Antifungal antibiotics

Bioactive Metabolites from Terrestrial and Marine Actinomycetes

Actinomycetes inhabit both terrestrial and marine ecosystems and are highly proficient in producing a wide range of natural products with diverse biological functions, including antitumor, immunosuppressive, antimicrobial, and antiviral activities. In this review, we delve into the life cycle, ecology, taxonomy, and classification of actinomycetes, as well as their varied bioactive metabolites recently discovered between 2015 and 2023. Additionally, we explore promising strategies to unveil and investigate new bioactive metabolites, encompassing genome mining, activation of silent genes through signal molecules, and co-cultivation approaches. By presenting this comprehensive and up-to-date review, we hope to offer a potential solution to uncover novel bioactive compounds with essential activities.

Antifungal activity screening of fractions from Annona cherimola Mill. leaf extract against Fusarium oxysporum

The antifungal effect of ethanolic extract fractions of Annona cherimola leaves against the mycelial growth of Fusarium oxysporum was studied. The ethanolic crude extract was solvent partitioned and the ethyl acetate phase was fractionated by column or preparative thin-layer chromatography. All fractions were developed on TLC and analyzed for acetogenins (ACG) with Kedde reagent. The antifungal effect assays were carried out in vitro by the diffusion method on PDA plates. The ethanolic extract of A. cherimola leaves was highly active against F. oxysporum growth; subfractions obtained from the antifungal screening had a significant effect (p < 0.05) on the F. oxysporum growth parameters. The screening showed that as the purification steps progressed, the inhibition of mycelial growth increased. Six bioactive ACG (Annomolon-B, 34-epi annomolon B, almunequin, cherimoline 1, cherimoline 2, and isocherimoline 1) were identified by LC-QTOF-MS/MS. These findings suggested that bioactive ACG from A. cherimola leaves could be an alternative resource of a promising botanical fungicide to control plant diseases caused by F. oxysporum.

Modahl C, Maenaka K, Aoki-Shioi N. Cysteine-Rich Secretory Proteins (CRISPs) From Venomous Snakes: An Overview of the Functional Diversity in A Large and Underappreciated Superfamily

The CAP protein superfamily (Cysteine-rich secretory proteins (CRISPs), Antigen 5 (Ag5), and Pathogenesis-related 1 (PR-1) proteins) is widely distributed, but for toxinologists, snake venom CRISPs are the most familiar members. Although CRISPs are found in the majority of venoms, very few of these proteins have been functionally characterized, but those that have been exhibit diverse activities. Snake venom CRISPs (svCRISPs) inhibit ion channels and the growth of new blood vessels (angiogenesis). They also increase vascular permeability and promote inflammatory responses (leukocyte and neutrophil infiltration). Interestingly, CRISPs in lamprey buccal gland secretions also manifest some of these activities, suggesting an evolutionarily conserved function. As we strive to better understand the functions that CRISPs serve in venoms, it is worth considering the broad range of CRISP physiological activities throughout the animal kingdom. In this review, we summarize those activities, known crystal structures and sequence alignments, and we discuss predicted functional sites. CRISPs may not be lethal or major components of venoms, but given their almost ubiquitous occurrence in venoms and the accelerated evolution of svCRISP genes, these venom proteins are likely to have functions worth investigating.

Two small, cysteine-rich and cationic antifungal proteins from Penicillium chrysogenum: A comparative study of PAF and PAFB

The filamentous fungus Penicillium chrysogenum Q176 secretes the antimicrobial proteins (AMPs) PAF and PAFB, which share a compact disulfide-bond mediated, β-fold structure rendering them highly stable. These two AMPs effectively inhibit the growth of human pathogenic fungi in micromolar concentrations and exhibit antiviral potential without causing cytotoxic effects on mammalian cells in vitro and in vivo.

The antifungal mechanism of action of both AMPs is closely linked to - but not solely dependent on - the lipid composition of the fungal cell membrane and requires a strictly regulated protein uptake into the cell, indicating that PAF and PAFB are not canonical membrane active proteins. Variations in their antifungal spectrum and their killing dynamics point towards a divergent mode of action related to their physicochemical properties and surface charge distribution.

In this review, we relate characteristic features of PAF and PAFB to the current knowledge about other AMPs of different sources. In addition, we present original data that have never been published before to substantiate our assumptions and provide evidences that help to explain and understand better the mechanistic function of PAF and PAFB. Finally, we underline the promising potential of PAF and PAFB as future antifungal therapeutics.

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Penicillium chrysogenum secretes the small, cysteine-rich proteins PAF and PAFB.

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Both exhibit antifungal activity, but with differences in their mode of action.

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Structure, membrane interaction and cellular uptake determine their function.

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PAF and PAFB are well tolerated by mammalian cells.

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They promise applicability in medicine, plant protection and food industry.

Antifungal Action of Antifungalmycin N2 Against Rhizoctonia solani by Disrupting Cell Membrane and Inhibiting Succinate Dehydrogenase

Antifungalmycin N2 (3-methyl-3,5-amino-4-vinyl-2-pyrone, C₆H₇O₂N) was a novel structural antifungal metabolite produced by Streptomyces sp. strain N2. Our previous study reported that the antagonistic interaction between antifungalmycin N2 and Rhizoctonia solani was accompanied by an oxidative stress in R. solani cell, indicating a probable damage occurred in the cell membranes and mitochondria. To verify this, the present study focused on investigating the effects of antifungalmycin N2 on the structure and function of cell membranes and mitochondria of R. solani. Morphological observations in transmission electron microscopy and fluorescence microscope showed that cell membranes of R. solani were damaged, and its cytoplasmic organelles were disorganized when treated with antifungalmycin N2. Meanwhile, the kinetics of membrane-related physiological and biochemical parameters, such as the increased malondialdehyde level, dropped ergosterol formation, and enhanced electrical conductivity in R. solani mycelia, further confirmed that antifungalmycin N2 would disrupt the cell membrane structure and function. More significantly, antifungalmycin N2 had a significantly inhibitory effect on the succinate dehydrogenase (SDH) activity of R. solani, and indicated that the mode and site of action of antifungalmycin N2 against R. solani might be similar to the existing succinate dehydrogenase inhibitors fungicides by binding in the ubiquinone-binding site. In conclusion, the above results demonstrated that the mode and site of action of antifungalmycin N2 targeted to cell membrane and SDH of R. solani, thus exerting the antifungal activity by damaging cell membrane structure and function, together with inhibiting the SDH activity.

