Isolation, characterization, and structural elucidation of 4-methoxyacetanilide from marine actinobacteria Streptomyces sp. SCA29 and evaluation of its enzyme inhibitory, antibacterial, and cytotoxic potential

Investigation of anti-microbial and cytotoxic potential of Streptomyces werraensis GRS9 derived from the sediments of river Ganga

The aim of the present work was to screen bacterial and actinomycetes strains from the sediments of river Ganga (India) as a promising source of anti-microbial and anti-cancer agents along with spectroscopic and chromatographic identification of bio-active compounds. The strain GRS9 exhibited broad-spectrum bio-activity against all the 15-test organisms incorporated in our study with minimum inhibitory concentrations (MICs) ranging from 16 µg/ml against Staphylococcus aureus MTCC3160 to 500 μg/ml for Escherichia coli (MTCC118). The cytotoxic profile of ethyl acetate extract was also evaluated against Human Colon Cancer Cell Line (HCT116) by Neutral Red Uptake (NRU) assay, followed by in silico study to determine its pre-qualification for drug suitability. The results indicated that Streptomyces werraensis GRS9 extract possessed anti-cancer properties (IC50 = 22.95 µg/ml) and found suitable for further drug development as reflected in Absorption, Distribution, Metabolism and Excretion (ADME) prediction having no violation of Lipinski's rule of five. Bioactive compounds associated with GRS9 were identified by Gas Chromatography Mass Spectroscopy (GC-MS) and Fourier Transform Infrared Spectroscopy (FTIR), revealing 29 compounds along with 10 major compounds identified via National Institute of Standards and Technology (NIST) /Wiley library. These compounds include N-(4-methyl-1-Piperzinyl)-1-Napthamide (a compound of immense pharmacological potential especially in oncology) along with anti-microbials i.e. Dodecanamide and 1,2-Benzenedicarboxylic acid, Diethyl ester. The findings revealed our sediment isolate Streptomyces werraensis GRS9 to be a suitable candidate for the isolation and purification of bio-active compounds that may act as a source of anti-microbial and anti-cancer agents.

Actinomycetota isolated from the sponge Hymeniacidon perlevis as a source of novel compounds with pharmacological applications: diversity, bioactivity screening, and metabolomic analysis

AIMS

To combat health conditions, such as multi-resistant bacterial infections, cancer, and metabolic diseases, new drugs need to be urgently found and, in this respect, marine Actinomycetota have a high potential to produce secondary metabolites with pharmacological importance. We aimed to study the cultivable Actinomycetota community associated with a marine sponge from the Portuguese coast, Hymeniacidon perlevis, and investigate the potential of the retrieved isolates to produce compounds with antimicrobial, anticancer and anti-obesity properties.

METHODS AND RESULTS

The analysis of the 16S rRNA gene revealed 79 Actinomycetota isolates affiliated with 12 genera-Brachybacterium, Dietzia, Glutamicibacter, Gordonia, Micrococcus, Micromonospora, Nocardia, Nocardiopsis, Paenoartrhobacter, Rhodococcus, Streptomyces, and Tsukamurella, most of which affiliated with the genus Streptomyces. The screening of antimicrobial activity revealed 13 strains, all belonging to the Streptomyces genus, capable of inhibiting the growth of Candida albicans, Bacillus subtilis, or Staphylococcus aureus. Forty-three extracts exhibited cytotoxic activity against at least one tested cell line (HepG2, HCT-116, and hCMEC-D3). Three extracts that were active against the two cancer cell lines tested, did not reduce the viability of the non-cancer endothelial cell line, hCMEC-D3. One Gordonia strain exhibited anti-obesity activity, revealed by its ability to reduce the neutral lipids in zebrafish larvae. Mass spectrometry-based dereplication analysis of active extracts identified several compounds associated with known Actinomycetota natural products. Nonetheless, five clusters contained metabolites that did not match any annotated natural products, suggesting they may represent new bioactive molecules.

CONCLUSIONS

This work contributed to increase the knowledge on the diversity and bioactive potential of Actinomycetota associated with H. perlevis.

