Monisha Khanna Kapur

Numerous bioactive compounds have been reported to be produced by the members of the genus Streptomyces. During our previous studies, Streptomyces sp. strain 196 was tested for its antimicrobial activity, and bioactive compounds produced by this strain were characterized LC–MS and ¹H NMR. To examine the antifungal potential of strain 196 is the goal of the current investigation. Present investigation is focused on exploring antifungal activity of extract of strain 196 (196EA) on membrane disruption potential against two fungi Candida albicans ATCC 90028 and Aspergillus flavus ITCC 5599. Results revealed that the MIC value is higher for A. flavus than for C. albicans which is 450 µg/mL and 250 µg/mL, respectively. Disc diffusion and spot assay also correspond to the values of the MIC for their respective pathogen. In growth curve analysis, lag and log phase are significantly affected by the extract of strain 196. The effects of extract from strain 196 on plasma membrane disruption of Candida albicans and Aspergillus flavus were analyzed in terms of ergosterol quantification assay, cellular leakage, proton efflux measurement (PM-ATPase), plasma membrane integrity assay (PI), and DNA damage assay (DAPI). Results shown that the extract of strain 196 has the potential to inhibit the cell membrane of the both pathogenic fungi which was further confirmed with the help of scanning electron microscopic (SEM) studies.

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 mu g/mL, whereas in ethyl-acetate extract and methanol-extract, it was 250 and 350 mu g/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.

The COVID-19 pandemic caused unprecedented damage to humanity, and while vaccines have been developed, they are not fully effective against the SARS-CoV-2 virus. Limited targeted drugs, such as Remdesivir and Paxlovid, are available against the virus. Hence, there is an urgent need to explore and develop new drugs to combat COVID-19. This study focuses on exploring microbial natural products from soil-isolated bacteria Streptomyces sp. strain 196 and RI.24 as a potential source of new targeted drugs against SARS-CoV-2. Molecular docking studies were performed on holoRdRp and nsp13, two key factors responsible for virus replication factor. Our in silico studies, K-252-C aglycone indolocarbazole alkaloid (K252C) and daunorubicin were found to have better binding affinities than the respective control drugs, with K252C exhibiting binding energy of − 9.1 kcal/mol with holoRdRp and − 9.2 kcal/mol with nsp13, and daunorubicin showing binding energy at − 8.1 kcal/mol with holoRdRp and − 9.3 kcal/mol with nsp13. ADMET analysis, MD simulation, and MM/GBSA studies indicated that K252C and daunorubicin have the potential to be developed as targeted drugs against SARS-CoV-2. The study concludes that K252C and daunorubicin are potential lead compounds that might suppress the inhibition of SARS-CoV-2 replication among the tested microbial compounds and could be developed as targeted drugs against COVID-19. In the future, further in vitro studies are required to validate these findings. Graphical Abstract

Antimicrobial Resistance (AMR) has been recognized as a global health crisis. It occurs when the microbial pathogens develop mechanisms by means of which the existing antibiotics become ineffective against them and the management of infections caused by them become difficult. According to the data of World Health Organization (WHO) the most common multidrug resistant (MDR) microbes include Mycobacterium tuberculosis, Neisseria gonorrhoeae, Staphylococcus aureus, Streptococcus pneumoniae, Pseudomonas aeruginosa, Clostridium difficile, Klebsiella pneumoniae and many more. Overpopulation, globalization, misuse of antibiotics by humans, injudicious use of antibiotics in livestock, poor hygiene standards in hospitals and lack of development of new antibiotics constitute the major causes for the rise in antimicrobial resistance. Although, the development of new antibiotics is considered as a potential solution to tackle the spread of AMR; newer alternative strategies including vaccines, bacteriophages, monoclonal antibodies, other bioactive molecules like peptides and development of effective diagnostic tools are also being explored by scientists to overcome this issue. This global concern thus requires collaborative efforts from countries across the world. Therefore, different organizations like World Health Organization (WHO), Centers for Disease Control and Prevention (CDC), Infectious Diseases Society of America, World Economic Forum are working tirelessly towards the control of AMR.

