Ramesh Subramani

Marine actinomycetes: an ongoing source of novel bioactive metabolites

Actinomycetes are virtually unlimited sources of novel compounds with many therapeutic applications and hold a prominent position due to their diversity and proven ability to produce novel bioactive compounds. There are more than 22,000 known microbial secondary metabolites, 70% of which are produced by actinomycetes, 20% from fungi, 7% from Bacillus spp. and 1-2% by other bacteria. Among the actinomycetes, streptomycetes group are considered economically important because out of the approximately more than 10,000 known antibiotics, 50-55% are produced by this genus. The ecological role of actinomycetes in the marine ecosystem is largely neglected and various assumptions meant there was little incentive to isolate marine strains for search and discovery of new drugs. The search for and discovery of rare and new actinomycetes is of significant interest to drug discovery due to a growing need for the development of new and potent therapeutic agents. Modern molecular technologies are adding strength to the target-directed search for detection and isolation of bioactive actinomycetes, and continued development of improved cultivation methods and molecular technologies for accessing the marine environment promises to provide access to this significant new source of chemical diversity with novel/rare actinomycetes including new species of previously reported actinomycetes.

Cytotoxic and antibacterial substances against multi-drug resistant pathogens from marine sponge symbiont: Citrinin, a secondary metabolite of Penicillium sp.

OBJECTIVE To Isolate, purify, characterize, and evaluate the bioactive compounds from the sponge-derived fungus Penicillium sp. FF001 and to elucidate its structure. METHODS The fungal strain FF001 with an interesting bioactivity profile was isolated from a marine Fijian sponge Melophlus sp. Based on conidiophores aggregation, conidia development and mycelia morphological characteristics, the isolate FF001 was classically identified as a Penicillium sp. The bioactive compound was identified using various spectral analysis of UV, high resolution electrospray ionization mass spectra, 1H and 13C NMR spectral data. Further minimum inhibitory concentrations (MICs) assay and brine shrimp cytotoxicity assay were also carried out to evaluate the biological properties of the purified compound. RESULTS Bioassay guided fractionation of the EtOAc extract of a static culture of this Penicillium sp. by different chromatographic methods led the isolation of an antibacterial, anticryptococcal and cytotoxic active compound, which was identified as citrinin (1). Further, citrinin (1) is reported for its potent antibacterial activity against methicillin-resistant Staphylococcus aureus (S. aureus), rifampicin-resistant S. aureus, wild type S. aureus and vancomycin-resistant Enterococcus faecium showed MICs of 3.90, 0.97, 1.95 and 7.81 µg/mL, respectively. Further citrinin (1) displayed significant activity against the pathogenic yeast Cryptococcus neoformans (MIC 3.90 µg/mL), and exhibited cytotoxicity against brine shrimp larvae LD50 of 96 µg/mL. CONCLUSIONS Citrinin (1) is reported from sponge associated Penicillium sp. from this study and for its strong antibacterial activity against multi-drug resistant human pathogens including cytotoxicity against brine shrimp larvae, which indicated that sponge associated Penicillium spp. are promising sources of natural bioactive metabolites.

Aurantoside K, a New Antifungal Tetramic Acid Glycoside from a Fijian Marine Sponge of the Genus Melophlus

A new tetramic acid glycoside, aurantoside K, was isolated from a marine sponge belonging to the genus Melophlus. The structure of the compound was elucidated on the basis of spectroscopic analysis (1H NMR, 1H–1H COSY, HSQC, and HMBC, as well as high-resolution ESILCMS). Aurantoside K did not show any significant activity in antimalarial, antibacterial, or HCT-116 cytotoxicity assays, but exhibited a wide spectrum of antifungal activity against wild type Candida albicans, amphotericin-resistant C. albicans, Cryptococcus neoformans, Aspergillus niger, Penicillium sp., Rhizopus sporangia and Sordaria sp.