Antagonistic activity of a novel antifungalmycin N2 from Streptomyces sp. N2 and its biocontrol efficacy against Rhizoctonia solani

Antifungalmycin N2 (3-methyl-3,5-amino-4-vinyl-2-pyrone, C6H7O2N) is a novel bioactive substance produced by Streptomyces sp. N2. In this present work, the antagonistic activity of antifungalmycin N2 and its biocontrol efficacy on Rhizoctonia solani were carried out to evaluate its potential as a biocontrol agent against fungal plant diseases. By using potato dextrose agar media for in vitro cultivation of phytopathogenic fungi, the results showed that antifungalmycin N2 not only displayed broad-spectrum antifungal activities against various plant pathogenic fungi, but also had a strong antagonism to the sclerotial germination of R. solani. In a detached leaf assay, it was found that antifungalmycin N2 could effectively protect the rice leaves form the infection of R. solani, resulting in a significantly reduced sheath blight severity on the surfaces of rice leaves. In the pot experiments, the results also revealed that significantly lower sheath blight infections occurred in the tissues of the treated rice plants, which further confirmed that antifungalmycin N2 had a favorable biocontrol efficacy on rice sheath blight. In conclusion, the above results indicated that the novel antifungalmycin N2 was one of promising biocontrol agents for plant disease control.

Actinomycete-Derived Polyketides as a Source of Antibiotics and Lead Structures for the Development of New Antimicrobial Drugs

Actinomycetes are remarkable producers of compounds essential for human and veterinary medicine as well as for agriculture. The genomes of those microorganisms possess several sets of genes (biosynthetic gene cluster (BGC)) encoding pathways for the production of the valuable secondary metabolites. A significant proportion of the identified BGCs in actinomycetes encode pathways for the biosynthesis of polyketide compounds, nonribosomal peptides, or hybrid products resulting from the combination of both polyketide synthases (PKSs) and nonribosomal peptide synthetases (NRPSs). The potency of these molecules, in terms of bioactivity, was recognized in the 1940s, and started the "Golden Age" of antimicrobial drug discovery. Since then, several valuable polyketide drugs, such as erythromycin A, tylosin, monensin A, rifamycin, tetracyclines, amphotericin B, and many others were isolated from actinomycetes. This review covers the most relevant actinomycetes-derived polyketide drugs with antimicrobial activity, including anti-fungal agents. We provide an overview of the source of the compounds, structure of the molecules, the biosynthetic principle, bioactivity and mechanisms of action, and the current stage of development. This review emphasizes the importance of actinomycetes-derived antimicrobial polyketides and should serve as a "lexicon", not only to scientists from the Natural Products field, but also to clinicians and others interested in this topic.

Discovery and evaluation on the antibacterial and cytotoxic activities of a novel antifungalmycin N2 produced from Streptomyces sp. strain N2

Antifungalmycin N2 (3-methyl-3,5-amino-4-vinyl-2-pyrone, C₆H₇O₂N) was a novel metabolite produced from Streptomyces sp. strain N2, and the present study aimed to evaluate its antibacterial and cytotoxic properties. By using Oxford cup method, the obtained results revealed that antifungalmycin N2 exhibited a significant antibacterial activity against the pathogenic bacteria such as Staphylococcus aureus, Escherichia coli, and Micrococcus kristinae, especially the Gram-positive S. aureus. Meanwhile, the MTT assay showed that antifungalmycin N2 could exert a marked inhibitory action on tumor cell lines, such as the cell lines of BEL-7402 (human hepatocellular carcinoma), Hela (human cervical carcinoma), HCT116 (human colon cancer), and SW620 (human colon cancer). And the IC₅₀ values antifungalmycin N2 against the above cell lines ranged from 11.23 to 15.37 μg/mL. In conclusion, the antibacterial and cytotoxic activities suggested that the novel antifungalmycin N2 was a promising active structure to be developed as new drug for treating infectious diseases and cancers.

Modeling and Statistical Optimization of Culture Conditions for Improvement of Antifungal Compounds Production by Streptomyces albidoflavus S19 Strain of Wastewater Origin

BACKGROUND

The actinomycetes strains isolated from unexplored ecosystems are a promising alternative for the biosynthesis of novel antimicrobial compounds. Depending on the interesting antifungal activity of the studied strain S19, the statistical method seems to be an effective tool for optimizing the production of anticandidal molecules.

INTRODUCTION

This study was conducted in order to optimize the culture parameters (medium nutrients concentrations and initial pH value) affecting the production of antifungal metabolites from S. albidoflavus strain S19 (obtained from wastewater collected in Bejaia region, Algeria) using Response Surface Metho-dology (RSM). The best conditions for anti-Candida albicans compounds biosynthesis were determined.

METHODS AND RESULTS

The antimicrobial producer strain S. albidoflavus S19 was identified on the basis of morphological, chemicals characters and physiological characteristics along with 16S rRNA gene se-quencing analysis.Response Surface Methodology by Central Composite Design (CCD) was employed to improve the anti-C. albicans agents production through the optimization of medium parameters. The highest antifungal ac-tivity was obtained by using a mixture of 2g l-1 starch, 4g l-1 yeast extract, 2g l-1 peptone at pH 11.

CONCLUSION

The strain S19 isolated from wastewater showed a significant anti-C. albicans activity and this study revealed the effectiveness of RSM and CCD for increasing bioactive compounds production, rising the diameter of inhibition zones from 13 to 34 mm.