Biocontrol Potential of Rhizospheric Bacillus Strains Against Sclerotinia minor Jagger Causing Lettuce Drop

Phytopathogenic Sclerotinia minor Jagger causes lettuce drop, a destructive soil-borne disease. As potential biocontrol agents for this disease, 2 of 31 bacterial strains isolated from soil samples from fields containing S. minor Jagger were identified using in vitro antagonistic assays against S. minor Jagger. Bioactivity experiments showed that Bac20 had higher inhibitory activity against S. minor Jagger than Bac45. Based on 16S rRNA sequences and phylogenetic analysis of a combination of sequences from gyrA, rpoB, purH, polC, and groEL, Bac20 and Bac45 were identified as Bacillus velezensis and Bacillus subtilis, respectively. Lipopeptide compounds produced by each strain were identified using matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) analysis. Both strains produced three types of lipopeptides, namely surfactins, iturins, and fengycins, whereas Bac20 showed the strongest intensity in its production of iturins, more than that of Bac45. Bac20 inhibited oxalic acid formation in early-stage lettuce leaves infected with S. minor Jagger, delaying pathogen infestation. Greenhouse experiments for controlling lettuce drop demonstrated that inoculation with Bac20 controlled lettuce drop by 71.7%. In conclusion, this study revealed that B. velezensis Bac20 has high potential for use as a biocontrol agent for controlling the lettuce drop caused by S. minor Jagger.

Synthesis and antimycotic activity of new derivatives of imidazo[1,2-a]pyrimidines

The heterocyclic core of imidazo[1,2-a]pyrimidine was formed in satisfactory yields as a result of the interaction of the readily available 2-aminoimidazole with N-substituted maleimides or N-arylitaconimides. The mechanism of the studied processes was postulated basing on experimental data, HPLC-MS analysis of reaction mixtures, and quantum chemical calculations. Molecular docking results of the obtained imidazo[1,2-a]pyrimidines, when compared with voriconazole, a drug already in clinical use, suggest that they may possess antifungal activity against Candida albicans.

Unlocking the therapeutic potential of bioactive exopolysaccharide produced by marine actinobacterium Streptomyces vinaceusdrappus AMG31: A novel approach to drug development

Acidic exopolysaccharide (EPS) was produced by a marine actinobacterium Streptomyces vinaceusdrappus strain AMG31 with the highest yield of 10.6 g/l. The synthesized EPS has an average molecular weight of 5.1 × 104 g/mol and contains arabinose, glucose, galacturonic acid (0.5:2:2 M ratio), with 39.77 % uronic acid residues and 18.8 % sulfate detected. EPS exhibited antioxidant activities with 93.8 % DPPH radical scavenging and 344.7 μg/mg total antioxidant capacity. It displayed anti-inflammatory effects by inhibiting 5-LOX and COX-2. Regarding the cytotoxic activity, the IC50 values are 301.6 ± 11.8, 260.8 ± 12.2, 29.4 ± 13.5, 351.3 ± 11.2, 254.1 ± 9.8, and 266.5 ± 10.4 μg/ml for PC-3, HEP-2, MCF-7, HCT-116, A-549, HepG-2 respectively, which indicate that the produced EPS does not have strong cytotoxic activities. Moreover, the EPS showed anti-Alzheimer activity via inhibition of the Butyrylcholinesterase enzyme, with the highest percentage of 84.5 % at 100 μg/ml. Interestingly, the EPS showed superior anti-obesity activity by inhibiting lipase enzyme with a rate of 95.3 % compared to orlistat as a positive control (96.8 %) at a concentration of 1000 μg/ml. Additionally, the produced EPS displayed the highest anti-diabetic properties by inhibiting α-amylase (IC50 31.49 μg/ml) and α-glucosidase (IC50 6.48 μg/ml), suggesting antidiabetic potential analogous to acarbose. EPS exhibited promising antibacterial and antibiofilm activity against a wide range of Gram-positive and Gram-negative pathogenic bacteria.

Metabolites extracted from microorganisms as potential inhibitors of glycosidases (α-glucosidase and α-amylase): A review

α-Glucosidase and α-amylase are the two main glycosidases that participate in the metabolism of carbohydrates. Inhibitors of these two enzymes are considered an important medical treatment for carbohydrate uptake disorders, such as diabetes and obesity. Microbes are an important source of constituents that have the potential to inhibit glycosidases and can be used as sources of new drugs and dietary supplements. For example, the α-glucosidase inhibitor acarbose, isolated from Actinoplanes sp., has played an important role in adequately controlling type 2 diabetes, but this class of marketed drugs has many drawbacks, such as poor compliance with treatment and expense. This demonstrates the need for new microorganism-derived resources, as well as novel classes of drugs with better compliance, socioeconomic benefits, and safety. This review introduces the literature on microbial sources of α-glucosidase and α-amylase inhibitors, with a focus on endophytes and marine microorganisms, over the most recent 5 years. This paper also reviews the application of glycosidase inhibitors as drugs and dietary supplements. These studies will contribute to the future development of new microorganism-derived glycosidase inhibitors.