During our previous investigation, bioactive compounds present in the extract of Streptomyces sp. strain 196 were characterized using LC–MS/MS and ¹H NMR studies. These compounds were K-252-C aglycone indolocarbazole alkaloid, decoyinine, and cycloheximide; the study of these natural drugs against lung carcinoma is still limited. Focus of the current investigation was to study the anticancer effect of strain 196 extract on lung cancer cells (A549). During in vitro studies, anti-proliferative effect of extract was studied using MTT assay in A549 cells. Effect of extract on cell survival was further evaluated using colony assay. Cell death was qualitatively assessed using apoptosis assay. The aftereffect of extract treatment on metastatic potential of cancerous cells was studied using wound closure assay. Effect of extract on the morphology and cytoskeletal arrangement of A549 cells was studied using phalloidin staining. The extract demonstrated concentration and time-dependent cytotoxicity with IC₅₀ value at 0.5 mg/ml (6 h) and 0.15 mg/ml (24 h). The proliferation and metastatic potential of cells, as characterized by MTT and migration assay, decreased over time in a concentration-dependent manner. Discrete changes in cellular morphology were noted as a result of the induced cytotoxicity. Apoptosis assay demonstrated 98.7% cell death at highest concentration of extract (1 mg/ml). During in silico studies, molecular docking revealed that strain 196 compounds are efficiently binding to mutant EGFR form (T790M/L858R) with release of binding energy (∆G) between − 5 and − 6.9 kcal/Mol. In conclusion, strain 196 extract could be a source of therapeutic drugs to treat lung carcinoma.

Consortia of Streptomyces spp. (colonies 169, 194, 165 and 130) used in this study are an efficient producer of secondary metabolites like chitinases and antifungal compounds, which may help in the protection of surplus food from spoilage. Qualitative screening for chitinase production and taxonomy of these colonies were undertaken in our previous studies. In the current study, GC–MS analysis of extract produced from the consortia of Streptomyces strains was done for the identification of antifungal compounds. Treatment of surplus food with activated consortia of Streptomyces spp. has protected powdered food for a month, whereas fresh food (unpowdered) was preserved for two days. A control sample of surplus food (untreated) was kept to check the contamination, which resulted in the growth of three fungi (FP-1, FG-1, and FB-1). Taxonomic characterization of fungi and identification of toxic compounds produced from them were done by ITS amplification and GC–MS analysis, respectively. The study shows that the secondary metabolites from Streptomyces spp. have the potential to protect the food from mycotoxin contamination. Based on literature reports, this is for the first time that bioactive compounds and chitinases produced from Streptomyces are being used for the protection and management of surplus food.

Emergence of MDR ‘superbugs’ inflamed a severe sense of urgency amongst scientists aiming at the discovery of novel potential drug molecules. Bacteria of the genus Streptomyces are really worth investigating for their immense potential to produce natural compounds of pharmaceutical importance. In the present study, the genome of Streptomyces sp. strain 196 was sequenced, studied and secondary metabolite biosynthetic gene clusters (smBGCs) were detected. FAME analysis was used for taxonomic validation of strain 196. Genome of strain 196 was sequenced using the Illumina NextSeq system which has resulted in a draft genome of 7.4 Mb. Rapid annotation using subsystem technology (RAST) results revealed the presence of 6682 CDS, 64 tRNA genes and 7 rRNA genes. Comparative studies revealed that strain 196 have 93.5% nucleotide and 96% protein level similarities with Streptomyces rhizosphaericola 1AS2c. Genome mining using antiSMASH predicted the presence of BGCs responsible for diverse bioactive compound production. The detected gene clusters were two PKS-III, one PKS-I, five NRPS, two hybrid PKS-I/NRPS, one thiopeptide/LAP, and one bacteriocin types. Furthermore, many other types BGCs such as three ectoine, two siderophore, one arylpolyene, two butyrolactone, one lassopeptide, one lanthipeptide and one melanin were also found. The results of this study provides information about genome and BGCs of strain 196, this information is valuable for researchers who are interested in isolation of bioactive compounds and working on heterologous expression of cryptic BGCs for novel bioactive compounds production.