The wood decay fungus Cerrena unicolor adjusts its metabolism to grow on various types of wood and light conditions

Cerrena unicolor is a wood-degrading basidiomycete with ecological and biotechnological importance. Comprehensive Biolog-based analysis was performed to assess the metabolic capabilities and sensitivity to chemicals of C. unicolor FCL139 growing in various sawdust substrates and light conditions. The metabolic preferences of the fungus towards utilization of specific substrates were shown to be correlated with the sawdust medium applied for fungus growth and the light conditions. The highest catabolic activity of C. unicolor was observed after fungus precultivation on birch and ash sawdust media. The fungus growing in the dark showed the highest metabolic activity which was indicated by capacity to utilize a broad spectrum of compounds and the decomposition of 74/95 of the carbon sources. In all the culture light conditions, p-hydroxyphenylacetic acid was the most readily metabolized compound. The greatest tolerance to chemicals was also observed during C. unicolor growth in darkness. The fungus was the most sensitive to nitrogen compounds and antibiotics, but more resistant to chelators. Comparative analysis of C. unicolor and selected wood-decay fungi from different taxonomic and ecological groups revealed average catabolic activity of the fungus. However, C. unicolor showed outstanding capabilities to catabolize salicin and arbutin. The obtained picture of C. unicolor metabolism showed that the fungus abilities to decompose woody plant material are influenced by various environmental factors.

Absorption of Codonopsis pilosula Saponins by Coexisting Polysaccharides Alleviates Gut Microbial Dysbiosis with Dextran Sulfate Sodium-Induced Colitis in Model Mice

Objectives

Inflammatory Bowel Disease (IBD) is an autoimmune disease, and the gut microbiota has become a new therapeutic target. Herbal medicine (HM) has shown good efficacy in the clinical treatment of IBD; however, the synergistic actions of the dominant chemicals in HM decoctions are unclear.

Methods

In this study, we explored whether the complicated interconnections between HM and the gut microbiota could allow crosstalk between HM ingredients. Saponins and polysaccharides, i.e., the dominant chemicals in the Codonopsis pilosula Nannf (CPN) decoction, were investigated in a dextran sulfate sodium- (DSS-) induced mouse model. Bacterial 16S rRNA sequencing analyzed the change of gut microbiota structure and diversity. Gas chromatography (GC) determined the content of short-chain fatty acids (SCFAs) in feces. ELISA detected the expression of proinflammatory and anti-inflammatory cytokines associated with TH17/Treg balance. UPLC-QTOF-MS technology combined with PKsolver software analyzed the absorption of the highest exposure for monomeric compounds of CPN saponins in serum. The results indicated that CPN polysaccharides showed prebiotic-like effects in mice with DSS-induced colitis by simultaneously stimulating the growth of three important probiotics, i.e., Bifidobacterium spp., Lactobacillus spp., and Akkermansia spp., and inhibiting the growth of pathogenic bacteria, including Desulfovibrio spp., Alistipes spp., and Helicobacter spp. Moreover, CPN polysaccharides improved intestinal metabolism, enhanced the production of short-chain fatty acids, upregulated the expression of anti-inflammatory cytokines and downregulated the secretion of proinflammatory cytokines correlated with Th17/Treg balance, promoted the absorption of certain CPN saponins in the serum, and stimulated recovery of the holistic gut microbiota.

Conclusion

CPN polysaccharides have the good prebiotic properties and shown good application prospects in the prevention and treatment of acute colitis. These findings provide insights into the specific bacteria responsible for active, inactive biotransformation of HM ingredients and those that are altered by HM administration.

Biosynthesis of Low Molecular Weight Antifungal Protein from Aspergillus giganteus in Batch Fermentation and In-Vitro Assay

　In present study, Taguchi's design of experiment L₉ orthogonal array was created using Qualitek-4 software with four most critical factors namely, K₂HPO₄, MgSO₄, CaCl₂ and culture pH. Production of a new intracellular antifungal protein in submerged fermentation was optimized with yield of 0.98±0.1 mg/gram dry cell weight mycelia from Aspergillus giganteus MTCC 8408. The average molecular mass of the purified protein was figured as 5.122 kDa using Electro Spray Ionization-Mass Spectrometry. Scanning electron microscopy was used to correlate the effect of selected factors on fungal cell morphology and its metabolite production. In vitro antifungal susceptibility assay was profiled against Aspergillus niger and minimum inhibitory concentrations were in the range 0.3±0.06 µg/ml. The stronger influencing factors on afp production and mycelial biomass were noted with CaCl₂ and K₂HPO₄ respectively. The validation experiments using optimized conditions confirmed an improvement in afp by 3.86 times with mycelial biomass by 1.52 times, compared to the basal medium. The present statistical optimization study revealed an opportunity to promote economical design at the industrial level for future scale up of effective antifungal agent against systemic aspergillosis as well as possible post harvest loss.

Therapeutic applications of bacterial pigments: a review of current status and future opportunities

Non-toxicity, biodegradability and non-carcinogenicity of the natural pigments, dyes and colorants make them an attractive source for human use. Bacterial pigments are colored metabolites secreted by bacteria under stress. The industrial uses of bacterial pigments have increased many folds because of several advantages over the synthetic pigments. Among natural resources, bacterial pigments are mostly preferred because of simple culturing and pigment extraction techniques, scaling up and being time economical. Generally, the bacterial pigments are safe for human use and therefore have a wide range of applications in pharmaceutical, textile, cosmetics and food industries. Therapeutic nature of the bacterial pigments is revealed because of their antimicrobial, anticancer, cytotoxic and remarkable antioxidant properties. Owing to the importance of bacterial pigments it was considered important to produce a comprehensive review of literature on the therapeutic and industrial potential of bacterial pigments. Extensive literature has been reviewed on the biomedical application of bacterial pigments while further opportunities and future challenges have been discussed.

Optimization and partial characterization of intracellular anticandidal protein from Aspergillus giganteus MTCC 8408 using taguchi DOE

A new intracellular antifungal protein (afp) production with average molecular weight 24.3 kDa and yield of 0.65 ± 0.1 mg/gram dry cell weight (gdcw) of mycelia in submerged fermentation of Aspergillus giganteus MTCC 8408 was optimized. Taguchi's DOE (design of experiment) L₂₇ orthogonal array (OA) was constructed using Qualitek-4 software with 8 most influensive factors namely, culture pH, temperature, slant age, inoculum volume, agitation and KH₂PO₄. Scanning electron microscopy (SEM) was used to correlate the effect of selected factors on fungal cell morphology and afp production. The crude protein purification was accomplished using pure ammonium sulfate fractionation followed by carboxymethyl cellulose (CMC) ion-exchange chromatography and sephadex G-100 gel filtration. The average molecular mass of the purified protein was figured by silver stained SDS (sodium dodecylsulphate)-PAGE (poly-acryl amide gel electrophoresis). In vitro antifungal susceptibility assay was profiled against Candida albicans NCIM 3471 and minimum inhibitory concentrations (MICs) were in the range 3 to 4 µg/ml. Characterization of protein was observed with FTIR (Fourier transform infrared spectroscopy) analysis. The optimal production condition for crude afp was obtained as follows: soluble starch: 20 g/l; Corn steep liquor (CSL, 2%) + proteose peptone (PP, 1%): 30 g/l; pH: 5.8; temperature: 25°C; slant age: 3 d; inoculum size: 5% (v/v); agitation: 180 rpm; KH₂PO₄: 0.1 g/l. The validation experiments using optimized conditions confirmed an improvement in afp production by 59.4% against the expected enhancement of afp production by 61.22%. The present statistical optimization study revealed an opportunity to promote economical design at the industrial level for future scale up of effective antifungal agent against opportunistic oral and vaginal infection.

