Antifungal peptides produced by actinomycetes and their biological activities against plant diseases

Synthesis and antifungal activity of novel amide derivatives from quinic acid against the sweet potato pathogen Ceratocystis fimbriata

BACKGROUND

Ceratocystis fimbriata is a fungal pathogen that infects sweet potato roots, producing enormous economic losses. Cyclic polyhydroxy compound quinic acid is a common metabolite synthesized in plant tissues, including sweet potato tubers, showing weak antifungal properties. Although several O-acylated quinic acid derivatives have been synthesized and found in nature and their antifungal properties have been explored, derivatives based on modification of the carboxylic acid have never been evaluated.

RESULTS

In this study, amide derivatives were synthesized via linkage of amines with the carboxylic acid moiety of quinic acid. Derivatives with high dipolar moments and a low number of rotatable bonds showed greater antifungal activities toward C. fimbriata in vitro than quinic and chlorogenic acids. Derivative 5b, which was synthesized by coupling p-aminobenzoic acid (pABA) with quinic acid, had the greatest antifungal activity. 5b showed iron(II)-chelating properties and reduced ergosterol content in C. fimbriata cells, causing irregularities in the fungal cell wall and inhibiting conidia agglutination. Application of 3 mm 5b reduced black rot symptoms in sweet potatoes by 70.1%.

CONCLUSIONS

Collectively, derivatization of the carboxylic acid from quinic acid was demonstrated to be a suitable strategy to improve the antifungal properties of this compound. This study reveals a new efficient strategy for management of the sweet potato pathogen C. fimbriata. © 2024 Society of Chemical Industry.

Unlocking Nature's Shield: The Promising Potential of CRISPRa in Amplifying Antimicrobial Peptide Expression in Common Bean (Phaseolus vulgaris L.)

This study proposes using the CRISPR transcriptional activation strategy to modulate the expression of genes encoding defense proteins and antimicrobial peptides (AMPs) in Phaseolus vulgaris. Three genes (PvD1, Pv-thionin, and Pv-lectin) were selected and targeted by the CRISPR-dCas9-TV-mediated transcriptional activation complex in the P. vulgaris L. hairy root. RT-qPCR investigated their activation efficiency. The eGFP-positive transgenic hairy roots exhibit enhanced expression of targeted genes compared to that of control roots. A moderate increase of 1.37-fold in PvD1 gene expression was observed in transgenic hairy roots, while 6.97-fold (Pv-lectin) and 5.70-fold (Pv-thionin) increases were observed. Importantly, no off-target effects of sgRNAs were detected, ensuring the precision and safety of the CRISPR-dCas9-TV strategy. The present article is a proof-of-concept study, and it has succeeded in demonstrating the efficiency of the CRISPR-dCas9-TV strategy in modulating the expression of target genes in P. vulgaris, paving the way for an alternative approach to protecting such essential crop plants.

Deciphering the Distinct Associations of Rhizospheric and Endospheric Microbiomes with Capsicum Plant Pathological Status

Exploring endospheric and rhizospheric microbiomes and their associations can help us to understand the pathological status of capsicum (Capsicum annuum L.) for implementing appropriate management strategies. To elucidate the differences among plants with distinct pathological status in the communities and functions of the endospheric and rhizospheric microbiomes, the samples of healthy and diseased capsicum plants, along with their rhizosphere soils, were collected from a long-term cultivation field. The results indicated a higher bacterial richness in the healthy rhizosphere than in the diseased rhizosphere (P < 0.05), with rhizospheric bacterial diversity surpassing endospheric bacterial diversity. The community assemblies of both the endospheric and rhizospheric microbiomes were driven by a combination of stochastic and deterministic processes, with the stochastic processes playing a primary role. The majority of co-enriched taxa in the healthy endophyte and rhizosphere mainly belonged to bacterial Proteobacteria, Actinobacteria, and Firmicutes, as well as fungal Ascomycota. Most of the bacterial indicators, primarily Alphaproteobacteria and Actinobacteria, were enriched in the healthy rhizosphere, but not in the diseased rhizosphere. In addition, most of the fungal indicators were enriched in both the healthy and diseased endosphere. The diseased endophyte constituted a less complex and stable microbial community than the healthy endophyte, and meanwhile, the diseased rhizosphere exhibited a higher complexity but lower stability than the healthy rhizosphere. Notably, only a microbial function, namely biosynthesis of other secondary metabolites, was higher in the healthy endophytes than in the diseased endophyte. These findings indicated the distinct responses of rhizospheric and endospheric microbiomes to capsicum pathological status, and in particular, provided a new insight into leveraging soil and plant microbial resources to enhance agriculture production.

Antifungal peptides: Therapeutic potential and challenges before their commercial success

Antifungal peptides (AFPs) are small cationic peptides that are found in a diverse range of taxa including bacteria, plants, mammals and insects. AFPs exhibit the strong antifungal activities against several pathogenic fungi, making them potential candidates for developing novel antifungal agents. AFP cause fungal cell death by rupturing the membranes of the fungal cell wall and inhibits the vital enzymes. Since AFPs are isolated from a range of natural sources, efforts are being made to create synthetic versions of these peptides with improved pharmacological properties. One of their key advantages is that they are less likely to develop resistance as compared to conventional antifungal medications. Although AFPs display immense potential as antifungal agents, challenges still exist in their stability, solubility, absorption, and time-consuming extraction process. Still, the possibility for AFPs to evolve into a novel class of antifungal medicine gives hope for improved treatments for fungal infections. This article offers the comprehensive information on AFPs origin, mode of action, prospective use in antifungal treatments. It also discusses about the application of antifungal peptides beyond the therapeutic field, such as in agriculture for crop protection, in food industry and in aquaculture field. It further elaborates on the challenges and potential paths associated with the progression of AFPs as advanced antifungal agents.

