Didehydroroflamycoin pentaene macrolide family from Streptomyces durmitorensis MS405T : production optimization and antimicrobial activity

Susceptibility pattern of methicillin resistance Staphylococcus aureus (MRSA) by flow cytometry analysis and characterization of novel lead drug molecule from Streptomyces species

BACKGROUND

Actinomycetes particularly, Streptomyces species are producing wide variety of natural products with potential bioactivities. The microbial-derived metabolites hold a strong position to combat emerging and re-emerging antimicrobial drug-resistant pathogens.

OBJECTIVES

A diverse group of actinomycetes strains were isolated from unexplored regions of mangrove sediment. Further, a polyphasic approach based on 16S rRNA gene sequence analysis and to evaluate their antibacterial potential against a panel of bacterial pathogens and methicillin resistance Staphylococcus aureus (MRSA).

METHODS

The mangrove sediment samples were serially diluted with sterile water and plated on inorganic starch agar medium. A total of 20 isolates were pure cultured and 16S rRNA gene sequences were deposited in the public nucleotide databases (GenBank, NCBI). All the isolates were screened for the antibacterial activity by agar overlay method. Further, the susceptibility pattern of MRSA by flow cytometry and fluorescence microscopy was analysed.

RESULTS

These twenty different isolates were grouped under nine major clad and they shared 95-99% sequence identity to the 16S rRNA gene sequences of the genus Streptomyces in the public nucleotide databases. Among these strains, the isolates namely JRG-02, JRG-03, JRG-04, JRG-10 and JRG-12 exhibited a broad-spectrum antibacterial activity against Methicillin-resistant Staphylococcus aureus(MRSA) and Gram negative bacteria Klebsiella pneumoniae MTCC109. Furthermore, we have characterized the antibacterial compound production and its properties from the isolate JRG-02, a potential drug candidate. The culture conditions and various nutrient components of strain Streptomyces sp. JRG-02 were optimized for enhanced antibiotics production of the isolate. The FT-IR and LCMS spectrum analysis envisaged the chemical nature of the substance. The effect of antibacterial compound on the viability of MRSA was alone examined by flow cytometry (FACS) and fluorescence microscopy analysis.

CONCLUSIONS

The present study clearly shows that the survival of diverse inhabitants of Streptomyces in the mangrove sediments. Hence, the mangrove sediment inhabiting strain Streptomyces sp. JRG-02 has potential pharmaceutical activity and genetic diversity.

Streptomyces sp. BV410 isolate from chamomile rhizosphere soil efficiently produces staurosporine with antifungal and antiangiogenic properties

Applying a bioactivity‐guided isolation approach, staurosporine was separated and identified as the active principle in the culture extract of the new isolate Streptomyces sp. BV410 collected from the chamomile rhizosphere. The biotechnological production of staurosporine by strain BV410 was optimized to yield 56 mg/L after 14 days of incubation in soy flour–glucose–starch–mannitol‐based fermentation medium (JS). The addition of FeSO₄ significantly improved the staurosporine yield by 30%, while the addition of ZnSO₄ significantly reduced staurosporine yield by 62% in comparison with the starting conditions. Although staurosporine was first isolated in 1977 from Lentzea albida (now Streptomyces staurosporeus) and its potent kinase inhibitory effect has been established, here, the biological activity of this natural product was assessed in depth in vivo using a selection of transgenic zebrafish (Danio rerio) models, including Tg(fli1:EGFP) with green fluorescent protein‐labeled endothelial cells allowing visualization and monitoring of blood vessels. This confirmed a remarkable antiangiogenic activity of the compound at doses of 1 ng/ml (2.14 nmol/L) which is below doses inducing toxic effects (45 ng/ml; 75 nmol/L). A new, efficient producing strain of commercially significant staurosporine has been described along with optimized fermentation conditions, which may lead to optimization of the staurosporine scaffold and its wider applicability.

Disease control efficacy of 32,33-didehydroroflamycoin produced by Streptomyces rectiviolaceus strain DY46 against gray mold of tomato fruit

Despite the efficacy of synthetic fungicides in controlling postharvest diseases, public concerns regarding chemical residues in food and an increase in drug-resistant strains of pathogens have led to a need for new agents to control postharvest diseases. The current study was performed to find control agents of microbial origin that are effective on gray mold of tomato fruits. We recently isolated Streptomyces rectiviolaceus DY46, which has antagonistic activity against various plant pathogenic fungi. The incidence of gray mold of tomato fruits was markedly reduced by 80.0% in tomatoes treated with the cell extract of Streptomyces rectiviolaceus DY46 compared with the control tomatoes. The active ingredient was purified from the cell extract of DY46 and identified to be 32,33-didehydroroflamycoin (DDHR). DDHR displayed MICs (minimal inhibitory concentrations) against the mycelial growth of various plant pathogenic fungi at concentrations of 8–64 mg L⁻¹. The incidence of gray mold in tomato fruits inoculated with conidial suspension (10⁴ conidia mL⁻¹) of Botrytis cinerea was markedly reduced by 88.9% in tomatoes treated with DDHR (100 mg L⁻¹) compared with the control. The DDHR residue in tomato fruit was significantly diminished 2 d after treatment. These results show that DDHR would be relatively safe for use as a postharvest fungicide.

