Setomimycin as a potential molecule for COVID‑19 target: in silico approach and in vitro validation

Synergistic effect of kanamycin and amikacin with setomimycin on biofilm formation inhibition of Listeria monocytogenes

Listeria monocytogenes, a foodborne pathogen that causes listeriosis with high fatality rate, exhibits multidrug resistance (MDR) known to be progressively increasing. Alternative antibacterial strategies are in high demand for treating this well-known pathogen. Anti-biofilm and anti-virulence strategies are being explored as novel approaches to treat bacterial infections. In this study, one rare antibacterial named setomimycin was isolated from Streptomyces cyaneochromogenes, which showed potent antibacterial activity against L. monocytogenes. Next, the inhibition of biofilm formation and listeriolysin O (LLO) production against L. monocytogenes were investigated at sub-minimal inhibitory concentrations (sub-MICs) of setomimycin alone or combined with kanamycin and amikacin. Crystal violet staining confirmed that setomimycin combining with kanamycin or amikacin could dramatically reduce biofilm formation against L. monocytogenes at sub-MICs, which was further evaluated by scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM). In the meantime, sub-MICs of setomimycin could significantly suppress the secretion of LLO. Furthermore, the transcription of genes associated with biofilms and main virulence factors, such as LLO, flagellum, and metalloprotease, were suppressed by setomimycin at sub-MICs. Hence, the study provided a deep insight into setomimycin as an alternative antibacterial agent against L. monocytogenes.

Identification and taxonomy of Streptomyces justiciae strain RA-WS2: a novel setomimycin producing actinobacterium

The taxonomic position of novel bianthraquinone antibiotic producer Streptomyces strain RA-WS2, a soil isolate from Shivalik region of NW Himalayas, India, has been described. The isolate produces Setomimycin as a major secondary metabolite under defined submerged fermentation conditions. 16S rRNA partial gene sequencing of the isolate indicated its closest similarity (99.4%) with Streptomyces cyaneochromogenes, followed by Streptomyces aquilus. However, the morphological characteristics i.e. colony colour, mycelium and spore chain arrangement were found to be close to Streptomyces aquilus. Therefore, a polyphasic approach was used for taxonomic positioning of the isolate. The Whole genome based similarity with 88.4% dDDH value, 98.65% ANI and 96.99% AAI value indicated its closest identity with Streptomyces justiciae. The taxonomic characteristics such as white colony with smooth surface, cylindrical spores arranged in straight chain, diffusible melanin production, high salt tolerance, 16S rRNA gene sequencing and phylogenomic studies, led to the identification of the strain as Streptomyces justiciae RA-WS2. The predicted biosynthetic gene clusters further confirmed the presence of the BGC for setomimycin biosynthesis in Streptomyces justiciae strain RA-WS2.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03459-5.

A biostatistical approach for augmenting rare bianthraquinone antibiotic production by Streptomyces sp. RA-WS2 using Taguchi design

Consistent production of bioactives from microbial sources remains a big challenge for fermentation based bio-processes. Setomimycin, a rare 9,9'-bianthrylanthracene antibiotic reported to be active against Gram positive bacteria i.e. Staphyloccocus aureus, Bacillus subtilis, Bacillus cereus, and Mycobacterium smegmatis, including mycobacteria is one of the least exploited antibiotic. Present work aims to enhance and maximize setomimycin production using One Factor at a Time (OFAT) approach, followed by Taguchi L9 orthogonal array (OA) design in 30L fermenter. Four most influential parameters, namely carbon source, nitrogen source, air and agitation were selected for optimization studies. The optimized production medium supplemented with 150 g/L glycerol and 7.5 g/L soyabean meal with an agitation rate of 100 RPM and air flow rate of 20 LPM (Liters Per Minute) resulted in 675 mg/L setomimycin production within 96-108 h of fermentation as compared to the initial production i.e. 40 mg/L. Thus, an overall enhancement of 16.8 folds was achieved in setomimycin production after optimization in 30L fermenter.

Drug repurposing against main protease and RNA-dependent RNA polymerase of SARS-CoV-2 using molecular docking, MM-GBSA calculations and molecular dynamics

A virus called severe acute respiratory distress syndrome coronavirus type 2 (SARS‐CoV‐2) is the causing organism of coronavirus disease 2019 (COVID-19), which has severely affected human life and threatened public health. The pandemic took millions of lives worldwide and caused serious negative effects on human society and the economy. SARS-CoV-2 main protease (Mpro) and RNA-dependent RNA polymerase (RdRp) are interesting targets due to their crucial role in viral replication and growth. Since there is only one approved therapy for COVID-19, drug repurposing is a promising approach to finding molecules with potential activity against COVID-19 in a short time and at minimal cost. In this study, virtual screening was performed on the ChEMBL library containing 9923 FDA-approved drugs, using various docking filters with different accuracy. The best drugs with the highest docking scores were further examined for molecular dynamics (MD) studies and MM-GBSA calculations. The results of this study suggest that nadide, cangrelor and denufosol are promising potential candidates against COVID-19. Further in vitro, preclinical and clinical studies of these candidates would help to discover safe and effective anti-COVID-19 drugs.