Antifungal peptides from living organisms

In the post-COVID-19 era, people are increasingly concerned about microbial infections, including fungal infections that have risen in recent years. However, the currently available antifungal agents are rather limited. Worse still, the widespread use of the antifungal agents has caused the emergence of antifungal resistance in Candida, Cryptococcus, and Aspergillus species. Therefore, the development of novel antifungals is urgently needed. Antimicrobial peptides (AMPs), as components of the first-line defense of the host, are found to exhibit broad antimicrobial activity against bacteria, fungi, parasites, viruses, and protozoa. AMPs with antifungal activity are specifically referred to as antifungal peptides (AFPs). AFPs are currently regarded as the most promising alternative to conventional antifungal agents due to the fact that they are highly selective and less prone to facilitate the selection of drug resistance. In this review, we present an overview of the origin and classification of natural AFPs as well as their modes of action. Additionally, the production of natural, semisynthetic, and synthetic AFPs with a view to greater levels of exploitation is discussed. Finally, we evaluate the current and potential applications of AFPs in clinics and in the food industry.

Plant growth-promoting microorganisms drive K strategists through deterministic processes to alleviate biological stress caused by Fusarium oxysporum

Soybean root rot, caused by soil-borne pathogens such as Fusarium oxysporum, frequently occurs in Northeast China and leads to a decline in soil health and becoming a bottleneck for soybean yield in the region. To address this issue, applying beneficial microorganisms and altering soil microbial community structure have become effective strategies. In this study, the 90-day soybean pot experiment was conducted to explore the assembly process and life strategy selection of bacterial communities in the rhizosphere of healthy (inoculated with Funneliformis mosseae, F group and treated with Pseudomonas putida, P group) and diseased (inoculated with F. oxysporum, O group) soybean plants, as well as the recovery effect of beneficial microorganisms on soil-borne diseases (combined treatments OP and OF). Results indicated that in healthy soils (P and F), microbial community assembly process in the soybean rhizosphere was entirely governed by heterogeneous selection (HeS, 100 %). However, inoculated with P. putida (OP) was primarily driven by stochastic processes (HeS 40 %, dispersal limitation (DL) 60 %), and the F. mosseae treatment (OF) predominantly followed a deterministic process (HeS 89 %, DL 11 %) in diseased soils. Inoculation of plant growth-promoting microorganisms (PGPMs) in diseased soil drove the life strategy of the rhizosphere bacterial community from r- to K-strategy, evident from the lower rRNA operon (rrn) copy numbers (O 3.7, OP 2.1, OF 2.3), higher G+ to G- ratios (O 0.47, OP 0.58, OF 0.57), and a higher abundance of oligotrophs (O 50 %, OP 53 %, OF 54 %). In healthy (P and F) and diseased (O, OP, OF) rhizosphere soils, OTU820, OTU6142, and OTU8841 under the K-strategy, and OTU6032 and OTU6917 under the r-strategy, which served as keystone species, had a significant promoting relationship with plant biomass and defense capabilities ( p ＜0.05). Additionally, inoculation of PGPMs improved autotoxin degradation and positively correlated with bacterial life strategies in both healthy and diseased soils (P, F, OP and OF) ( p ＜0.05). These findings enhance our understanding of soil-microbe interactions and offer new insights and precise control measures for soybean disease management and soil environment remediation.

Actinomycetes are a natural resource for sustainable pest control and safeguarding agriculture

Actinomycetes, a diverse group of bacteria with filamentous growth characteristics, have long captivated researchers and biochemists for their prolific production of secondary metabolites. Among the myriad roles played by actinomycete secondary metabolites, their historical significance in the field of biocontrol stands out prominently. The fascinating journey begins with the discovery of antibiotics, where renowned compounds like streptomycin, tetracycline, and erythromycin revolutionized medicine and agriculture. The history of biocontrol traces its roots back to the early twentieth century, when scientists recognized the potential of naturally occurring agents to combat pests and diseases. The emergence of synthetic pesticides in the mid-twentieth century temporarily overshadowed interest in biocontrol. However, with growing environmental concerns and the realization of the negative ecological impacts of chemical pesticides, the pendulum swung back towards exploring sustainable alternatives. Beyond their historical role as antibiotics, actinomycete-produced secondary metabolites encompass a rich repertoire with biopesticide potential. The classification of these compounds based on chemical structure and mode of action is highlighted, demonstrating their versatility against both plant pathogens and insect pests. Additionally, this review provides in-depth insights into how endophytic actinomycete strains play a pivotal role in biocontrol strategies. Case studies elucidate their effectiveness in inhibiting Spodoptera spp. and nematodes through the production of bioactive compounds. By unraveling the multifunctional roles of endophytic actinomycetes, this review contributes compelling narrative knowledge to the field of sustainable agriculture, emphasizing the potential of these microbial allies in crafting effective, environmentally friendly biocontrol strategies for combating agricultural pests.

Exploring the frontiers of therapeutic breadth of antifungal peptides: A new avenue in antifungal drugs

The growing prevalence of fungal infections alongside rising resistance to antifungal drugs poses a significant challenge to public health safety. At the close of the 2000s, major pharmaceutical firms began to scale back on antimicrobial research due to repeated setbacks and diminished economic gains, leaving only smaller companies and research labs to pursue new antifungal solutions. Among various natural sources explored for novel antifungal compounds, antifungal peptides (AFPs) emerge as particularly promising. Despite their potential, AFPs receive less focus than their antibacterial counterparts. These peptides have been sourced extensively from nature, including plants, animals, insects, and especially bacteria and fungi. Furthermore, with advancements in recombinant biotechnology and computational biology, AFPs can also be synthesized in lab settings, facilitating peptide production. AFPs are noted for their wide-ranging efficacy, in vitro and in vivo safety, and ability to combat biofilms. They are distinguished by their high specificity, minimal toxicity to cells, and reduced likelihood of resistance development. This review aims to comprehensively cover AFPs, including their sources-both natural and synthetic-their antifungal and biofilm-fighting capabilities in laboratory and real-world settings, their action mechanisms, and the current status of AFP research.