Antimicrobial investigation of selected soil actinomycetes isolated from unexplored regions of Kashmir Himalayas, India

The aim of the present study was to isolate and evaluate the antimicrobial potential of soil actinomycetes of Kashmir Himalayas. The secondary metabolites of actinomycetes are the prominent source of antibiotics. A total of 121 morphologically different actinomycete strains were isolated and screened for antimicrobial activity against various human pathogens. The ethyl acetate extract of fermented broth an actinomycete strain, identified as Streptomyces pratensis exhibited significant antimicrobial activity against Staphylococcus aureus ATCC 29213 with MIC 0.25 μg/ml and Mycobacterium tuberculosis Strain H37Rv with MIC 0.062 μg/ml. The strain S. pratensis IIIM06 was grown on large scale and their broth was extracted with ethyl acetate. The extract was subjected to various chromatography techniques which led to the isolation of four compounds whose structures were established as actinomycin C1, actinomycin C2, actinomycin C3 and actiphenol on the basis of spectral data analysis. Actinomycin C1, C2 and C3 exhibited potent antimicrobial activity against S. aureus as well as M. tuberculosis. The isolated indigenous actinomycetes exhibited good antibacterial activity and the study reveals that IIIM06 is a promising strain and could be of great potential for industrial applications.

Multiple transporters are involved in natamycin efflux in Streptomyces chattanoogensis L10

Antibiotic-producing microorganisms have evolved several self-resistance mechanisms to prevent auto-toxicity. Overexpression of specific transporters to improve the efflux of toxic antibiotics has been found one of the most important and intrinsic resistance strategies used by many Streptomyces strains. In this work, two ATP-binding cassette (ABC) transporter-encoding genes located in the natamycin biosynthetic gene cluster, scnA and scnB, were identified as the primary exporter genes for natamycin efflux in Streptomyces chattanoogensis L10. Two other transporters located outside the cluster, a major facilitator superfamily transporter Mfs1 and an ABC transporter NepI/II were found to play a complementary role in natamycin efflux. ScnA/ScnB and Mfs1 also participate in exporting the immediate precursor of natamycin, 4,5-de-epoxynatamycin, which is more toxic to S. chattanoogensis L10 than natamycin. As the major complementary exporter for natamycin efflux, Mfs1 is up-regulated in response to intracellular accumulation of natamycin and 4,5-de-epoxynatamycin, suggesting a key role in the stress response for self-resistance. This article discusses a novel antibiotic-related efflux and response system in Streptomyces, as well as a self-resistance mechanism in antibiotic-producing strains.

Thailandins A and B, New Polyene Macrolactone Compounds Isolated from Actinokineospora bangkokensis Strain 44EHW(T), Possessing Antifungal Activity against Anthracnose Fungi and Pathogenic Yeasts

Two new polyene macrolactone antibiotics, thailandins A, 1, and B, 2, were isolated from the fermentation broth of rhizosphere soil-associated Actinokineospora bangkokensis strain 44EHW(T). The new compounds from this strain were purified using semipreparative HPLC and Sephadex LH-20 gel filtration while following an antifungal activity guided fractionation. Their structures were elucidated through spectroscopic techniques including UV, HR-ESI-MS, and NMR. These compounds demonstrated broad spectrum antifungal activity against fungi causing anthracnose disease (Colletotrichum gloeosporioides DoA d0762, Colletotrichum gloeosporiodes DoA c1060, and Colletotrichum capsici DoA c1511) as well as pathogenic yeasts (Candida albicans MT 2013/1, Candida parasilopsis DKMU 434, and Cryptococcus neoformans MT 2013/2) with minimum inhibitory concentrations ranging between 16 and 32 μg/mL. This is the first report of polyene antibiotics produced by Actinokineospora species as bioactive compounds against anthracnose fungi and pathogenic yeast strains.

Omics for Investigating Chitosan as an Antifungal and Gene Modulator

Chitosan is a biopolymer with a wide range of applications. The use of chitosan in clinical medicine to control infections by fungal pathogens such as Candida spp. is one of its most promising applications in view of the reduced number of antifungals available. Chitosan increases intracellular oxidative stress, then permeabilizes the plasma membrane of sensitive filamentous fungus Neurospora crassa and yeast. Transcriptomics reveals plasma membrane homeostasis and oxidative metabolism genes as key players in the response of fungi to chitosan. A lipase and a monosaccharide transporter, both inner plasma membrane proteins, and a glutathione transferase are main chitosan targets in N. crassa. Biocontrol fungi such as Pochonia chlamydosporia have a low content of polyunsaturated free fatty acids in their plasma membranes and are resistant to chitosan. Genome sequencing of P. chlamydosporia reveals a wide gene machinery to degrade and assimilate chitosan. Chitosan increases P. chlamydosporia sporulation and enhances parasitism of plant parasitic nematodes by the fungus. Omics studies allow understanding the mode of action of chitosan and help its development as an antifungal and gene modulator.

