Antimicrobial and morphogenic effects of emodin produced by Aspergillus awamori WAIR120

Antimicrobial Action Mechanisms of Natural Compounds Isolated from Endophytic Microorganisms

Infectious diseases are a significant challenge to global healthcare, especially in the face of increasing antibiotic resistance. This urgent issue requires the continuous exploration and development of new antimicrobial drugs. In this regard, the secondary metabolites derived from endophytic microorganisms stand out as promising sources for finding antimicrobials. Endophytic microorganisms, residing within the internal tissues of plants, have demonstrated the capacity to produce diverse bioactive compounds with substantial pharmacological potential. Therefore, numerous new antimicrobial compounds have been isolated from endophytes, particularly from endophytic fungi and actinomycetes. However, only a limited number of these compounds have been subjected to comprehensive studies regarding their mechanisms of action against bacterial cells. Furthermore, the investigation of their effects on antibiotic-resistant bacteria and the identification of biosynthetic gene clusters responsible for synthesizing these secondary metabolites have been conducted for only a subset of these promising compounds. Through a comprehensive analysis of current research findings, this review describes the mechanisms of action of antimicrobial drugs and secondary metabolites isolated from endophytes, antibacterial activities of the natural compounds derived from endophytes against antibiotic-resistant bacteria, and biosynthetic gene clusters of endophytic fungi responsible for the synthesis of bioactive secondary metabolites.

The role of chitosan in enhancing the solubility and antibacterial activity of emodin against drug-resistant bacteria

Similar to most anthraquinone compounds, the pharmacological properties of emodin are limited because of its low water solubility. In this study, the formulation of chitosan and emodin (EMD/CS) was prepared by a bottom-up method with precipitation and sonication steps in order to enhance the solubility of emodin. Thanks to the interactions of oxygen-and nitrogen-containing groups in chitosan with emodin molecules, the solubility of emodin in the formulation was remarkably increased to 0.5 mg/mL. The EMD/CS particles were well dispersed and distributed in a range of sub-micrometer with an average particle size of 342 nm. The EMD/CS formulation exhibited synergic antibacterial activity of emodin and chitosan, against drug-resistant bacterial strains, namely Methicillin-resistant Staphylococcus aureus (MRSA) and Escherichia coli O157:H7 (E. coli O157:H7). When the compositions of emodin and chitosan increased, the antibacterial effectiveness of the EMD/CS formulation increased. The EMD/CS formulation with compositions of 0.5 mg/mL of emodin and 9.0 mg/mL of chitosan could significantly inhibit the proliferation of E. coli O157:H7. Meanwhile, the EMD/CS formulation with a lower concentration of emodin (0.4 mg/mL) and chitosan (7.2 mg/mL) could cause an extermination effect on MRSA. The enhanced solubility of EMD/CS formulation suggests that this formulation can be a potential candidate for the treatment of infectious diseases caused by drug-resistant bacterial pathogens.

Microbial Natural Products with Wound-Healing Properties

Wound healing continues to pose a challenge in clinical settings. Moreover, wound management must be performed properly and efficiently. Acute wound healing involves multiple cell divisions, a new extracellular matrix, and the process of formation, such as growth factors and cytokines, which are released at the site of the wound to regulate the process. Any changes that disrupt the healing process could cause tissue damage and prolong the healing process. Various factors, such as microbial infection, oxidation, and inflammation, can delay wound healing. In order to counter these problems, utilizing natural products with wound-healing effects has been reported to promote this process. Several natural products have been associated with wound healing, most of which are from medicinal plants. However, secondary microbial metabolites have not been extensively studied for their wound-healing properties. Further, investigations on the wound-healing control of natural microbial products are required due to a lack of studies. This review discussed the in vivo and in vitro research on the wound healing activities of natural microbial products, which may assist in the development of better wound treatments in the future.