ONE-SENTENCE SUMMARY

This comprehensive review of AFPs will be helpful for further research in antifungal research.

Genomic Insights into the Microbial Agent Streptomyces albidoflavus MGMM6 for Various Biotechnology Applications

Microbial biotechnology plays a crucial role in improving industrial processes, particularly in the production of compounds with diverse applications. In this study, we used bioinformatic approaches to analyze the genomic architecture of Streptomyces albidoflavus MGMM6 and identify genes involved in various metabolic pathways that have significant biotechnological potential. Genome mining revealed that MGMM6 consists of a linear chromosome of 6,932,303 bp, with a high G+C content of 73.5%, lacking any plasmid contigs. Among the annotated genes, several are predicted to encode enzymes such as dye peroxidase, aromatic ring-opening dioxygenase, multicopper oxidase, cytochrome P450 monooxygenase, and aromatic ring hydroxylating dioxygenases which are responsible for the biodegradation of numerous endogenous and xenobiotic pollutants. In addition, we identified genes associated with heavy metal resistance, such as arsenic, cadmium, mercury, chromium, tellurium, antimony, and bismuth, suggesting the potential of MGMM6 for environmental remediation purposes. The analysis of secondary metabolites revealed the presence of multiple biosynthesis gene clusters responsible for producing compounds with potent antimicrobial and metal-chelating activities. Furthermore, laboratory tests conducted under controlled conditions demonstrated the effectiveness of MGMM6 in inhibiting phytopathogenic microbes, decolorizing and degrading aromatic triphenylmethane dyes, particularly Blue Brilliant G250, from wastewater by up to 98 ± 0.15%. Overall, the results of our study highlight the promising biotechnological potential of S. albidoflavus MGMM6.

A peptide encoded by a highly conserved gene belonging to the genus Streptomyces shows antimicrobial activity against plant pathogens

The genus Streptomyces has been unceasingly highlighted for the versatility and diversity of the antimicrobial agents they produce. Moreover, it is a heavily sequenced taxon in the phylum Actinobacteria. In this study, 47 sequence profiles were identified as proteins highly conserved within the genus Streptomyces. Significant hits to the 38 profiles were found in more than 2000 Streptomyces genomes, 11 of which were further conserved in more than 90% of Actinobacterial genomes analyzed. Only a few genes corresponding to these sequence profiles were functionally characterized, which play regulatory roles in the morphology and biosynthesis of antibiotics. Here a highly conserved sequence, namely, SHC-AMP (Streptomyces highly conserved antimicrobial peptide), which exhibited antimicrobial activity against bacterial and fungal plant pathogens, was reported. In particular, Arabidopsis thaliana was effectively protected against infection with Pseudomonas syringae pv. tomato DC3000 by treatment with this peptide. Results indicated the potential application of this peptide as an antimicrobial agent for control of plant diseases. Our results suggest putative target genes for controlling Streptomyces spp., including the one exhibiting antimicrobial activity against a wide range of phytopathogens.

Functional Peptides for Plant Disease Control

Plant disease control requires novel approaches to mitigate the spread of and losses caused by current, emerging, and re-emerging diseases and to adapt plant protection to global climate change and the restrictions on the use of conventional pesticides. Currently, disease management relies mainly on biopesticides, which are required for the sustainable use of plant-protection products. Functional peptides are candidate biopesticides because they originate from living organisms or are synthetic analogs and provide novel mechanisms of action against plant pathogens. Hundreds of compounds exist that cover an extensive range of activities against viruses, bacteria and phytoplasmas, fungi and oomycetes, and nematodes. Natural sources, chemical synthesis, and biotechnological platforms may provide peptides at large scale for the industry and growers. The main challenges for their use in plant disease protection are (a) the requirement of stability in the plant environment and counteracting resistance in pathogen populations, (b) the need to develop suitable formulations to increase their shelf life and methods of application, (c) the selection of compounds with acceptable toxicological profiles, and (d) the high cost of production for agricultural purposes. In the near future, it is expected that several functional peptides will be commercially available for plant disease control, but more effort is needed to validate their efficacy at the field level and fulfill the requirements of the regulatory framework.

Identification of In Vitro Inhibitors of Monkeypox Replication

Monkeypox virus (MPXV) infections in humans have historically been restricted to regions of endemicity in Africa. However, in 2022, an alarming number of MPXV cases were reported globally, with evidence of person-to-person transmission. Because of this, the World Health Organization (WHO) declared the MPXV outbreak a public health emergency of international concern. The supply of MPXV vaccines is limited, and only two antivirals, tecovirimat and brincidofovir, approved by the U.S. Food and Drug Administration (FDA) for the treatment of smallpox, are currently available for the treatment of MPXV infection. Here, we evaluated 19 compounds previously shown to inhibit different RNA viruses for their ability to inhibit orthopoxvirus infections. We first used recombinant vaccinia virus (rVACV) expressing fluorescence (mScarlet or green fluorescent protein [GFP]) and luciferase (Nluc) reporter genes to identify compounds with antiorthopoxvirus activity. Seven compounds from the ReFRAME library (antimycin A, mycophenolic acid, AVN-944, pyrazofurin, mycophenolate mofetil, azaribine, and brequinar) and six compounds from the NPC library (buparvaquone, valinomycin, narasin, monensin, rotenone, and mubritinib) showed inhibitory activity against rVACV. Notably, the anti-VACV activity of some of the compounds in the ReFRAME library (antimycin A, mycophenolic acid, AVN-944, mycophenolate mofetil, and brequinar) and all the compounds from the NPC library (buparvaquone, valinomycin, narasin, monensin, rotenone, and mubritinib) were confirmed with MPXV, demonstrating their inhibitory activity in vitro against two orthopoxviruses. IMPORTANCE Despite the eradication of smallpox, some orthopoxviruses remain important human pathogens, as exemplified by the recent 2022 monkeypox virus (MPXV) outbreak. Although smallpox vaccines are effective against MPXV, access to those vaccines is limited. In addition, current antiviral treatment against MPXV infections is limited to the use of the FDA-approved drugs tecovirimat and brincidofovir. Thus, there is an urgent need to identify novel antivirals for the treatment of MPXV infection and other potentially zoonotic orthopoxvirus infections. Here, we show that 13 compounds, derived from two different libraries, previously found to inhibit several RNA viruses, also inhibit VACV. Notably, 11 compounds also displayed inhibitory activity against MPXV.