A novel antibacterial and antifungal phenolic compound from the endophytic fungus Pestalotiopsis mangiferae

A novel phenolic compound, 4-(2,4,7-trioxa-bicyclo[4.1.0]heptan-3-yl) phenol (1), was isolated from Pestalotiopsis mangiferae, an endophytic fungus associated with Mangifera indica Linn. The structure of the compound was elucidated on the basis of comprehensive spectral analysis (UV, IR, 1H-, 13C- and 2D-NMR, as well as HRESI–MS). Compound (1) shows potent antibacterial and antifungal activity against Bacillus subtilis, Klebsiella pneumoniae, Escherichia coli, Micrococcus luteus, Pseudomonas aeruginosa and Candida albicans. The transmission electron microscope study for the mode of inhibition of compound (1) on bacterial pathogens revealed the destruction of bacterial cells by cytoplasm agglutination with the formation of pores in cell wall membranes.

Plant-derived antimicrobials to fight against multi-drug-resistant human pathogens

Antibiotic resistance is becoming a pivotal concern for public health that has accelerated the search for new antimicrobial molecules from nature. Numbers of human pathogens have inevitably evolved to become resistant to various currently available drugs causing considerable mortality and morbidity worldwide. It is apparent that novel antibiotics are urgently warranted to combat these life-threatening pathogens. In recent years, there have been an increasing number of studies to discover new bioactive compounds from plant origin with the hope to control antibiotic-resistant bacteria. This review attempts to focus and record the plant-derived compounds and plant extracts against multi-drug-resistant (MDR) pathogens including methicillin-resistant Staphylococcus aureus (MRSA), MDR-Mycobacterium tuberculosis and malarial parasites Plasmodium spp. reported between 2005 and 2015. During this period, a total of 110 purified compounds and 60 plant extracts were obtained from 112 different plants. The plants reviewed in this study belong to 70 different families reported from 36 countries around the world. The present review also discusses the drug resistance in bacteria and emphasizes the urge for new drugs.

Three bioactive sesquiterpene quinones from the Fijian marine sponge of the genus Hippospongia

A sesquiterpenoid quinone, epi-ilimaquinone (1), and two sesquiterpene amino quinones, smenospongine (2) and glycinylilimaquinone (3), were isolated from the Fijian marine sponge Hippospongia sp. The structures of these compounds were determined by spectroscopic analysis. Compounds 1 and 3 were reported for the first time in this study from the sponge of the genus Hippospongia. Compound 1 displayed potent cytotoxic activity and showed antibacterial activity against methicillin-resistant Staphylococcus aureus, wild type S. aureus and vancomycin-resistant Enterococcus faecium and displayed antifungal activity against amphotericin-resistant Candida albicans while compounds 2 and 3 showed moderate cytotoxic activity. However, compound 1 did not show appreciable antifungal activity against wild type C. albicans, Cryptococcus neoformans, Aspergillus niger, Penicillium sp., Rhizopus sporangia or Sordaria sp.

Fungal 7- epi -10-deacetyltaxol produced by an endophytic Pestalotiopsis microspora induces apoptosis in human hepatocellular carcinoma cell line (HepG2)