Aptamer decorated emodin nanoparticles-assisted delivery of dermcidin-derived peptide DCD-1L: Photoactive bio-theragnostic agent for Enterococcus faecalis biofilm destruction

BACKGROUND

Despite the high success rate of root canal treatment, failures are observed in a broad range of cases. Therefore, the need for novel approaches with the development of new generations of antimicrobial agents and intracellular drug delivery systems as adjunctive therapy is undeniable. In this study, we investigated the antimicrobial effects of antimicrobial photodynamic therapy (aPDT) using dermcidin‑derived peptide DCD‑1L loaded onto aptamer-functionalized emodin nanoparticles (Apt@EmoNp-DCD-1L) against Enterococcus faecalis as one of the most common bacteria involved in recurrent root canal treatment failures.

MATERIALS AND METHODS

Following preparation of EmoNp-DCD-1L, the binding of selected labeled Apt to EmoNp-DCD-1L was performed, followed by the specificity of Apt@EmoNp-DCD-1L to E. faecalis was determined. The antimicrobial potential of aPDT was then assessed after the determination of the minimum inhibitory concentration (MIC) of Apt@EmoNp-DCD-1L. The molecular docking analysis was conducted to evaluate the potential binding modes of EmoNp to the proteins involved in E. faecalis pathogenesis. Eventually, the anti-virulence capacity of Apt@EmoNp-DCD-1L-mediated aPDT was investigated via quantitative real-time PCR (qRT-PCR) assay following measurement of intracellular reactive oxygen species (ROS) generation.

RESULTS

The binding specificity of Apt@EmoNp-DCD-1L to E. faecalis was confirmed by flow cytometry. The results showed that the cell viability of E. faecalis exposed to aPDT groups employing the sub-MIC doses of Apt@EmoNp-DCD-1L (7.8 and 15.6 µM) was significantly reduced compared to the control group (P < 0.05). Also, Apt@EmoNp-DCD-1L in combination with a blue laser light was capable of enhancing the anti-biofilm activity of aPDT against E. faecalis biofilm. Data obtained from the qRT-PCR analysis showed significant downregulation in the expression level of genes involved in bacterial biofilm formation after exposure to aPDT (P < 0.05).

CONCLUSIONS

This in vitro study highlights that aPDT with the minimum concentration of Apt@EmoNp-DCD-1L can be considered as a targeted bio-theragnostic agent for the detection and elimination of E. faecalis in the dispersed and biofilm states.

Theranostic nanoplatforms of emodin-chitosan with blue laser light on enhancing the anti-biofilm activity of photodynamic therapy against Streptococcus mutans biofilms on the enamel surface

Background

Combining photosensitizer and light irradiation, named antimicrobial photodynamic therapy (aPDT) is an adjuvant therapy for eliminating microbial biofilms. This ex vivo study evaluates the effect of anti-biofilm activity of aPDT based on emodin-chitosan nanoparticles (Emo-CS-NPs) plus blue laser light against Streptococcus mutans biofilm on the enamel surface.

Materials

After determination of the fractional inhibitory concentration index of Emo and CS by checkerboard array assay, Emo-CS-NPs were synthesized and characterized. Following treatment of pre-formed S. mutans biofilms on the enamel slabs, cellular uptake of Emo-CS-NPs and intracellular reactive oxygen species (ROS) production were determined. The anti-biofilm and anti-metabolic activities of aPDT were investigated. Eventually, lactic acid production capacity, concentrations of S. mutans extracellular DNA (eDNA) levels, and expression of the gene involved in the biofilm formation (gtfB) were evaluated.

Results

The maximum uptake of Emo-CS-NPs occurs in an incubation time of 5 min. When irradiated, Emo-CS-NPs were photoactivated, generating ROS, and led to a decrease in the cell viability and metabolic activity of S. mutans significantly (P < 0.05). S. mutans eDNA and lactic acid production outcomes indicated that Emo-CS-NPs-mediated aPDT led to a significant reduction of eDNA levels (48%) and lactic acid production (72.4%) compared to the control group (P < 0.05). In addition, gtfB mRNA expression in S. mutans was downregulated (7.8-fold) after aPDT in comparison with the control group (P < 0.05).

Conclusions

Our data support that, aPDT using Emo-CS-NPs revealed the highest cellular uptake and ROS generation. Emo-CS-NPs based aPDT could inhibit significantly biofilm formation and reduce effectively virulence potency of S. mutans; thus, it could be an adjuvant therapy against dental caries.