Cyclic Peptides with Antifungal Properties Derived from Bacteria, Fungi, Plants, and Synthetic Sources

Fungal infections remain a significant concern for human health. The emergence of microbial resistance, the improper use of antimicrobial drugs, and the need for fewer toxic antifungal treatments in immunocompromised patients have sparked substantial interest in antifungal research. Cyclic peptides, classified as antifungal peptides, have been in development as potential antifungal agents since 1948. In recent years, there has been growing attention from the scientific community to explore cyclic peptides as a promising strategy for combating antifungal infections caused by pathogenic fungi. The identification of antifungal cyclic peptides from various sources has been possible due to the widespread interest in peptide research in recent decades. It is increasingly important to evaluate narrow- to broad-spectrum antifungal activity and the mode of action of synthetic and natural cyclic peptides for both synthesized and extracted peptides. This short review aims to highlight some of the antifungal cyclic peptides isolated from bacteria, fungi, and plants. This brief review is not intended to present an exhaustive catalog of all known antifungal cyclic peptides but rather seeks to showcase selected cyclic peptides with antifungal properties that have been isolated from bacteria, fungi, plants, and synthetic sources. The addition of commercially available cyclic antifungal peptides serves to corroborate the notion that cyclic peptides can serve as a valuable source for the development of antifungal drugs. Additionally, this review discusses the potential future of utilizing combinations of antifungal peptides from different sources. The review underscores the need for the further exploration of the novel antifungal therapeutic applications of these abundant and diverse cyclic peptides.

Biocontrol potential of Chitinophaga flava HK235 producing antifungal-related peptide chitinocin

Botrytis cinerea is a necrotrophic fungal pathogen with an extremely broad host range, causing significant economic losses in agricultural production. In this study, we discovered a culture filtrate of bacterial strain HK235, which was identified as Chitinophaga flava, exhibiting high levels of antifungal activity against B. cinerea. From the HK235 culture filtrate, we isolated a new antimicrobial peptide molecule designated as chitinocin based on activity-guided fractionation followed by characterization of the amino acid composition and spectroscopic analyses. The HK235 culture filtrate and chitinocin completely inhibited both conidial germination and mycelial growth of B. cinerea at a concentration of 20% and 200 μg/mL, respectively. In addition to antibiosis against B. cinerea, the active compound chitinocin had a broad antifungal and antibacterial activity in vitro. When tomato plants were treated with the culture filtrate and chitinocin, the treatment strongly reduced the development of gray mold disease in a concentration-dependent manner compared to the untreated control. Here, considering the potent antifungal property in vitro and in vivo, we present the biocontrol potential of C. flava HK235 for the first time.

Exploring the antimicrobial, antiviral, antioxidant, and antitumor potentials of marine Streptomyces tunisiensis W4MT573222 pigment isolated from Abu-Qir sediments, Egypt

Due to the therapeutic importance of microbial pigments, these pigments are receiving the attention of researchers. In this present study 60 isolates were isolated from sediments of Abu-Qir coast of the Mediterranean sea, Alexandria, Egypt, out of which 12 were considered as pigmented actinomycetes. Streptomyces sp. W4 was characterized by small round green pigmented colonies when grown on starch-casein agar medium. The green pigment was extracted using a mixture of acetone-methanol (7:3 v/v). The antimicrobial, antioxidant, antiviral, and anticancer activities of the green pigment produced by Streptomyces sp.W4 were investigated. The pigment was characterized using FTIR, Raman spectroscopy, EDX and GC-MS. The results revealed that the pigment has antibacterial and antifungal activity and also showed inhibition of HAV 78% but its antiviral activity against the Adenovirus was weak. The results proved the safety of the pigment toward normal cells and anticancer activity against three different cancer cell lines HepG-2 (liver cancer cell line), A549 (lung cancer cell line), and PAN1 (pancreas cancer cell line). The pigment was combined with 9 antibiotics and then tested against the Gram-negative bacterium Enterococcus faecalis using disc diffusion bioassay. LEV showed an antagonistic effect, while CXM and CIP showed a synergistic effect.

Antivirals against monkeypox infections

Monkeypox virus (MPXV) infection in humans are historically restricted to endemic regions in Africa. However, in 2022, an alarming number of MPXV cases have been reported globally with evidence of person-to-person transmission. Because of this, the World Health Organization (WHO) declared the MPXV outbreak a public health emergency of international concern. MPXV vaccines are limited and only two antivirals, tecovirimat and brincidofovir, approved by the United States (US) Food and Drug Administration (FDA) for the treatment of smallpox, are currently available for the treatment of MPXV infection. Here, we evaluated 19 compounds previously shown to inhibit different RNA viruses for their ability to inhibit Orthopoxvirus infections. We first used recombinant vaccinia virus (rVACV) expressing fluorescence (Scarlet or GFP) and luciferase (Nluc) reporter genes to identify compounds with anti-Orthopoxvirus activity. Seven compounds from the ReFRAME library (antimycin A, mycophenolic acid, AVN- 944, pyrazofurin, mycophenolate mofetil, azaribine, and brequinar) and six compounds from the NPC library (buparvaquone, valinomycin, narasin, monensin, rotenone, and mubritinib) showed antiviral activity against rVACV. Notably, the anti-VACV activity of some of the compounds in the ReFRAME library (antimycin A, mycophenolic acid, AVN- 944, mycophenolate mofetil, and brequinar) and all the compounds from the NPC library (buparvaquone, valinomycin, narasin, monensin, rotenone, and mubritinib) were confirmed with MPXV, demonstrating the broad-spectrum antiviral activity against Orthopoxviruses and their potential to be used for the antiviral treatment of MPXV, or other Orthopoxvirus, infections.