Streptomyces-derived actinomycin D inhibits biofilm formation by Staphylococcus aureus and its hemolytic activity

Staphylococcus aureus is a versatile human pathogen that produces diverse virulence factors, and its biofilm cells are difficult to eradicate due to their inherent ability to tolerate antibiotics. The anti-biofilm activities of the spent media of 252 diverse endophytic microorganisms were investigated using three S. aureus strains. An attempt was made to identify anti-biofilm compounds in active spent media and to assess their anti-hemolytic activities and hydrophobicities in order to investigate action mechanisms. Unlike other antibiotics, actinomycin D (0.5 μg ml(-1)) from Streptomyces parvulus significantly inhibited biofilm formation by all three S. aureus strains. Actinomycin D inhibited slime production in S. aureus and it inhibited hemolysis by S. aureus and caused S. aureus cells to become less hydrophobic, thus supporting its anti-biofilm effect. In addition, surface coatings containing actinomycin D prevented S. aureus biofilm formation on glass surfaces. Given these results, FDA-approved actinomycin D warrants further attention as a potential antivirulence agent against S. aureus infections.

The CAP protein superfamily: function in sterol export and fungal virulence

CAP superfamily proteins, also known as sperm-coating proteins, are found in all kingdoms of life and have been implicated in a variety of physiological contexts, including immune defense in plants and mammals, sperm maturation and fertilization, fungal virulence, and toxicity of insect and reptile venoms as well as prostate and brain cancer. CAP family members are mostly secreted glycoproteins that are highly stable in the extracellular fluid. All members of the superfamily share a common CAP domain of approximately 150 amino acids, which adopts a unique α-β-α sandwich fold. The conserved structure suggests that CAP proteins exert fundamentally similar functions. However, the molecular mode of action of this protein family has remained enigmatic. The budding yeast Saccharomyces cerevisiae has three CAP family members designated Pry (pathogen related in yeast), and recent evidence indicates that they act as sterol-binding and export proteins. Expression of the mammalian CAP protein CRISP2, which binds sterols in vitro, complements the sterol export defect of a yeast pry mutant, suggesting that sterol binding and export is conserved among different CAP family members. Collectively, these observations suggest that CAP family members constitute a novel class of secreted extracellular sterol-binding proteins. A ligand-binding activity of the CAP domain could explain many of the biological activities attributed to these proteins. For example, the strong induction of plant pathogenesis-related 1 protein upon exposure to pathogens may serve to inhibit pathogen proliferation by extracting sterols from the pathogen membrane. Similarly, the presence of these proteins in the venom of toxic insects and reptiles or in the secretome of pathogenic fungi might inflict damage by sequestering sterols or related small hydrophobic compounds from the host tissue.

Production of the antibiotic FR-008/candicidin in Streptomyces sp. FR-008 is co-regulated by two regulators, FscRI and FscRIV, from different transcription factor families

In Streptomyces sp. FR-008, the biosynthetic gene cluster of the polyene antibiotic FR-008, also known as candicidin, consists of 21 genes, including four regulatory genes, fscRI-fscRIV. Our bioinformatics analyses indicate that FscRI has an N-terminal PAS domain, whereas the other three regulators have N-terminal AAA domains and are members of the LAL (large ATP-binding regulators of the LuxR type) family. Deletion of fscRI abolished the production of FR-008, with production restored in the complemented strain, supporting a critical role for FscRI in FR-008 biosynthesis. Consistent with these findings, transcription of genes involved in the biosynthesis and efflux of FR-008 was greatly downregulated in a ΔfscRI mutant. Interestingly, the regulatory gene fscRIV was also downregulated in the ΔfscRI mutant. Production of FR-008 was reduced, but not abrogated, in an fscRIV deletion mutant, and although structural genes were downregulated in ΔfscRIV, the changes were much less dramatic than in ΔfscRI, suggesting a stronger regulatory role for FscRI. Remarkably, transcription of fscRI was also decreased in ΔfscRIV. Expression of fscRI restored antibiotic production in a ΔfscRIV mutant, but not vice versa. Putative binding sequences for FscRI were identified upstream of fscRIV and the three structural genes fscA, fscB and fscD, which encode large modular polyketide synthases. Our findings suggest that fscRI and fscRIV are interregulatory, whereas expression of fscRII and fscRIII appears to be independent of fscRI and fscRIV. This study demonstrates that the regulation of polyene antibiotic synthesis can involve mutually regulated transcriptional activators that belong to different families.

Sub-MICs of Carum copticum and Thymus vulgaris influence virulence factors and biofilm formation in Candida spp

BACKGROUND

Emergence of drug-resistant strains of Candida and inefficiency of conventional antifungal therapy has necessitated the search for alternative and new antifungal agents. Inhibition of virulence and biofilm are the potential drug targets. In this study, the oils of Carum copticum, Thymus vulgaris and their major active compound thymol as revealed by Gas chromatography and gas chromatography-mass spectrometry (GC-GC/MS) analysis were tested for their inhibitory activity against growth to determine sub-MIC values against 27 drug-resistant strains of Candida spp.

METHODS

Brothmacrodilution method was used for determination of MIC of test oils against Candida strains. The spectrophotometric methods were used for detection and inhibition assays for virulence factors in Candida spp. Light and electron microscopy was performed to observe morphological effects of oils on biofilms. GC-GC/MS were used to evaluate the major active compounds of test oils.

RESULTS

Virulence factors like proteinase and haemolysin were detected in 18 strains, both in solid and liquid media. A 70% of the test strains exhibited hydrophobicity and formed moderate to strong biofilms (OD280 0.5- > 1.0). Test oils exhibited MICs in the range of 45-360 μg.mL(-1) against the majority of test strains. All the oils at 0.25× and 0.5× MICs induced >70% reduction in the cell surface hydrophobicity, proteinase and haemolysin production. At 0.5× MIC, thymol and T. vulgaris were most inhibitory against biofilm formation. At sub-MICs electron microscopic studies revealed the deformity of complex structures of biofilms formed and cell membranes appeared to be the target site of these agents.

CONCLUSIONS

Therefore, our findings have highlighted the concentration dependent activity of oils of C. copticum and T. vulgaris against virulence factors and biofilms in proteinase and haemolysin producing drug-resistant strains of Candida spp. The above activities of test oils are supposed to be mainly contributed due to their major active compound thymol. Further mechanism involving anti-proteinase, anti-haemolysin and anti-biofilm activities of these oils and compounds are to be explored for possible exploitation in combating Candida infections.