Mutactimycin AP, a New Mutactimycin Isolated from an Actinobacteria from the Atacama Desert

Bacteria belonging to the phylum Actinobacteria are a very good source of antibiotics, and indeed dominate the current clinical antibiotic space. This paper reports Mutactimycin AP, a new compound belonging to an anthracycline-type family of antibiotics, isolated from a Saccharothrix sp. This actinobacterial strain was isolated from the rhizosphere of lupine plants growing in the extreme hyper-arid Atacama Desert. Structural characterization was carried out using electrospray ionization-mass spectrometry (ESI-MS) and NMR spectroscopy in combination with molecular modelling. The compound was tested against the ESKAPE pathogens, where it showed activity against MRSA and five strains associated with bovine mastitis, where it showed activity against Enterococcus pseudoavium and Staphylycoccus Aureus subsp. Aureus.

Marine Actinobacteria a New Source of Antibacterial Metabolites to Treat Acne Vulgaris Disease—A Systematic Literature Review

Acne vulgaris is a multifactorial disease that remains under-explored; up to date it is known that the bacterium Cutibacterium acnes is involved in the disease occurrence, also associated with a microbial dysbiosis. Antibiotics have become a mainstay treatment generating the emergence of antibiotic-resistant bacteria. In addition, there are some reported side effects of alternative treatments, which indicate the need to investigate a different therapeutic approach. Natural products continue to be an excellent option, especially those extracted from actinobacteria, which represent a prominent source of metabolites with a wide range of biological activities, particularly the marine actinobacteria, which have been less studied than their terrestrial counterparts. Therefore, this systematic review aimed to identify and evaluate the potential anti-infective activity of metabolites isolated from marine actinobacteria strains against bacteria related to the development of acne vulgaris disease. It was found that there is a variety of compounds with anti-infective activity against Staphylococcus aureus and Staphylococcus epidermidis, bacteria closely related to acne vulgaris development; nevertheless, there is no report of a compound with antibacterial activity or quorum-sensing inhibition toward C. acnes, which is a surprising result. Since two of the most widely used antibiotics for the treatment of acne targeting C. acnes were obtained from actinobacteria of the genus Streptomyces, this demonstrates a great opportunity to pursue further studies in this field, considering the potential of marine actinobacteria to produce new anti-infective compounds.

Natural Products from Actinobacteria as a Potential Source of New Therapies Against Colorectal Cancer: A Review

Colorectal cancer (CRC) is a common, and deadly disease. Despite the improved knowledge on CRC heterogeneity and advances in the medical sciences, there is still an urgent need to cope with the challenges and side effects of common treatments for the disease. Natural products (NPs) have always been of interest for the development of new medicines. Actinobacteria are known to be prolific producers of a wide range of bioactive NPs, and scientific evidence highlights their important protective role against CRC. This review is a holistic picture on actinobacter-derived cytotoxic compounds against CRC that provides a good perspective for drug development and design in near future. This review also describes the chemical structure of 232 NPs presenting anti-CRC activity with the being majority of quinones, lactones, alkaloids, peptides, and glycosides. The study reveals that most of these NPs are derived from marine actinobacteria followed by terrestrial and endophytic actinobacteria, respectively. They are predominantly produced by Streptomyces, Micromonospors, Saliniospors and Actinomadura, respectively, in which Streptomyces, as the predominant contributor generating over 76% of compounds exclusively. Besides it provides a valuable snapshot of the chemical structure-activity relationship of compounds, highlighting the presence or absence of some specific atoms and chemical units in the structure of compounds can greatly influence their biological activities. To the best of our knowledge, this is the first comprehensive review on natural actinobacterial compounds affecting different types of CRC. Our study reveals that the high diversity of actinobacterial strains and their NPs derivatives, described here provides a new perspective and direction for the production of new anti-CRC drugs and paves the way to innovation for drugs discovery in the future. The knowledge obtain from this review can help us to understand the pivotal application of actinobacteria in future drugs development.