IMPORTANCE

Despite the eradication of smallpox, some Orthopoxviruses remain important human pathogens, as exemplified by the recent 2022 monkeypox virus (MPXV) outbreak. Although smallpox vaccines are effective against MPXV, there is presently limited access to those vaccines. In addition, current antiviral treatment against MPXV infections is limited to the use of the FDA-approved drugs tecovirimat and brincidofovir. Thus, there is an urgent need to identify novel antivirals for the treatment of MPXV, and other potentially zoonotic Orthopoxvirus infections. Here, we show that thirteen compounds, derived from two different libraries, previously found to inhibit several RNA viruses, exhibit also antiviral activity against VACV. Notably, eleven compounds also displayed antiviral activity against MPXV, demonstrating their potential to be incorporated into the therapeutic armamentarium to combat Orthopoxvirus infections.

Occurrence of Streptomyces tauricus in mangrove soil of Mangalore region in Dakshina Kannada as a source for antimicrobial peptide

Microbial resistance and deprivation of the effective drugs have become the foremost problem that propels to seek out for advanced approach. This concept initiated a need to search for more effective antimicrobial compounds from reliable sources. The Streptomyces is grouped under phylum Actinobacteria and are considered prolific producers of antibiotics, around 70% of presently available antibiotics are contributed by Streptomyces alone. In this study, Mangroves of the Mangalore Coast offered a unique source for screening Actinomyces group of microorganisms. We investigated on the four soil samples collected from Mangrove swamps of Mangalore, Karnataka, India. Based on their culture traits, the 18 distinct Actinomyces isolates were analyzed through a series of morphological and biochemical tests on starch casein nitrate (SCN) media. Culture biomasses were subjected for intracellular protein extraction through acetone precipitation method; the extracted proteins from each Actinomyces isolate were examined for antimicrobial activity against test organisms. The isolate ANTB-YKMU4 showed potential antimicrobial activity against significant number of test organisms; Bacillus cereus, Proteus vulgaris, Staphylococcus aureus, Salmonella typhimurium, and Pseudomonas aeruginosa. The isolate ANTB-YKMU4 through 16 s rRNA gene sequence analysis was identified as Streptomyces tauricus strain with GenBank accession no. MW785875.1. The S. tauricus further cultivated for efficient biomass growth on SCN media for subsequent protein extraction and purification by a series of Electrophoretic and chromatographic techniques. Thus, by intracellular extractions from S. tauricus resulted in the identification of peptide with a molecular weight of 266 Da that was characterized by LC-MS.

Antiproliferative activity of antimicrobial peptides and bioactive compounds from the mangrove Glutamicibacter mysorens

The Glutamicibacter group of microbes is known for antibiotic and enzyme production. Antibiotics and enzymes produced by them are important in the control, protection, and treatment of chronic human diseases. In this study, the Glutamicibacter mysorens (G. mysorens) strain MW647910.1 was isolated from mangrove soil in the Mangalore region of India. After optimization of growth conditions for G. mysorens on starch casein agar media, the micromorphology of G. mysorens was found to be spirally coiled spore chain, each spore visualized as an elongated cylindrical hairy appearance with curved edges visualized through Field Emission Scanning Electron Microscopy (FESEM) analysis. The culture phenotype with filamentous mycelia, brown pigmentation, and ash-colored spore production was observed. The intracellular extract of G. mysorens characterized through GCMS analysis detected bioactive compounds reported for pharmacological applications. The majority of bioactive compounds identified in intracellular extract when compared to the NIST library revealed molecular weight ranging below 1kgmole^-1. The Sephadex G-10 could result in 10.66 fold purification and eluted peak protein fraction showed significant anticancer activity on the prostate cancer cell line. Liquid Chromatography-Mass Spectrometry (LC-MS) analysis revealed Kinetin-9-ribose and Embinin with a molecular weight below 1 kDa. This study showed small molecular weight bioactive compounds produced from microbial origin possess dual roles, acting as antimicrobial peptides (AMPs) and anticancer peptides (ACPs). Hence, the bioactive compounds produced from microbial origin are a promising source of future therapeutics.

Identification and genomic analyses of a novel endophytic actinobacterium Streptomyces endophytica sp. nov. with potential for biocontrol of yam anthracnose

Anthracnose disease caused by Colletotrichum gloeosporioides is one of the devastating diseases of yams (Dioscorea sp.) worldwide. In this study, we aimed to isolate endophytic actinobacteria from yam plants and to evaluate their potential for the control of yam anthracnose based on bioassays and genomic analyses. A total of 116 endophytic actinomycete strains were isolated from the surface-sterilized yam tissues from a yam orchard in Hainan Province, China. In total, 23 isolates showed antagonistic activity against C. gloeosporioides. An endophytic actinomycete, designated HNM0140^T, which exhibited strong antifungal activities, multiple biocontrol, and plant growth-promoting (PGP) traits was subsequently selected to colonize in the tissue-cultured seedlings of yam and was tested for its in vivo biocontrol potential on yam anthracnose. The results showed that treatment with strain HNM0140^T markedly reduced the severity and incidence of yam anthracnose under greenhouse conditions. Morphological and chemotaxonomic analyses showed that strain HNM0140^T was assigned to the genus Streptomyces. Phylogenetic analysis based on the 16S rRNA gene sequences indicated that strain HNM0140^T formed a separate cluster together with Streptomyces lydicus ATCC 25470^T (99.45%), Streptomyces chattanoogensis NRRL ISP-5002^T (99.45%), and Streptomyces kronopolitis NEAU-ML8^T (98.97%). The phylogenomic tree also showed that strain HNM0140^T stably clustered with Streptomyces lydicus ATCC 25470^T. The ANI and dDDH between strain HNM0140^T and its closest related-type species were well below the recommended thresholds for species demarcation. Hence, based on the phylogenetic, genomic, and phenotypic analyses, strain HNM0140^T should represent a new streptomycete species named Streptomyces endophytica sp. nov. Genomic analysis revealed that strain HNM0140^T harbored 18 putative BGCs for secondary metabolites, some PGP-related genes, and several genes coding for antifungal enzymes. The presented results indicated that strain HNM0140^T was a promising biocontrol agent for yam anthracnose.

