Streptomyces antibioticalis, a Novel Species from a Sanitary Landfill Soil

In-silico and in-vitro evaluation of antifungal bioactive compounds from Streptomyces sp. strain 130 against Aspergillus flavus

Streptomyces spp. are considered excellent reservoirs of natural bioactive compounds. The study evaluated the bioactive potential of secondary metabolites from Streptomyces sp. strain 130 through PKS-I and NRPS gene-clusters screening. GC-MS analysis was done for metabolic profiling of bioactive compounds from strain 130 in the next set of experiments. Identified antifungal compounds underwent ADMET analyses to screen their toxicity. All compounds' molecular docking was done with the structural gene products of the aflatoxin biosynthetic pathway of Aspergillus flavus. MD simulations were utilized to evaluate the stability of protein-ligand complexes under physiological conditions. Based on the in-silico studies, compound 2,4-di-tert butyl-phenol (DTBP) was selected for in-vitro studies against Aspergillus flavus. Simultaneously, bioactive compounds were extracted from strain 130 in two different solvents (ethyl-acetate and methanol) and used for similar assays. The MIC value of DTBP was found to be 314 µg/mL, whereas in ethyl-acetate extract and methanol-extract, it was 250 and 350 µg/mL, respectively. A mycelium growth assay was done to analyze the effect of compounds/extracts on the mycelium formation of Aspergillus flavus. In agar diffusion assay, zone of inhibitions in DTBP, ethyl-acetate extract, and methanol extract were observed with diameters of 11.3, 13.3, and 7.6 mm, respectively. In the growth curve assay, treated samples have delayed the growth of fungi, which signified that the compounds have a fungistatic nature. Spot assay has determined the fungal sensitivity to a sub-minimum inhibitory concentration of antifungal compounds. The study's results suggested that DTBP can be exploited for antifungal-drug development.Communicated by Ramaswamy H. Sarma.

Reclassification of 15 Streptomyces species as synonyms of Streptomyces albogriseolus, Streptomyces althioticus, Streptomyces anthocyanicus, Streptomyces calvus, Streptomyces griseoincarnatus, Streptomyces mutabilis, Streptomyces pilosus or Streptomyces rochei

Taxonomic relationships in eight sets of Streptomyces species, (1a) Streptomyces enissocaesilis, Streptomyces plicatus, Streptomyces rochei and Streptomyces vinaceusdrappus, (1b) Streptomyces geysiriensis, (2) Streptomyces luteus and Streptomyces mutabilis, (3) Streptomyces flavoviridis and Streptomyces pilosus, (4) Streptomyces asterosporus and Streptomyces calvus, (5) Streptomyces erythrogriseus, Streptomyces griseoincarnatus, Streptomyces labedae and Streptomyces variabilis, (6a) Streptomyces griseorubens, (6b) Streptomyces matensis, (6c) Streptomyces althioticus, (7) Streptomyces albogriseolus and Streptomyces viridodiastaticus, (8a) Streptomyces humiferus and Streptomyces violaceolatus, (8b) Streptomyces anthocyanicus, Streptomyces coelescens and Streptomyces violaceoruber, were investigated. Type strains within each subset of 1a to 8b shared completely identical 16S rRNA gene sequences. In MLSA, subsets 1a and 1b, 6a to 6c, and 8a and 8b formed an independent clade, respectively, but the evolutionary distances between S. violaceoruber and the other members in set 8 and between S. griseorubens and those in set 6 were 0.022-0.023 and 0.0064-0.0076, respectively. Members in each of the other sets, except for S. labedae, formed an independent clade. In each clade, evolutionary distances between/among the members were <0.007 except for that between S. griseorubens and S. matensis in set 6, suggesting the same species. Digital DNA-DNA relatedness using whole genome sequences and phenotypic similarities supported the synonymies of sets 1 to 3, set 4 except for S. labedae, sets 5 to 7, and set 8 except for S. violaceoruber, respectively. Therefore, S. enissocaesilis, S. geysiriensis, S. plicatus and S. vinaceusdrappus were considered as later heterotypic synonyms of S. rochei; S. luteus as that of S. mutabilis; S. flavoviridis as that of S. pilosus; S. asterosporus as that of S. calvus; S. erythrogriseus and S. variabilis as those of S. griseoincarnatus; S. griseorubens and S. matensis as that of S. althioticus; S. viridodiastaticus as that of S. albogriseolus; S. coelescens, S. humiferus and S. violaceolatus as those of S. anthocyanicus.

Exploitation of potential bioactive compounds from two soil derived actinomycetes, Streptomyces sp. strain 196 and RI.24

Due to emergence of drug resistant pathogens, nearly all available medicines are becoming ineffective against these life threatening pathogens so there is dire need for the discovery of compounds having unique modes of action. During our previous studies, actinomycetes designated as 196 and RI.24 were isolated, screened for bioactive compounds production and characterized using 16S rRNA gene sequencing. Colony 196 was identified as strain of Streptomyces albolongus (100% sequence similarity) and RI.24 as strain of Streptomyces enissocaesilis (100% sequence similarity). In current study, potential bioactive compounds produced by these strains were characterized. Cold extraction method was applied for taking out of bioactive compounds from actinomycetes. Minimum inhibitory concentration (MIC) determination of compounds from these strains showed activity nearly in the range of commercial antibiotics (strain 196 0.0075 mg/ml, RI.24 0.25 mg/ml and chloramphenicol 0.0075 mg/ml, ampicillin 0.025 mg/ml). Structural elucidation of these compounds was carried out using spectroscopic techniques of LC-MS/MS and ¹H NMR. Compounds K-252-C-Aglycone, indolocarbazole alkaloid, decoyinine, cycloheximide were detected from strain 196 whereas daunorubicin, hygromycin B, agecorynin F, indinavir-N-glucuronide and minocycline were identified from strain RI.24.Current study reports these compounds for the first time from strains of Streptomyces albolongus and Streptomyces enissocaesilis. Present investigation also suggests that strains 196 and RI.24 contain polyketide synthase-I (PKS-I) and non-ribosomal peptide synthetase (NRPS) gene clusters which are responsible for the production of bioactive compounds. The results of this study can be used by the scientific world or pharmaceutical industries for the development of new drugs/formulations by applying more advanced techniques.