Streptomyces sp. 1S1 isolated from Southern coast of the Red Sea as a renewable natural resource of several bioactive compounds

Red Sea represents one of the most remarkable marine ecosystems. However, it is also one of the world's least explored areas of marine biodiversity. The aims of this investigation were therefore, to isolate marine microorganisms from the seashore sediments and water in shallow region from west Yemen coast, to assess their antimicrobial potential, to identify the highly active isolate, and to purify and identify the bioactive compounds from it. In this regard, twenty-five bacterial strains have been isolated from twenty samples and tested for their antimicrobial ability against some pathogenic bacteria and yeast by using the agar disk diffusion and agar well diffusion assay. Out of the total 25 marine actinomycetes isolates only 13 exhibited interesting antimicrobial activity. The morphological, biochemical, and phylogenetic characteristics of the potential isolate 1S1 were compatible with their classification in the genus Streptomyces. The 16S rRNA gene sequences have shown that the isolate 1S1 clustered with Streptomyces longisporoflavus. The strain Streptomyces sp. 1S1 was cultivated and extracted with ethyl acetate. The GC–MS study of the extract indicated the presence of certain fatty acyl compounds e.g., tetradecanoic acid, 9-octadecenoic acid, hexadecanoic acid, and 9,12,15-octadecatrienoic acid. Using chromatographic techniques, three compounds were isolated and by spectroscopic methods e.g., IR, MS and NMR structurally elucidated. The three compounds were identified as a triacylglyceride, 9-octadecenoic acid, and hexadecanoic acid. The study reinforces the evidence of the potential of Streptomyces sp and the ability to produce several antimicrobial compounds.

Diketopiperazine derivative from marine actinomycetes Nocardiopsis sp. SCA30 with antimicrobial activity against MRSA

Actinobacteria isolated from marine sources are a potential source of novel natural products. In this study, we report isolation, biological activity and characterization of secondary metabolites from strain Nocardiopsis sp. SCA30, isolated from marine sediments of Havelock Islands, Andaman and Nicobar, India. The ethyl acetate extracts of the isolate on screening for biological activity demonstrated antibacterial potency and antiproliferative activity. The extracts showed anticancer activity in a panel of cell lines, including HCT 15, HT 29, MCF 7 and MDA-MB 468, at concentrations ranging from 62.5 to 1000 µg/ml. A dose-dependent reduction in cell viability was observed in all the tested cell lines. The extract at 15 µg/ml and 30 µg/ml inhibited growth of methicillin-resistant Staphylococcus aureus ATCC NR-46071 and NR-46171 with MIC's of 15.62 and 7.81 µg/ml, respectively. LC-MS and NMR studies revealed that the antibacterial and anticancer compound isolated from Nocardiopsis sp. SCA30 is 1-acetyl-4-4(hydroxyphenyl)piperazine.

Antimicrobial resistance in biofilms: Exploring marine actinobacteria as a potential source of antibiotics and biofilm inhibitors

Antimicrobial resistance (AMR) is one of the serious global public health threats that require immediate action. With the emergence of new resistance mechanisms in infection-causing microorganisms such as bacteria, fungi, and viruses, AMR threatens the effective prevention and treatment of diseases caused by them. This has resulted in prolonged illness, disability, and death. It has been predicted that AMR will lead to over ten million deaths by 2050. The rapid spread of multidrug-resistant bacteria is also causing old antibiotics to become ineffective. Among the diverse factors contributing to AMR, intrinsic biofilm development has been highlighted as an essential contributing facet. Moreover, biofilm-derived antibiotic tolerance leads to serious recurrent chronic infections. Therefore, the discovery of novel bioactive molecules is a potential solution that can help combat AMR. To achieve this, sustained mining of novel antimicrobial leads from actinobacteria, particularly marine actinobacteria, can be a promising strategy. Given their vast diversity and different habitats, the extraordinary capacity of actinobacteria can be tapped to synthesize new antibiotics or bioactive molecules for biofilm inhibition. Advanced screening strategies and novel approaches in the field of modern biochemical and molecular biology can be used to detect such new compounds. In view of this, the present review focuses on understanding some of the recent strategies to inhibit biofilm formation and explores the potential role of marine actinobacteria as sources of novel antibiotics and biofilm inhibitor molecules.

A Novel 4H-Chromen-4-One Derivative from Marine Streptomyces ovatisporus S4702T as Potential Antibacterial and Anti-Cancer Agent

BACKGROUND

Marine actinomycetes are among indispensable sources of natural bioactive compounds with unique antimicrobial and anti-cancer activities.

OBJECTIVE

Herein, it was aimed to elucidate bioactive potential of a marine-derived Streptomyces ovatisporus S4702T, isolated previously.

METHODS

Streptomyces ovatisporus S4702T was cultured in N-Z Amine broth and extraction was carried out using different organic solvents. Bioassay guided purification was followed by chemical characterization using NMR and LC-MS/MS. The compound was then evaluated for its antibacterial, antioxidant and cytotoxic activities.