Expression of Immunity- and Stress-Related Genes during an Intermolt Period in the Colorado Potato Beetle

Different developmental stages of insects may be dissimilar in immunity functioning. Additionally, the stages often inhabit diverse environments with specific microbial communities. In the Colorado potato beetle, a strong increase in resistance to entomopathogenic fungi is observed during the intermolt period of last-instar larvae, but mechanisms of this change are insufficiently understood. We studied changes in the expression of immunity- and stress-related genes in the fat body and integument during this intermolt period by quantitative PCR. By the end of the instar, there was upregulation of transcription factors of Toll, IMD, and Jak-Stat pathways as well as genes encoding metalloprotease inhibitors, odorant-binding proteins, and heat shock proteins. Nonetheless, the expression of gene LdRBLk encoding β-lectin did not change during this period. Most of the aforementioned genes were upregulated in response to Metarhizium robertsii topical infection. The expression alterations were more pronounced in recently molted larvae than in finishing feeding larvae and in the integument compared to the fat body. We believe that upregulation of immune-system- and stress-related genes at the end of the intermolt period is an adaptation caused by migration of larvae into soil, where the probability of encountering entomopathogenic fungi is high.

His-Ala-Phe-Lys peptide from Burkholderia arboris possesses antifungal activity

Burkholderia arboris, which belongs to the Burkholderia cepacia complex, has been shown to possess antifungal activity against several plant fungal pathogens; however, the antifungal compounds are yet to be identified. Here, we identified the antifungal compounds produced by B. arboris using genetic and metabolomic approaches. We generated a Tn5 transposon mutation library of 3,000 B. arboris mutants and isolated three mutants with reduced antifungal activity against the plant fungal pathogen Fusarium oxysporum. Among the mutants, the M464 mutant exhibited the weakest antifungal activity. In the M464 genome, the transposon was inserted into the cobA gene, encoding uroporphyrin-III methyltransferase. Deletion of the cobA gene also resulted in reduced antifungal activity, indicating that the cobA gene contributed to the antifungal activity of B. arboris. Furthermore, a comparison of the differential metabolites between wild type B. arboris and the ∆cobA mutant showed a significantly decreased level of tetrapeptide His-Ala-Phe-Lys (Hafk) in the ∆cobA mutant. Therefore, a Hafk peptide with D-amino acid residues was synthesized and its antifungal activity was evaluated. Notably, the Hafk peptide displayed significant antifungal activity against F. oxysporum and Botrytis cinerea, two plant pathogens that cause destructive fungal diseases. Overall, a novel antifungal compound (Hafk) that can be used for the biocontrol of fungal diseases in plants was identified in B. arboris.

Actinomycete Potential as Biocontrol Agent of Phytopathogenic Fungi: Mechanisms, Source, and Applications

Synthetic fungicides have been the main control of phytopathogenic fungi. However, they cause harm to humans, animals, and the environment, as well as generating resistance in phytopathogenic fungi. In the last few decades, the use of microorganisms as biocontrol agents of phytopathogenic fungi has been an alternative to synthetic fungicide application. Actinomycetes isolated from terrestrial, marine, wetland, saline, and endophyte environments have been used for phytopathogenic fungus biocontrol. At present, there is a need for searching new secondary compounds and metabolites of different isolation sources of actinomycetes; however, little information is available on those isolated from other environments as biocontrol agents in agriculture. Therefore, the objective of this review is to compare the antifungal activity and the main mechanisms of action in actinomycetes isolated from different environments and to describe recent achievements of their application in agriculture. Although actinomycetes have potential as biocontrol agents of phytopathogenic fungi, few studies of actinomycetes are available of those from marine, saline, and wetland environments, which have equal or greater potential as biocontrol agents than isolates of actinomycetes from terrestrial environments.

Optimization of fermentation medium and conditions for enhancing valinomycin production by Streptomyces sp. ZJUT-IFE-354

Valinomycin is a cyclodepsipeptide antibiotic with a broad spectrum of biological activities, such as antiviral, antitumor, and antifungal activities. However, the low yield of valinomycin often limits its applications in medicine, agriculture, and industry. In our previous report, Streptomyces sp. ZJUT-IFE-354 was identified as a high-yielding strain of valinomycin. In this study, Plackett-Burman design (PBD) and response surface methodology (RSM) were used to optimize components of medium. The optimal medium contained 31 g/L glucose, 22 g/L soybean meal, and 1.6 g/L K₂HPO₄·3H₂O, which could generate 262.47 ± 4.28 mg/L of valinomycin. Then, the culture conditions were optimized by a one-factor-at-a-time (OFAT) approach. The optimal conditions for the strain included a seed age of 24 h, an inoculum size of 8% (v/v), an incubation temperature of 28 °C, an initial pH of 7.2, an elicitor of 0.1% Bacillus cereus feeding at 24 h cultivation, and the feeding of 0.6% _L-valine at 36 h cultivation. The final valinomycin production increased to 457.23 ± 9.52 mg/L, which was the highest yield ever reported. It highlights that RSM and OFAT may be efficient methods to enhance valinomycin production by Streptomyces sp. ZJUT-IFE-354.

