Antifungal and antifeedant activities of extracellular product of Streptomyces spp. ERI-04 isolated from Western Ghats of Tamil Nadu

Streptomyces albidoflavus Q antifungal metabolites inhibit the ergosterol biosynthesis pathway and yeast growth in fluconazole-resistant Candida glabrata: phylogenomic and metabolomic analyses

There is an urgent need to develop new antifungals due to the increasing prevalence of multidrug-resistant fungal infections and the recent emergence of COVID-19-associated candidiasis. A good study model for evaluating new antifungal compounds is Candida glabrata, an opportunistic fungal pathogen with intrinsic resistance to azoles (the most common clinical drugs for treating fungal infections). The aim of the current contribution was to conduct in vitro tests of antifungal metabolites produced by the bacteria Streptomyces albidoflavus Q, identify their molecular structures, and utilize several techniques to provide evidence of their therapeutic target. S. albidoflavus was isolated from maize rhizospheric soil in Mexico and identified by phylogenomic analysis using a 92-gene core. Of the 66 metabolites identified in S. albidoflavus Q by a liquid chromatography-high resolution mass spectrometry (LC-HRMS) metabolomic analysis of the lyophilized supernatant, six were selected by the Way2drug server based on their in silico binding to the likely target, 3-hydroxy-3-methyl-glutaryl-CoA reductase (HMGR, the key enzyme in the ergosterol biosynthesis pathway). Molecular modeling studies show a relatively high binding affinity for the CgHMGR enzyme by two secondary metabolites: isogingerenone B (diaryl heptanoid) and notoginsenoside J (polycyclic triterpene). These secondary metabolites were able to inhibit ergosterol synthesis and affect yeast viability in vitro. They also caused alterations in the ultrastructure of the yeast cytoplasmic membrane, as evidenced by transmission electron microscopy. The putative target of isogingerenone B and notoginsenoside J is distinct from that of azole drugs (the most common clinical antifungals). The target for the latter is the lanosterol 14 alpha-demethylase enzyme (Erg11). IMPORTANCE Multidrug resistance has emerged among yeasts of the genus Candida, posing a severe threat to global health. The problem has been exacerbated by the pandemic associated with COVID-19, during which resistant strains of Candida auris and Candida glabrata have been isolated from patients infected with the SARS-CoV-2 virus. To confront this challenge, the World Health Organization has invoked scientists to search for new antifungals with alternative molecular targets. This study identified 66 metabolites produced by the bacteria Streptomyces albidoflavus Q, 6 of which had promising properties for potential antifungal activity. The metabolites were tested in vitro as inhibitors of ergosterol synthesis and C. glabrata growth, with positive results. They were also found to damage the cytoplasmic membrane of the fungus. The corresponding molecular structures and their probable therapeutic target were established. The target is apparently distinct from that of azole drugs.

Diversity and Biotechnological Potential of Marine Actinomycetes from India

Actinomycetes are potential antibiotic producers that have been isolated from various terrestrial ecosystems and are exploited for their bioactive compounds. On the contrary, the marine environments were less explored and the research on marine actinomycetes had gained momentum only for the past three decades. Marine actinomycetes are one of the most significant producers of diverse groups of secondary metabolites and provide a huge scope for pharmaceutical and other industries. These organisms are proved to be important, both biotechnologically and economically considering their global presence. The marine ecosystem in India is less explored for the isolation of actinomycetes and several ecological niches are left unattended. Compared to the global scenario, the contribution from Indian researchers towards the isolation and exploitation of marine actinomycetes from the Indian sub-continent is noteworthy. Exploration of actinomycetes from these ecosystems will certainly yield new species and metabolites. Considering the declining rate of drug discovery from terrestrial actinomycetes, the marine counterparts, especially from unexplored regions from the Indian coast will hold a promising way ahead. Apart from drugs, these organisms are reported for the production of different industrially important enzymes like cellulase, amylase, protease, lipase, etc. They are also used in environmental applications, agriculture, and aquacultures sectors. With the rapid advancement in the study of actinomycetes from different marine sources in India, new metabolites are being discovered which have an important role from the economic and industrial point of view. As the world is witnessing newer diseases such as Sars-Cov 2 and the pandemic due to its demands drugs and other metabolites are increasing day by day. Therefore, the necessity for the quest for unique and rare marine actinomycetes is enhancing too. This review highlights the research on marine actinomycetes in India and also the challenges associated with its research.