Detection and quantification of a mycorrhization helper bacterium and a mycorrhizal fungus in plant-soil microcosms at different levels of complexity

BACKGROUND

Host plant roots, mycorrhizal mycelium and microbes are important and potentially interacting factors shaping the performance of mycorrhization helper bacteria (MHB). We investigated the impact of a soil microbial community on the interaction between the extraradical mycelium of the ectomycorrhizal fungus Piloderma croceum and the MHB Streptomyces sp. AcH 505 in both the presence and the absence of pedunculate oak microcuttings.

RESULTS

Specific primers were designed to target the internal transcribed spacer of the rDNA and an intergenic region between two protein encoding genes of P. croceum and the intergenic region between the gyrA and gyrB genes of AcH 505. These primers were used to perform real-time PCR with DNA extracted from soil samples. With a sensitivity of 10 genome copies and a linear range of 6 orders of magnitude, these real-time PCR assays enabled the quantification of purified DNA from P. croceum and AcH 505, respectively. In soil microcosms, the fungal PCR signal was not affected by AcH 505 in the absence of the host plant. However, the fungal signal became weaker in the presence of the plant. This decrease was only observed in microbial filtrate amended microcosms. In contrast, the PCR signal of AcH 505 increased in the presence of P. croceum. The increase was not significant in sterile microcosms that contained plant roots.

CONCLUSIONS

Real-time quantitative PCR assays provide a method for directly detecting and quantifying MHB and mycorrhizal fungi in plant microcosms. Our study indicates that the presence of microorganisms and plant roots can both affect the nature of MHB-fungus interactions, and that mycorrhizal fungi may enhance MHB growth.

Biosynthesis and pathway engineering of antifungal polyene macrolides in actinomycetes

Polyene macrolides are a large family of natural products typically produced by soil actinomycetes. Polyene macrolides are usually biosynthesized by modular and large type I polyketide synthases (PKSs), followed by several steps of sequential post-PKS modifications such as region-specific oxidations and glycosylations. Although known as powerful antibiotics containing potent antifungal activities (along with additional activities against parasites, enveloped viruses and prion diseases), their high toxicity toward mammalian cells and poor distribution in tissues have led to the continuous identification and structural modification of polyene macrolides to expand their general uses. Advances in in-depth investigations of the biosynthetic mechanism of polyene macrolides and the genetic manipulations of the polyene biosynthetic pathways provide great opportunities to generate new analogues. Recently, a novel class of polyene antibiotics was discovered (a disaccharide-containing NPP) that displays better pharmacological properties such as improved water-solubility and reduced hemolysis. In this review, we summarize the recent advances in the biosynthesis, pathway engineering, and regulation of polyene antibiotics in actinomycetes.

Purification and characterization of a novel antifungal protein secreted by Penicillium chrysogenum from an Arctic sediment

A fungal strain, Penicillium chrysogenum A096, was isolated from an Arctic sediment sample. Its culture supernatant inhibited mycelial growth of some plant pathogenic fungi. After saturation of P. chrysogenum A096 culture supernatant with ammonium sulfate and ion exchange chromatography, a novel antifungal protein (Pc-Arctin) was purified and identified by matrix assisted laser desorption ionization-time of flight-time of flight-mass spectrometry (MALDI-TOF-TOF-MS). The gene encoding for Pc-Arctin consisting of 195 nucleotides was cloned from P. chrysogenum A096 to confirm the mass spectrometry result. Pc-Arctin displays antifungal activity against Paecilomyces variotii, Alternaria longipes, and Trichoderma viride at minimum inhibitory concentrations (MIC) of 24, 48, and 192 ng/disc, respectively. Pc-Arctin was most sensitive to proteinase K and then to trypsin but insensitive to papain. Pc-Arctin possesses high thermostability and cannot be antagonized by common surfactants, except for sodium dodecyl sulfate (SDS). Divalent ions, such as Mn(2+), Mg(2+), and Zn(2+), inhibited the antifungal activity of Pc-Arctin. Hemagglutination assays showed that Pc-Arctin had no hemagglutinating or hemolytic activity against red blood cells (RBC) from rabbits, rats, and guinea pigs. Therefore, Pc-Arctin from Arctic P. chrysogenum may represent a novel antifungal protein with potential for application in controlling plant pathogenic fungal infection.

Two functional motifs define the interaction, internalization and toxicity of the cell-penetrating antifungal peptide PAF26 on fungal cells

The synthetic, cell penetrating hexapeptide PAF26 (RKKWFW) is antifungal at low micromolar concentrations and has been proposed as a model for cationic, cell-penetrating antifungal peptides. Its short amino acid sequence facilitates the analysis of its structure-activity relationships using the fungal models Neurospora crassa and Saccharomyces cerevisiae, and human and plant pathogens Aspergillus fumigatus and Penicillium digitatum, respectively. Previously, PAF26 at low fungicidal concentrations was shown to be endocytically internalized, accumulated in vacuoles and then actively transported into the cytoplasm where it exerts its antifungal activity. In the present study, two PAF26 derivatives, PAF95 (AAAWFW) and PAF96 (RKKAAA), were designed to characterize the roles of the N-terminal cationic and the C-terminal hydrophobic motifs in PAF26's mode-of-action. PAF95 and PAF96 exhibited substantially reduced antifungal activity against all the fungi analyzed. PAF96 localized to fungal cell envelopes and was not internalized by the fungi. In contrast, PAF95 was taken up into vacuoles of N. crassa, wherein it accumulated and was trapped without toxic effects. Also, the PAF26 resistant Δarg1 strain of S. cerevisiae exhibited increased PAF26 accumulation in vacuoles. Live-cell imaging of GFP-labelled nuclei in A. fumigatus showed that transport of PAF26 from the vacuole to the cytoplasm was followed by nuclear breakdown and dissolution. This work demonstrates that the amphipathic PAF26 possesses two distinct motifs that allow three stages in its antifungal action to be defined: (i) its interaction with the cell envelope; (ii) its internalization and transport to vacuoles mediated by the aromatic hydrophobic domain; and (iii) its transport from vacuoles to the cytoplasm. Significantly, cationic residues in PAF26 are important not only for the electrostatic attraction and interaction with the fungal cell but also for transport from the vacuole to the cytoplasm, which coincides with cell death. Peptide containment within vacuoles preserves fungal cells from peptide toxicity.