Efficient production of valinomycin by the soil bacterium, Streptomyces sp. ZJUT-IFE-354

A novel strain with antifungal activity against Sclerotinia sclerotiorum was isolated from soil, and identified as Streptomyces sp. ZJUT-IFE-354 using morphological and 16S rDNA sequence analysis. The bioactive metabolite produced by strain ZJUT-IFE-354 was identified and characterized as valinomycin by spectroscopic and chemical methods. The yield of valinomycin was 191.26 mg/L from the culture of Streptomyces sp. ZJUT-IFE-354, which was the highest yield to our knowledge. The in vitro antifungal activity of valinomycin against S. sclerotiorum was investigated as 0.056 ± 0.012 (EC₅₀) and 0.121 ± 0.023 μg/mL (EC₉₅), respectively, which was approximately 10.696- and 30.960-fold more active than that of carbendazim. The results from scanning electron microscopy, cell membrane permeability, and _D-sorbitol and ergosterol assay indicated that valinomycin exerted the antifungal activity probably by increasing permeability of fungal cell membrane, leading to mycelial electrolyte leakage, and eventually resulting in the death of S. sclerotiorum. Thus, valinomycin may be a promising antifungal agent to control S. sclerotiorum.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-021-03055-5.

Maleimide structure: a promising scaffold for the development of antimicrobial agents

Natural compounds bearing maleimide rings are a series of secondary metabolites derived from fungi/marine microorganisms, which are characterized by a general structure -CO-N(R)-CO-, and the R group is normally substituted with alkyl or aryl groups. Maleimide compounds show various biological activities such as antibacterial, antifungal, and anticancer activity. In this review, the broad-spectrum antimicrobial activities of 15 maleimide compounds from natural sources and 32 artificially synthesized maleimides were summarized, especially against Candida albicans, Sclerotinia sclerotiorum, and Staphylococcus aureus. It highlights that maleimide scaffold has tremendous potential to be utilized in the development of novel antimicrobial agents.

Biological control of fungal pathogens of tomato (Lycopersicon esculentum) by chitinolytic bacterial strains

The need to increase food production and to reduce the pollution caused by synthetic chemicals has led to a search for biocontrol agents against plant pathogens. In the present study, a total of 37 chitinolytic bacteria were isolated from the rhizospheric soil of tomatoes using a chitin agar medium. In vitro bacterial isolates, that is, TD9, TD11, TD15, and TD24 showed strong antagonistic and enzymatic activities against Rhizoctonia (8%-55%), Fusarium (31%-48%), Colletotrichum (24%-49%), and Aspergillus on a dual culture plate and enzyme assay. Furthermore, these putative antagonistic bacterial isolates were identified as Pantoea agglomerans (TD9), Bacillus subtilis (TD11), Bacillus cereus (TD15 and TD24) using 16S rRNA sequence analysis. Additionally, in culture filtrate in vivo assay, the isolates TD11 and TD15 inhibited the growth of Rhizoctonia solani about 40% and Fusarium oxysporum about 80%. However, in the pot trials, these two bacterial isolates (TD11 and TD15) considerably suppressed the disease rate in tomatoes caused by Fusarium and Rhizoctonia fungal species. Moreover, it was concluded that B. subtilis (TD11) was found to be the most promising putative biocontrol agent, inhibiting the fungal diseases of tomatoes by 50% and showing versatile antagonistic potential.

Bioactive antifungal metabolites produced by Streptomyces amritsarensis V31 help to control diverse phytopathogenic fungi

Actinomycetes due to their unique repertoire of antimicrobial secondary metabolites can be an eco-friendly and sustainable alternative to agrochemicals to control plant pathogens. In the present study, antifungal activity of twenty different actinomycetes was evaluated via dual culture plate assay against six different phytopathogens, viz., Alternaria alternata, Aspergillus flavus, Fusarium oxysporum f. sp. lycopersici, Sarocladium oryzae, Sclerotinia sclerotiorum, and Rhizoctonia solani. Two potential isolates, Streptomyces amritsarensis V31 and Kribella karoonensis MSCA185 showing high antifungal activity against all six fungal pathogens, were further evaluated after extraction of bioactive metabolites in different solvents. Metabolite extracted from S. amritsarensis V31 in different solvents inhibited Rhizoctonia solani (7.5-65%), Alternaria alternata (5.5-52.7%), Aspergillus flavus (8-30.7%), Fusarium oxysporum f. sp. lycopersici (25-44%), Sarocladium oryzae (11-55.5%), and Sclerotinia sclerotiorum (29.7-40.5%); 1000 D diluted methanolic extract of S. amritsarensis V31 showed growth inhibition against R. solani (23.3%), A. flavus (7.7%), F. oxysporum (22.2%), S. oryzae (16.7%), and S. sclerotiorum (19.0%). Metabolite extracts of S. amritsarensis V31 significantly reduced the incidence of rice sheath blight both as preventive and curative sprays. Chemical profiling of the metabolites in DMSO extract of S. amritsarensis V31 revealed 6-amino-5-nitrosopyrimidine-2,4-diol as the predominant compound present. It was evident from the LC-MS analyses that S. amritsarensis V31 produced a mixture of potential antifungal compounds which inhibited the growth of different phytopathogenic fungi. The results of this study indicated that metabolite extracts of S. amritsarensis V31 can be exploited as a bio-fungicide to control phytopathogenic fungi.

Anti-leishmanial compounds from microbial metabolites: a promising source

Leishmania is a complex disease caused by the protozoan parasites and transmitted by female phlebotomine sandfly. The disease affects some of the poorest people on earth with an estimated 700,000 to 1 million new cases annually. The current treatment for leishmaniasis is toxic, long, and limited, in view of the high resistance rate presented by the parasite, necessitating new perspectives for treatment. The discovery of new compounds with different targets can be a hope to make the treatment more efficient. Microbial metabolites and their structural analogues with enormous scaffold diversity and structural complexity have historically played a key role in drug discovery. We found thirty-nine research articles published between 1999 and 2021 in the scientific database (PubMed, Science Direct) describing microbes and their metabolites with activity against leishmanial parasites which is the focus of this review. KEY POINTS: • Leishmania affects the poorest regions of the globe • Current treatments for leishmaniasis are toxic and of limited efficacy • Microbial metabolites are potential sources of antileishmania drugs.