Antibacterial Activity of a Novel Oligosaccharide from Streptomyces californics against Erwinia carotovora subsp. Carotovora

The present study aims to characterize and predict models for antibacterial activity of a novel oligosaccharide from Streptomyces californics against Erwinia carotovora subsp. carotovora using an adaptive neuro-fuzzy inference system and an artificial neural network. The mathematical predication models were used to determine the optimal conditions to produce oligosaccharide and determine the relationship between the factors (pH, temperature, and time). The characteristics of the purified antibacterial agent were determined using ultraviolet spectroscopy (UV/Vis), infrared spectroscopy (FT-IR), nuclear magnetic resonance spectroscopy (¹H- and ¹³C-NMR), and mass spectrometry (MS). The best performances for the model were 39.45 and 35.16 recorded at epoch 1 for E. carotovora Erw₅ and E. carotovora EMCC 1687, respectively. The coefficient (R²) of the training was more than 0.90. The highest antimicrobial production was recorded after 9 days at 25 °C and a pH of 6.2, at which more than 17 mm of the inhibition zone was obtained. The mass spectrum of antimicrobial agent (peak at R.T. = 3.433 of fraction 6) recorded two molecular ion peaks at m/z = 703.70 and m/z = 338.30, corresponding to molecular weights of 703.70 and 338.30 g/mol, respectively. The two molecular ion peaks matched well with the molecular formulas C₂₉H₅₃NO₁₈ and C₁₄H₂₆O₉, respectively, which were obtained from the elemental analysis result. A novel oligosaccharide from Streptomyces californics with potential activity against E. carotovora EMCC 1687 and E. carotovora Erw₅ was successfully isolated, purified, and characterized.

Statistical versus artificial intelligence -based modeling for the optimization of antifungal activity against Fusarium oxysporum using Streptomyces sp. strain TN71

A Streptomyces sp. strain TN71 was isolated from Tunisian Saharan soil and selected for its antimicrobial activity against phytopathogenic fungi. In an attempt to increase its anti-Fusarium oxysporum activity, GYM+S (glucose, yeast extract, malt extract and starch) culture medium was selected out of five different production media. Plackett-Burman design (PBD) was used to select yeast extract, malt extract and calcium carbonate (CaCO₃) as parameters having significant effects on antifungal activity, and a Box-Behnken design was applied for further optimization. The analysis revealed that the optimum concentrations for the anti-F. oxysporum activity of the tested variables were yeast extract 5.03g/L, malt extract 8.05g/L and CaCO₃ 4.51g/L. Artificial Neural Networks (ANNs): the Multilayer perceptron (MLP) and the Radial basis function (RBF) were created to predict the anti-F. oxysporum activity. The comparison between experimental and predicted outputs from ANN and Response Surface Methodology (RSM) were studied. The ANN model presents an improvement of 14.73%. To our knowledge, this is the first work reporting the statistical versus artificial intelligence -based modeling for the optimization of bioactive molecules against mycotoxigenic and phytopathogenic fungi.

A non-polyenic antifungal produced by a Streptomyces yatensis strain isolated from Mellah Lake in El Kala, North-East of Algeria

OBJECTIVE

This study aimed at describing one actinomycete strain E65 that was isolated from the water of Mellah Lake in El Kala, North-East of Algeria that produces a non-polyenic antifungal.