Two Polyketides Produced by Endophytic Penicillium citrinum DBR-9 From Medicinal Plant Stephania kwangsiensis and Their Antifungal Activity Against Plant Pathogenic Fungi

Endophytic fungi, especially those found in medicinal plants, are widely studied as producers of secondary metabolites of biotechnological interest. In this study, on the basis of an activity-directed isolation method and spectroscopic analysis, two active polyketides, citrinin (1) and emodin (2), were isolated and identified from the fermentation of the endophytic fungus Penicillium citrinum DBR-9. This fungus was isolated from the root tubers of the traditional Chinese medicinal plant Stephania kwangsiensis. In vitro antifungal assay showed that the two polyketides displayed significant inhibition on hypha growth of tested plant pathogenic fungi with IC50 values ranging from 3.1 to 123.1 μg/mL and 3.0 to 141.0 μg/mL, respectively. In addition, the mechanism of the effects of emodin (2) on the pathogen revealed it could affect the colony morphology, destroy cell membrane integrity, and influence the protein synthesis of the tested fungal cell. This work is the first report of two polyketides-producing endophytic P. citrinum DBR-9 from the medicinal plant S. kwangsiensis. Our results present new opportunities to deeply understand the potential of these two polyketides as natural antifungal agents to control phytopathogens in agriculture.

Metabolic engineering of Saccharomyces cerevisiae for efficient production of endocrocin and emodin

The anthraquinones endocrocin and emodin are synthesized by a special class of type I NR-PKSs and a discrete MβL-TE. In this work, we first reconstituted a biosynthetic pathway of endocrocin and emodin in S. cerevisiae by combining enzymes from different sources. We functionally characterized a TE-less NR-PKS (SlACAS) and a MβL-TE (SlTE) from S. lycopersici as well as four orthologous MβL-TEs. SlACAS was coexpressed with different MβL-TEs in S. cerevisiae. SlACAS generated the highest amount of endocrocin when coupled with HyTE, the yield was 115.6% higher than that with the native SlTE. To accumulate more emodin, seven decarboxylases with high homology to HyDC were identified and introduced into the biosynthetic pathway. Among these orthologs, AfDC exhibited the highest catalytic activity and the conversion rate reached 98.6%. A double-point mutant acetyl-CoA carboxylase, ACC1^{S659A, S1157A}, was further introduced to increase the production of malonyl-CoA as a precursor of these anthraquinones. The production of endocrocin (233.6 ± 20.3 mg/L) and emodin (253.2 ± 21.7 mg/L) then dramatically increased. We also optimized the carbon source in the medium and conducted fed-batch fermentation with the engineered strains. The titers of endocrocin and emodin obtained were 661.2 ± 50.5 mg/L and 528.4 ± 62.7 mg/L, respectively, which are higher than previously reported. In this work, by screening a small library of orthologous biosynthetic bricks, an efficient biosynthetic pathway of endocrocin and emodin was first created in S. cerevisiae. This study provides a novel metabolic engineering approach for optimization of the production of desired molecules.

Overview on antibacterial metabolites from terrestrial Aspergillus spp

Medicines developed from natural sources are a frequent target for the research and discovery of antimicrobial compounds. Discovering of penicillin in 1928 was a motive to explore of nature as a source of new antimicrobial agents. Fungi produce a diverse range of bioactive metabolites, making them rich source of different types of medicines. The purpose of this paper was to review studies on antibacterials from terrestrial Aspergillus published exclusively during 1942-2018, with emphasis on their antibacterial activities, structures, and mechanisms of action if present. According to the results from different studies in the world, large number of compounds and extracts showed different activities against different bacterial species, including Gram-positive and Gram-negative bacteria. The most prominent result was that of the compound CJ-17,665, isolated from A. ochraceus, showing good activity against multi-drug resistant Staphylococcus aureus, which is well-recognised to be one of the most important current public health problem. These findings may motivate scientists to undertake a project that may result in the development of novel antibacterial drugs from terrestrial-derived Aspergillus spp., although further toxicity assays (in vivo) must be performed before their application.