Enhancement of anti-candidal activity of endophytic fungus Phomopsis sp. ED2, isolated from Orthosiphon stamineus Benth, by incorporation of host plant extract in culture medium

This study examined the effect of host extract in the culture medium on anti-candidal activity of Phomopsis sp. ED2, previously isolated from the medicinal herb Orthosiphon stamineus Benth. Interestingly, upon addition of aqueous host extract to the culture medium, the ethyl acetate extract prepared from fermentative broth exhibited moderate anti-candidal activity in a disc diffusion assay. The minimal inhibitory concentration of this extract was 62.5 μg/ml and it only exhibited fungistatic activity against C. albicans. In the time-kill study, a 50% growth reduction of C. albicans was observed at 31.4 h for extract from the culture incorporating host extract. In the bioautography assay, only one single spot (Rf 0.59) developed from the extract exhibited anti-candidal activity. A spot with the a similar Rf was not detected for the crude extract from YES broth without host extract. This indicated that the terpenoid anti-candidal compound was only produced when the host extract was introduced into the medium. The study concluded that the incorporation of aqueous extract of the host plant into the culture medium significantly enhanced the anti-candidal activity of Phomopsis sp. ED2.

Identification and characterization of antifungal compounds using a Saccharomyces cerevisiae reporter bioassay

New antifungal drugs are urgently needed due to the currently limited selection, the emergence of drug resistance, and the toxicity of several commonly used drugs. To identify drug leads, we screened small molecules using a Saccharomyces cerevisiae reporter bioassay in which S. cerevisiae heterologously expresses Hik1, a group III hybrid histidine kinase (HHK) from Magnaporthe grisea. Group III HHKs are integral in fungal cell physiology, and highly conserved throughout this kingdom; they are absent in mammals, making them an attractive drug target. Our screen identified compounds 13 and 33, which showed robust activity against numerous fungal genera including Candida spp., Cryptococcus spp. and molds such as Aspergillus fumigatus and Rhizopus oryzae. Drug-resistant Candida albicans from patients were also highly susceptible to compounds 13 and 33. While the compounds do not act directly on HHKs, microarray analysis showed that compound 13 induced transcripts associated with oxidative stress, and compound 33, transcripts linked with heavy metal stress. Both compounds were highly active against C. albicans biofilm, in vitro and in vivo, and exerted synergy with fluconazole, which was inactive alone. Thus, we identified potent, broad-spectrum antifungal drug leads from a small molecule screen using a high-throughput, S. cerevisiae reporter bioassay.

Structural analysis and biosynthetic engineering of a solubility-improved and less-hemolytic nystatin-like polyene in Pseudonocardia autotrophica

Polyene antibiotics such as nystatin are a large family of very valuable antifungal polyketide compounds typically produced by soil actinomycetes. Previously, using a polyene cytochrome P450 hydroxylase-specific genome screening strategy, Pseudonocardia autotrophica KCTC9441 was determined to contain an approximately 125.7-kb region of contiguous DNA with a total of 23 open reading frames, which are involved in the biosynthesis and regulation of a structurally unique polyene natural product named NPP. Here, we report the complete structure of NPP, which contains an aglycone identical to nystatin and harbors a unique di-sugar moiety, mycosaminyl-(α1-4)-N-acetyl-glucosamine. A mutant generated by inactivation of a sole glycosyltransferase gene (nppDI) within the npp gene cluster can be complemented in trans either by nppDI-encoded protein or by its nystatin counterpart, NysDI, suggesting that the two sugars might be attached by two different glycosyltransferases. Compared with nystatin (which bears a single sugar moiety), the di-sugar containing NPP exhibits approximately 300-fold higher water solubility and 10-fold reduced hemolytic activity, while retaining about 50% antifungal activity against Candida albicans. These characteristics reveal NPP as a promising candidate for further development into a pharmacokinetically improved, less-cytotoxic polyene antifungal antibiotic.

Functional characterization of a synthetic hydrophilic antifungal peptide derived from the marine snail Cenchritis muricatus

Antimicrobial peptides have been found in mollusks and other sea animals. In this report, a crude extract of the marine snail Cenchritis muricatus was evaluated against human pathogens responsible for multiple deleterious effects and diseases. A peptide of 1485.26 Da was purified by reversed-phase HPLC and functionally characterized. This trypsinized peptide was sequenced by MS/MS technology, and a sequence (SRSELIVHQR), named Cm-p1 was recovered, chemically synthesized and functionally characterized. This peptide demonstrated the capacity to prevent the development of yeasts and filamentous fungi. Otherwise, Cm-p1 displayed no toxic effects against mammalian cells. Molecular modeling analyses showed that this peptide possible forms a single hydrophilic α-helix and the probable cationic residue involved in antifungal activity action is proposed. The data reported here demonstrate the importance of sea animals peptide discovery for biotechnological tools development that could be useful in solving human health and agribusiness problems.

Emergence of Candida spp. and exploration of natural bioactive molecules for anticandidal therapy--status quo

The opportunistic yeast pathogen Candida albicans and the emerging non-albicans Candida spp. cause life-threatening infections in immuno-compromised patients, leading to an increase in mortality rate. At present, the emergence of non-albicans Candida spp. causes serious infections that are difficult to treat the human populations worldwide. The available, synthetic antifungal drugs show high toxicity to host tissues causing adverse effects. Many metabolites of terrestrial and marine plants, microbes, algae, etc., contain a rich source of unexplored novel leads of different types, which are under use to treat various diseases. Such natural drugs are less expensive and have lower toxicity to host tissues. The patent search on identified and potential anticandidal-lead molecules, from various patent databases, has been described in this review. Furthermore, this article consolidates the trends in the development of anticandidal drug discovery worldwide. Most of the investigations on natural, bioactive molecules against candidiasis are in various phases of clinical trials, of which, two drugs Caspofungin acetate and Micafungin sodium were approved by the U.S. FDA. In conclusion, the exploration of drugs from natural resources serves as a better alternative source in anticandidal therapeutics, having great scope for drug discovery in the future.