BackgroundPaclitaxel (taxol) is a potent anticancer drug that is used in the treatment of a wide variety of cancerous. In the present study, we identified a taxol derivative named 7-epi-10-deacetyltaxol (EDT) from the culture of an endophytic fungus Pestalotiopsis microspora isolated from the bark of Taxodium mucronatum. This study was carried out to investigate the effects of fungal EDT on cell proliferation, the induction of apoptosis and the molecular mechanisms of apoptosis in human hepatoma HepG2 cells in vitro.MethodsThe endophytic fungus was identified by traditional and molecular taxonomical characterization and the fungal EDT was purified using column chromatography and confirmed by various spectroscopic and chromatographic comparisons with authentic paclitaxel. We studied the in vitro effects of EDT on HepG2 cells for parameters such as cell cycle distribution, DNA fragmentation, reactive oxygen species (ROS) generation and nuclear morphology. Further, western blot analysis was used to evaluate Bcl-2-associated X protein (Bax), B-cell lymphoma 2 (Bcl-2), p38-mitogen activated protein kinase (MAPK) and poly [ADP-ribose] polymerase (PARP) expression.ResultsWe demonstrate that the fungal EDT exhibited significant in vitro cytotoxicity in HepG2 cells. We investigated cytotoxicity mechanism of EDT in HepG2 cells. The results showed nuclear condensation and DNA fragmentation were observed in cells treated with fungal EDT. Besides, the fungal EDT arrested HepG2 cells at G2/M phase of cell cycle. Furthermore, fungal EDT induced apoptosis in HepG2 cells in a dose-dependent manner associated with ROS generation and increased Bax/Bcl-2 ratio, p38 MAPKs and PARP cleavage.ConclusionsOur data show that EDT induced apoptotic cell death in HepG2 cells occurs through intrinsic pathway by generation of ROS mediated and activation of MAPK pathway. This is the first report for 7-epi-10-deacetyltaxol (EDT) isolated from a microbial source.

Production and purification of a bioactive substance against multi-drug resistant human pathogens from the marine-sponge-derived Salinispora sp.

ABSTRACT Objective To isolate, purify, characterize, elucidate structure and evaluate bioactive compounds from the sponge-derived Salinispora sp. FS-0034. Methods The symbiotic actinomycete strain FS-0034 with an interesting bioactivity profile was isolated from the Fijian marine sponge Theonella sp. Based on colony morphology and obligatory requirement of seawater for growth, and mycelia morphological characteristics the isolate FS-0034 was identified as a Salinispora sp. The bioactive compound was identified by using various spectral analysis of ultraviolet, high resolution electrospray ionization mass spectroscopy, 1 H nuclear magnetic resonance, correlated spectroscopy and heteronuclear multiple bond coherence spectral data. A minimum inhibitory concentration assay were performed to evaluate the biological properties of the pure compound against multi-drug resistant pathogens. Results Bioassay guided fractionation of the ethyl acetate extract of the culture of Salinispora sp. FS-0034 by different chromatographic methods yielded the isolation of an antibacterial compound, which was identified as rifamycin W (compound 1). Rifamycin W was reported for its potent antibacterial activity against methicillin-resistant Staphylococcus aureus , wild type Staphylococcus aureus and vancomycin-resistant Enterococcus faecium and displayed minimum inhibitory concentrations of 15.62, 7.80 and 250.00 μg/mL, respectively. Conclusions The present study reported the rifamycin W from sponge-associated Salinispora sp. and it exhibited appreciable antibacterial activity against multi-drug resistant human pathogens which indicated that sponge-associated Actinobacteria are significant sources of bioactive metabolites.

Marinocyanins, cytotoxic bromo-phenazinone meroterpenoids from a marine bacterium from the streptomycete clade MAR4

Six cytotoxic and antimicrobial metabolites of a new bromo-phenazinone class, the marinocyanins A-F (1-6), were isolated together with the known bacterial metabolites 2-bromo-1-hydroxyphenazine (7), lavanducyanin (8, WS-9659A) and its chlorinated analog WS-9659B (9). These metabolites were purified by bioassay-guided fractionation of the extracts of our MAR4 marine actinomycete strains CNS-284 and CNY-960. The structures of the new compounds were determined by detailed spectroscopic methods and marinocyanin A (1) was confirmed by crystallographic methods. The marinocyanins represent the first bromo-phenazinones with an N-isoprenoid substituent in the skeleton. Marinocyanins A-F show strong to weak cytotoxicity against HCT-116 human colon carcinoma and possess modest antimicrobial activities against Staphylococcus aureus and amphotericin-resistant Candida albicans.