MATERIALS AND METHODS

Actinomycetes were isolated from Mellah Lake water and screened for antimicrobial activity. Antimicrobial assays were performed on ISP2 agar. The taxonomic position of the strain E65 was determined regarding phenotypic and 16S DNA sequences features. Time course of antifungal metabolites production was evaluated against Candida albicans on ISP2, ISP1 and GYEA broth. The active antifungal compound was extracted using dichloromethane and revealed by a thin layer of chromatography, chemical reagents, UV-visible and infrared spectroscopy.

RESULTS

A total of 104 actinomycetes were isolated and screened for antimicrobial activity; 21 strains were active against Staphylococcus aureus, Escherichia coli and Candida albicans. The strain E65 showed a high in vitro activity against S. aureus and C. albicans and a good antifungal activity against a clinical C. albicans strain resistant to 5-fluorocytosine. Its 16S rRNA sequence shared 99% similarity with the Streptomyces yatensis type strain within the Streptomyces violaceusniger subclade of the Streptomyces hygroscopicus clade. It produced a non-polyenic antifungal, the IR spectrum of the antifungal extract corresponded to none of the antimicrobials compounds known to be produced by actinomycete of the S. hygroscopicus clade.

CONCLUSION

The wetlands of El Kala, Algeria are a potential source of bioactive actinomycete that deserves to be explored and exploited. The Streptomyces yatensis E65 strain isolated from Mellah Lake brackish water produces a remarkable antifungal compound which original non-polyenic structure warrants further characterization.

In-vitro antimicrobial, antibiofilm, cytotoxic, antifeedant and larvicidal properties of novel quinone isolated from Aegle marmelos (Linn.) Correa

Background

Plant metabolites have wide applications and have the potential to cure different diseases caused by microorganisms. The aim of the study was to evaluate the antimicrobial, antibiofilm, cytotoxic, antifeedant and larvicidal properties of novel quinine isolated from Aegle marmelos (Linn.) Correa.

Methods

A compound was obtained by eluting the crude extract, using varying concentrations of the solvents by the chromatographic purification. Broth micro dilution method was used to assess the antimicrobial activity and anticancer study was evaluated using MTT assay. Larvicidal activity was studied using leaf disc no-choice method.

Results

Based on the IR, ¹³C NMR and ¹H NMR spectral data, the compounds were identified as quinone related antibiotic. It exhibited significant activity against Gram positive and Gram negative bacteria. The lowest Minimum Inhibitory Concentration (MIC) of the compound against Bacillus subtilis and Staphylococcus aureus was 100 and 75 μg mL⁻¹ respectively. Against Escherichia coli and Pseudomonas aeruginosa it exhibited MIC value of 25 μg mL⁻¹. The MIC of the compound against Aspergillus niger, A. clavatus, Penicillium roqueforti was 20 μg mL⁻¹ and that against Fusarium oxysporum (20 μg mL⁻¹), A. oryzae (40 μg mL⁻¹), and Candida albicans (60 μg mL⁻¹), respectively. It showed effective antibiofilm activity against E. coli, S. typhii and P. aeroginosa at 8 μg mL⁻¹ and did not exhibit considerable cytotoxic activity against Vero and HEP2 cell lines. Additionally, the compound documented significant antifeedant and larvicidal activities against Helicoverpa armigera and Spodoptera litura at 125, 250, 500 and 1000 ppm concentrations.

Conclusion

The results concluded that the compound can be evaluated further in industrial applications and also an agent to prepare botanical new pesticide formulations.

A New Pyrrolosesquiterpene from the Terrestrial Streptomyces sp. Hd7-21

One new pyrrolosesquiterpene 1 was isolated from cultures of the soil actinomycete Streptomyces sp. Hd7-21. Its structure was elucidated by extensive MS and 1D and 2D NMR spectroscopic data analyses.

Structural elucidation and NMR assignments of two new pyrrolosesquiterpenes from Streptomyces sp. Hd7-21

Two new pyrrolosesquiterpenes were isolated from cultures of the soil actinomycete Streptomyces sp. Hd7-21. The structures of these compounds were elucidated by extensive spectroscopic analyses including MS and 1D and 2D NMR data. Their cytotoxic activity against a panel of human cancer cell lines were biologically evaluated.