Interaction of 5-(2, 4-dimethylbenzyl) pyrrolidin-2-one with selected antifungal drug target enzymes by in silico molecular docking studies

Currently the criteria used for selecting optimal new antifungal drug candidates include inhibitors of fungal cell wall biosynthesis, essential reaction and pathways. In silico approach resulting in the identification of essential reactions and pathways spreads across several parts of metabolism. The aim of the present study was to study the interaction of the isolated anti-Aspergillus compound, 5-(2, 4-dimethylbenzyl) pyrrolidin-2-one (DMBPO) from a novel Streptomyces VITSVK5 spp. with 6 selected antifungal drug target enzymes by in silico molecular docking approach. The compound DMBPO showed minimum binding energy (-6.66 kcal/mol) with 14 alpha-sterol demethylase (cyp51), (-5.65 kcal/mol) with Rubythrine, and (-4.43 kcal/mol) with β-1-3 Glucan binding protein. Two enzymes 14 alpha-sterol demethylase (cyp51) and β-1-3 Glucan were reported to be mostly responsible for drug resistance in Aspergillus species. The compound DMBPO interacted with several amino acid residues, of which leucine was found to be common among all the target enzymes for protein and hydrogen bond formation. Our results suggest that DMBPO could target Aspergillus fungal proteins to exhibit anti-Aspergillus activity in drug resistant strains.

Biological control of wood decay against fungal infection

Wood (timber) is an important raw material for various purposes, and having biological composition it is susceptible to deterioration by various agents. The history of wood protection by impregnation with synthetic chemicals is almost two hundred years old. However, the ever-increasing public concern and the new environmental regulations on the use of chemicals have created the need for the development and the use of alternative methods for wood protection. Biological wood protection by antagonistic microbes alone or in combination with (bio)chemicals, is one of the most promising ways for the environmentally sound wood protection. The most effective biocontrol antagonists belong to genera Trichoderma, Gliocladium, Bacillus, Pseudomonas and Streptomyces. They compete for an ecological niche by consuming available nutrients as well as by secreting a spectrum of biochemicals effective against various fungal pathogens. The biochemicals include cell wall-degrading enzymes, siderophores, chelating iron and a wide variety of volatile and non-volatile antibiotics. In this review, the nature and the function of the antagonistic microbes in wood protection are discussed.

In vitro efficacy of Myxococcus fulvus ANSM068 to biotransform aflatoxin B₁

Aflatoxin B₁ (AFB₁) is commonly found in cereals and animal feeds and causes a significant threat to the food industry and animal production. Several microbial isolates with high AFB₁ transformation ability have been identified in our previous studies. The aim of this research was to characterize one of those isolates, Myxococcus fulvus ANSM068, and to explore its biotransformation mechanism. The bacterial isolate of M. fulvus ANSM068, isolated from deer feces, was able to transform AFB₁ by 80.7% in liquid VY/2 medium after incubation at 30 °C for 72 h. The supernatant of the bacterial culture was more effective in transforming AFB₁ as compared to the cells alone and the cell extract. The transformation activity was significantly reduced and eradicated after the culture supernatant was treated with proteinase K, proteinase K plus SDS and heating. Culture conditions, including nitrogen source, initial pH and incubation temperature were evaluated for an optimal AFB₁ transformation. Liquid chromatography mass spectrometry (LCMS) analyses showed that AFB₁ was transformed to a structurally different compound. Infrared analysis (IR) indicated that the lactone ring on the AFB₁ molecule was modified by the culture supernatant. Chromatographies on DEAE-Ion exchange and Sephadex-Molecular sieve and SDS-PAGE electrophoresis were used to determine active components from the culture supernatant, indicating that enzyme(s) were responsible for the AFB₁ biotransformation. This is the first report on AFB₁ transformation by a strain of myxobacteria through enzymatic reaction(s).

Screening for antifungal peptides and their modes of action in Aspergillus nidulans

Many short cationic peptides have been identified as potent antimicrobial agents, but their modes of action are not well understood. Peptide synthesis on cellulose membranes has resulted in the generation of peptide libraries, while high-throughput assays have been developed to test their antibacterial activities. In this paper a microtiter plate-based screening method for fungi has been developed and used to test nine antibacterial peptides against the model fungus Aspergillus nidulans. Microscopical studies using sublethal peptide concentrations caused defects in polarized growth, including increased branch formation and depolarized hyphae. We characterized the mode of action for one of our target peptides, Sub5 (12 amino acids), which has already been shown to possess pharmacological potential as an antibacterial agent and is able to interact with ATP and ATP-dependent enzymes. The MIC for A. nidulans is 2 μg/ml, which is in the same range as the MICs reported for bacteria. Fluorescein isothiocyanate (FITC)-labeled Sub5 targeted the cytoplasmic membrane, particularly hyphal tips, and entered the cytoplasm after prolonged exposure, independent of endocytosis. Interestingly, Sub5 peptide treatment disturbed sterol-rich membrane domains, important for tip growth, at hyphal tips. A very similar peptide, FITC-P7, also accumulated on the cell membrane but did not have antibacterial or antifungal activity, suggesting that the cytoplasmic membrane is a first target for the Sub5 peptide; however, the antifungal activity seems to be correlated with the ability to enter the cytoplasm, where the peptides might act on other targets.

Characterization of theEscherichia coliAntifungal Protein PPEBL21

An antifungal protein isolated from Escherichia coli BL21 (PPEBL21) and predicted to be alcohol dehydrogenase (ADH) was subjected to biological characterization. The PPEBL21, indeed, demonstrated propionaldehyde-specific ADH activity. The Km and Vmax of PPEBL21 were found to be 644.8 μM and 1.2 U/mg, respectively. In-gel activity assay also showed that PPEBL21 was a propionaldehyde-specific ADH. The pI of PPEBL21 was observed to be 7.8. PPEBL21 was found to be stable up to a temperature of 40°C with optimum activity at pH 7.5. The decrease in pH decreased the activity of PPEBL21. These results suggested that PPEBL21 having alcohol dehydrogenase activity and stability at significantly high temperature might be an important lead antifungal molecule. Experiments were performed to identify the possible target of PPEBL21 in the pathogen A. fumigatus. Results revealed that PPEBL21 inhibited completely the expression of a 16 kDa protein in A. fumigatus. The 16 kDa protein of A. fumigatus targeted by PPEBL21 was identified as a hypothetical protein by peptide mass fingerprinting. It is thus hypothesized that a 16 kDa factor is essentially required by A. fumigatus for survival and its impaired synthesis due to treatment with PPEBL21 may lead to the death of pathogen.