that have not appeared in previous reports.

Anticancer and antifungal compounds from Aspergillus, Penicillium and other filamentous fungi

This review covers important anticancer and antifungal compounds reported from filamentous fungi and in particular from Aspergillus, Penicillium and Talaromyces. The taxonomy of these fungi is not trivial, so a focus of this review has been to report the correct identity of the producing organisms based on substantial previous in-house chemotaxonomic studies.

Mild aromatic palladium-catalyzed protodecarboxylation: kinetic assessment of the decarboxylative palladation and the protodepalladation steps

Mechanism studies of a mild palladium-catalyzed decarboxylation of aromatic carboxylic acids are described. In particular, reaction orders and activation parameters for the two stages of the transformation were determined. These studies guided development of a catalytic system capable of turnover. Further evidence reinforces that the second stage, protonation of the arylpalladium intermediate, is the rate-determining step of the reaction. The first step, decarboxylative palladation, is proposed to occur through an intramolecular electrophilic palladation pathway, which is supported by computational and mechanism studies. In contrast to the reverse reaction (C-H insertion), the data support an electrophilic aromatic substitution mechanism involving a stepwise intramolecular protonation sequence for the protodepalladation portion of the reaction.