Antifungal potential of bacterial rhizosphere isolates associated with three ethno-medicinal plants (poppy, chamomile, and nettle)

The objective of the present study was to isolate Actinobacteria, preferably Streptomyces spp. from the rhizosphere soils of three ethno-medicinal plants collected in Serbia (Papaver rhoeas, Matricaria chamomilla, and Urtica dioica) and to screen their antifungal activity against Candida spp. Overall, 103 sporulating isolates were collected from rhizosphere soil samples and determined as Streptomyces spp. Two different media and two extraction procedures were used to facilitate identification of antifungals. Overall, 412 crude cell extracts were tested against Candida albicans using disk diffusion assays, with 42% (43/103) of the strains showing the ability to produce antifungal agents. Also, extracts inhibited growth of important human pathogens: Candida krusei, Candida parapsilosis, and Candida glabrata. Based on the established degree and range of antifungal activity, nine isolates, confirmed as streptomycetes by 16S rRNA sequencing, were selected for further testing. Their ability to inhibit Candida growth in liquid culture, to inhibit biofilm formation, and to disperse pre-formed biofilms was assessed with active concentrations from 8 to 250 μg/mL. High-performance liquid chromatographic profiles of extracts derived from selected strains were recorded, revealing moderate metabolic diversity. Our results proved that rhizosphere soil of ethno-medicinal plants is a prolific source of streptomycetes, producers of potentially new antifungal compounds.

Control of human and plant fungal pathogens using pentaene macrolide 32, 33-didehydroroflamycoin

AIMS

The aim of this study was to address the toxicity of recently described polyene macrolide 32, 33-didehydroroflamycoin (DDHR) on a wide range of fungal pathogens and its potential to control plant fungal diseases.

METHODS AND RESULTS

The antifungal activity of DDHR in vitro was examined against common human and plant pathogenic fungi using a broth microdilution assay and a disk diffusion assay. Minimum inhibitory concentrations ranged from 12·5 to 35 μg ml(-1) . A radial growth inhibition assay showed that DDHR inhibited mycelia growth, inducing mycelial necrosis and affecting sporulation. During the in vivo assay on apple fruits administration of DDHR 1 h before fungal inoculation inhibited spreading of the infection. Importantly, DDHR exhibited no phytotoxic effects on the model plant, Capsicum annum, verified by the plant growth rate and chlorophyll content.

CONCLUSIONS

DDHR inhibits growth of various plant pathogens in vitro with the strongest activity against Alternaria alternata, Colletotrichum acutatum and Penicillium expansum, and protects apple fruits from decay.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first report of the inhibitory effect of DDHR on important pathogenic fungal isolates. DDHR could be a good scaffold for developing new antifungal agents for fruit and vegetable protection.

Membrane activity of the pentaene macrolide didehydroroflamycoin in model lipid bilayers

Didehydroroflamycoin (DDHR), a recently isolated member of the polyene macrolide family, was shown to have antibacterial and antifungal activity. However, its mechanism of action has not been investigated. Antibiotics from this family are amphiphilic; thus, they have membrane activity, their biological action is localized in the membrane, and the membrane composition and physical properties facilitate the recognition of a particular compound by the target organism. In this work, we use model lipid membranes comprised of giant unilamellar vesicles (GUVs) for a systematic study of the action of DDHR. In parallel, experiments are conducted using filipin III and amphotericin B, other members of the family, and the behavior observed for DDHR is described in the context of that of these two heavily studied compounds. The study shows that DDHR disrupts membranes via two different mechanisms and that the involvement of these mechanisms depends on the presence of cholesterol. The leakage assays performed in GUVs and the conductance measurements using black lipid membranes (BLM) reveal that the pores that develop in the absence of cholesterol are transient and their size is dependent on the DDHR concentration. In contrast, cholesterol promotes the formation of more defined structures that are temporally stable.

Antimicrobial potential of phylogenetically unique actinomycete, Streptomyces sp. JRG-04 from marine origin

Due to the emergence of severe infectious diseases and thriving antibiotic resistance, there is a need to explore microbial-derived bioactive secondary metabolites from unexplored regions. Present study deals with a mangrove estuary derived strain of Streptomyces sp. with potent antimicrobial activity against various pathogens, including methicillin resistant Staphylococcus aureus. Bioactive compound was effective even at low MIC level, damages the membrane of methicillin resistant S. aureus and causes cell death, however it has no cytotoxic effect on H9C2 cells. 16S rRNA shared 99.5% sequence similarity to Streptomyces longispororuber. Optimum biomass and antimicrobial compound production were observed in production medium supplemented with 1.0% maltose and 0.5% yeast extract. The active compound purified from the chloroform extract of the cell-free supernatant was studied by FT-IR, 1H NMR, 13C NMR and LC ESI-MS and identified as aromatic polyketide. β-ketosynthase (KS) domain of the Streptomyces strain revealed 93.2% sequence similarity to the benzoisochromanequinone, an actinorhodin biosynthetic gene cluster of Streptomyces coelicolor A3(2). However, the region synthesizing the secondary metabolite produced by the S. longispororuber was not related to the KS domain of the strain, due to the phenomenon of horizontal gene transfer over the period of evolutionary process, thus generating metabolic compound diversity.

Synthesis of γ-nitroaldehydes containing quaternary carbon in the α-position using a 4-oxalocrotonate tautomerase whole-cell biocatalyst

Synthetically valuable quaternary carbon containing γ-nitroaldehydes were obtained from branched chain aldehydes and a range of α,β-unsaturated nitroalkenes by a whole-cell biocatalytic reaction using 4-oxalocrotonate tautomerase as catalyst.