Elicitation of Streptomyces lunalinharesii secondary metabolism through co-cultivation with Rhizoctonia solani

The concern regarding the emergence of phytopathogens strains which are resistant to conventional agrochemicals has given support to the search for alternatives on the use of chemical pesticides in agriculture. In this context, microorganisms are considered as promising sources of useful natural compounds and actinobacteria are particularly relevant since they are known to produce several bioactive metabolites. The objective of this work was to investigate the production of secondary metabolites with antifungal activity by a strain of the actinobacteria Streptomyces lunalinharesii (A54A) under axenic conditions and in co-cultivation with the phytopathogen Rhizoctonia solani. Tests to evaluate antifungal activity of the extracts indicated the presence of diffusable molecules capable of inhibiting the growth of R. solani produced by S. lunalinharesii, especially when in the presence of the fungus during fermentation. Metabolomic analyzes allowed the putative annotation of the bioactive compounds desferrioxamine E and anisomycin, in addition to the evaluation of the metabolic profile of the isolate when grown in axenic mode and in co-cultivation, while statistical analyzes enabled the comparison of such profiles and the identification of metabolites produced in greater relative quantities in the elicitation condition. Such methodologies provided the selection of unknown features with high bioactive potential for dereplication, and several metabolites of S. lunalinharesii possibly represent novel compounds.

Cyclofaulknamycin with the Rare Amino Acid D-capreomycidine Isolated from a Well-Characterized Streptomyces albus Strain

Targeted genome mining is an efficient method of biosynthetic gene cluster prioritization within constantly growing genome databases. Using two capreomycidine biosynthesis genes, alpha-ketoglutarate-dependent arginine beta-hydroxylase and pyridoxal-phosphate-dependent aminotransferase, we identified two types of clusters: one type containing both genes involved in the biosynthesis of the abovementioned moiety, and other clusters including only arginine hydroxylase. Detailed analysis of one of the clusters, the flk cluster from Streptomyces albus, led to the identification of a cyclic peptide that contains a rare D-capreomycidine moiety for the first time. The absence of the pyridoxal-phosphate-dependent aminotransferase gene in the flk cluster is compensated by the XNR_1347 gene in the S. albus genome, whose product is responsible for biosynthesis of the abovementioned nonproteinogenic amino acid. Herein, we report the structure of cyclofaulknamycin and the characteristics of its biosynthetic gene cluster, biosynthesis and bioactivity profile.

Therapeutic Potential of Exploiting Autophagy Cascade Against Coronavirus Infection

Since its emergence in December 2019 in Wuhan, China, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) created a worldwide pandemic of coronavirus disease (COVID-19) with nearly 136 million cases and approximately 3 million deaths. Recent studies indicate that like other coronaviruses, SARS-CoV-2 also hijacks or usurps various host cell machineries including autophagy for its replication and disease pathogenesis. Double membrane vesicles generated during initiation of autophagy cascade act as a scaffold for the assembly of viral replication complexes and facilitate RNA synthesis. The use of autophagy inhibitors - chloroquine and hydroxychloroquine initially appeared to be as a potential treatment strategy of COVID-19 patients but later remained at the center of debate due to high cytotoxic effects. In the absence of a specific drug or vaccine, there is an urgent need for a safe, potent as well as affordable drug to control the disease spread. Given the intricate connection between autophagy machinery and viral pathogenesis, the question arises whether targeting autophagy pathway might show a path to fight against SARS-CoV-2 infection. In this review we will discuss about our current knowledge linking autophagy to coronaviruses and how that is being utilized to repurpose autophagy modulators as potential COVID-19 treatment.

Identification of the Ricin-B-Lectin LdRBLk in the Colorado Potato Beetle and an Analysis of Its Expression in Response to Fungal Infections

Ricin-B-lectins (RBLs) have been identified in many groups of organisms, including coleopterans insects, particularly the Colorado potato beetle Leptinotarsa decemlineata (LdRBLs). We hypothesized that one of these LdRBLs (LdRBLk) may be involved in the immune response to fungal infections. We performed a theoretical analysis of the structure of this protein. Additionally, the expression levels of the LdRBlk gene were measured in L. decemlineata in response to infections with the fungi Metarhizium robertsii and Beauveria bassiana. The expression levels of LdRBlk in the L. decemlineata cuticle and fat body were increased in response to both infections. The induction of LdRBlk expression was dependent on the susceptibility of larvae to the fungi. Upregulation of the LdRBlk gene was also observed in response to other stresses, particularly thermal burns. Elevation of LdRBlk expression was frequently observed to be correlated with the expression of the antimicrobial peptide attacin but was not correlated with hsp90 regulation. Commercially available β-lectin of ricin from Ricinuscommunis was observed to inhibit the germination of conidia of the fungi. We suggest that LdRBLk is involved in antifungal immune responses in the Colorado potato beetle, either exerting fungicidal properties directly or acting as a modulator of the immune response.

Valinomycin as a potential antiviral agent against coronaviruses: A review

Human coronaviruses (HCoVs), including severe acute respiratory syndrome coronavirus (SARS-CoV), Middle East respiratory syndrome coronavirus (MERS-CoV), and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), have been resulting in global epidemics with heavy morbidity and mortality. Unfortunately, there are currently no specific medicines that can better treat these coronaviruses. Drug repurposing is an effective and economical strategy for drug discovery from existing drugs, natural products, and synthetic compounds. In this review, the broad-spectrum antiviral activity of valinomycin (VAL), especially its activity against coronaviruses such as SARS-CoV, MERS-CoV, human coronavirus OC43 (HCoV-OC43), were summarized, it highlights that VAL has tremendous potential for use as a novel antiviral agent against SARS-CoV-2.