RESULTS

Etyl acetate extracts gave the highest antibacterial activity and chemical characterization of this extract indicated the formula as C15H29O5N3 and the corresponding possible molecular structure as 4H-chromen-4-one derivative. It was found highly potent against Bacillus subtilis ATCC 6633 (MIC: 0.25 µg ml-1) and Micrococcus luteus ATCC 9341 (MBC: 0.5 µg ml-1). It has no remarkable antioxidant activity, but higher EC50 value and less cytotoxicity against normal cells. The EC50 values of this chromen derivative were found as 9.68 µg ml-1 for human colon carcinoma, 9.93 µg ml-1 for human prostate adenocarcinoma and 25.5 µg ml-1 for human embryonic kidney cells.

CONCLUSION

Overall, the presented 4H-chromen-4-one derivative is a remarkable bioactive compound with potent antibacterial and cytotoxic activity. With its high bioactive potential, it is proposed as a good candidate in medicine.

Marine natural products

This review covers the literature published in 2019 for marine natural products (MNPs), with 719 citations (701 for the period January to December 2019) referring to compounds isolated from marine microorganisms and phytoplankton, green, brown and red algae, sponges, cnidarians, bryozoans, molluscs, tunicates, echinoderms, mangroves and other intertidal plants and microorganisms. The emphasis is on new compounds (1490 in 440 papers for 2019), together with the relevant biological activities, source organisms and country of origin. Pertinent reviews, biosynthetic studies, first syntheses, and syntheses that led to the revision of structures or stereochemistries, have been included. Methods used to study marine fungi and their chemical diversity have also been discussed.

Antibiotics Development and the Potentials of Marine-Derived Compounds to Stem the Tide of Multidrug-Resistant Pathogenic Bacteria, Fungi, and Protozoa

As the search for new antibiotics continues, the resistance to known antimicrobial compounds continues to increase. Many researchers around the world, in response to antibiotics resistance, have continued to search for new antimicrobial compounds in different ecological niches such as the marine environment. Marine habitats are one of the known and promising sources for bioactive compounds with antimicrobial potentials against currently drug-resistant strains of pathogenic microorganisms. For more than a decade, numerous antimicrobial compounds have been discovered from marine environments, with many more antimicrobials still being discovered every year. So far, only very few compounds are in preclinical and clinical trials. Research in marine natural products has resulted in the isolation and identification of numerous diverse and novel chemical compounds with potency against even drug-resistant pathogens. Some of these compounds, which mainly came from marine bacteria and fungi, have been classified into alkaloids, lactones, phenols, quinones, tannins, terpenes, glycosides, halogenated, polyketides, xanthones, macrocycles, peptides, and fatty acids. All these are geared towards discovering and isolating unique compounds with therapeutic potential, especially against multidrug-resistant pathogenic microorganisms. In this review, we tried to summarize published articles from 2015 to 2019 on antimicrobial compounds isolated from marine sources, including some of their chemical structures and tests performed against drug-resistant pathogens.

Isolation and characterization of bioactive compounds with antibacterial, antioxidant and enzyme inhibitory activities from marine-derived rare actinobacteria, Nocardiopsis sp. SCA21

A rare actinobacteria strain designated SCA21, producing bioactive metabolites was isolated from marine sediment of Havelock Island, Andaman and Nicobar Islands, India. Analysis of 16S rRNA sequences suggested that the strain SCA21 belonged to the genus Nocardiopsis. Chemical investigation of the fermentation broth led to the isolation of two pure bioactive compounds (1-2). Compound 1: 4-bromophenol, a bromophenol derivative; Compound 2: Bis (2-ethylhexyl) phthalate, a phthalate ester. The structure of compound 1 and 2 were elucidated by the detailed analysis of FT-IR, HR-ESI-MS, 1D and 2D NMR, along with literature data analysis. The isolated metabolites were evaluated for enzyme inhibition activity against α-glucosidase and α-amylase, free radical scavenging activity against DPPH and ABTS radicals, metal chelating and antibacterial activity against clinical pathogens. 1 and 2 exhibited remarkable enzyme inhibitory activities against α-glucosidase. However, Compound 2 was found less active against α-amylase. They showed significant free radical scavenging activity against DPPH and ABTS radicals. In addition, except the strain Salmonella typhi ATCC 25241 and Listeria cytogens ATCC 13932, 1 and 2 showed broad spectrum inhibitory activity against MRSA ATCC NR-46171, MRSA ATCC-46071, Klebsiella pneumonia ATCC 13883, Bacillus subtilis ATCC 6633, Staphylococcus aureus ATCC 12600. In conclusion, to best of our knowledge these findings are the first report of isolation of 4-bromophenol and Bis (2-ethylhexyl) phthalate from genus Nocardiopsis, thus suggesting that rare actinomycetes are promising source of therapeutically important bioactive metabolites.