Actinobacteria, and the genus Streptomyces in particular, are the workhorses of natural product drug discovery. Most commercially available antibiotics trace their origins to these filamentous soil bacteria, which deploy complex secondary metabolites as chemical weapons against rivals. Marine strains, however, have evolved under conditions of high salinity, variable pressure, and intense microbial competition, and their metabolites often carry chemical features unseen in terrestrial relatives. With resistance to existing antibiotics rising and many current therapeutics burdened by adverse effects, the researchers argue that the ocean floor remains a rich and underexploited reservoir of novel bioactive molecules.

The journey began in July 2015, when the team collected marine soil samples from the Southeast coast of Tamil Nadu and transported them to the laboratory in sterile containers mixed with seawater. Ten grams of each sample were diluted in sterile marine water, shaken for 24 hours, serially diluted, and spread onto starch casein agar plates, which were incubated at 27 degrees Celsius for five to seven days. Powdery actinomycete colonies appeared on the higher dilution plates, and one isolate, VITND1, stood out during subsequent screening. Gram staining revealed purple filamentous structures, and scanning electron microscopy captured the characteristic spore chains and hyphal architecture that define the genus, leading the team to classify the organism as Streptomyces sp.

To assess its antibacterial punch, the researchers first used a cross-streak assay against five clinical pathogens and then tested an ethyl acetate extract of the strain’s fermentation broth using the agar well diffusion method. The results were striking. At a concentration of 1000 micrograms per milliliter, the crude extract produced a zone of inhibition of 19.6 millimeters against Pseudomonas aeruginosa, a notorious hospital pathogen notorious for its multidrug resistance, and 17.6 millimeters against Escherichia coli. Salmonella typhi, Bacillus subtilis, and Staphylococcus aureus were also inhibited, with zones of 14.5, 11.6, and 9.6 millimeters respectively. Chloramphenicol served as the positive control, confirming the assay’s sensitivity.

The bioactivity did not stop at bacteria. In a DPPH free radical scavenging assay, the extract neutralized 72 percent of the stable free radicals at 1000 micrograms per milliliter, a respectable showing against the 98 percent achieved by the reference antioxidant ascorbic acid. Using a human red blood cell membrane stabilization assay, a standard proxy for anti-inflammatory potential, the extract protected 56 percent of cells from hemolysis at 250 micrograms per milliliter, with the drug serratiopeptidase as the benchmark. Most impressive was the antidiabetic screen: the extract inhibited the carbohydrate-digesting enzyme alpha-amylase by 91 percent at the highest concentration tested, approaching the performance of the clinical drug acarbose. Together, the assays painted a picture of a single microbial extract with four distinct pharmacological profiles.

To find out which molecules were responsible, the team subjected the crude extract to gas chromatography-mass spectrometry, identifying 49 different compounds against the NIST08 and WILEY8 spectral databases. Rather than testing all of them blindly, the researchers applied the OSIRIS computational tool to predict molecular properties and toxicity, filtering the list down to 15 active candidates. These were retrieved from the PubChem database, energy-minimized with the CORINA software, and prepared for docking studies against eight protein targets drawn from the Protein Data Bank, spanning bacterial cell division proteins, the human metabolic enzyme CYP3A4, the inflammatory enzyme cyclooxygenase-2, and the diabetes-related nuclear receptor PPAR-gamma.

The docking calculations, performed with AutoDock 4.2 using the Lamarckian genetic algorithm, revealed binding energies ranging from about -2.2 to -8.7 kilocalories per mole across the different protein-ligand pairs. Three molecules emerged as clear leaders. Molecule 1, PubChem CID 4916205, an indole-derived compound, bound the bacterial cell division protein FtsZ with an energy of -8.07 kilocalories per mole, forming a hydrogen bond with arginine 143 and hydrophobic contacts with phenylalanine 183 and arginine 184. Because FtsZ polymerization is essential for bacterial cell division, the authors suggest that this compound may sabotage the bacterial division machinery, consistent with the strong growth inhibition observed against Pseudomonas aeruginosa and E. coli in the petri dish.

The other two standouts told equally compelling stories. Molecule 10, PubChem CID 542106, a carbamic acid derivative previously reported from plants and macroalgae with known antibacterial and antifungal activity, docked into the catalytic site of CYP3A4 with strong affinity, forming hydrogen bonds with arginine 212, alanine 305, and cysteine 442, and engaging a cluster of hydrophobic residues. The authors interpret this as a possible route by which the extract counters oxidative stress through modulation of oxidative metabolism. Molecule 6, PubChem CID 101687, better known as ambreinolide, a natural terpenoid familiar from the perfume industry, delivered a double performance. It bound the inflammatory enzyme COX-2 with the strongest affinity of the entire study at -8.66 kilocalories per mole, hydrogen bonding with lysine 532, and it also docked into PPAR-gamma at -6.25 kilocalories per mole, contacting lysine 230, a residue crucial for receptor activation. This dual evidence suggests the compounds may improve glycemic control by combining alpha-amylase inhibition with PPAR-gamma modulation, while the COX-2 interaction plausibly underlies the membrane-stabilizing anti-inflammatory effect measured in vitro.

Indole derivatives of the kind represented by Molecule 1 have previously been linked to increased insulin sensitivity and activation of glycogen synthase, lending external support to the antidiabetic signal observed here. Ambreinolide, meanwhile, has a long history of use in traditional medicine and fragrance chemistry, but its appearance in a marine Streptomyces metabolite profile highlights how microbial and plant chemistries can converge on the same scaffolds. The authors caution that docking energies and enzyme assays are only the beginning; binding scores do not guarantee efficacy in living systems, and crude extracts contain mixtures whose components may act synergistically or antagonistically in ways that single-molecule screens cannot capture.

Even so, the study offers a coherent proof of concept that integrating in vitro bioassays with in silico docking can rapidly triage microbial extracts and pinpoint lead compounds for development. The team’s next steps include molecular characterization of the isolate, strain improvement and fermentation optimization to boost metabolite yields, molecular dynamics simulations of the protein-ligand complexes, and rigorous in vitro and in vivo testing of the three lead molecules. If those efforts succeed, a bacterium scooped from Indian coastal sand could one day contribute to new treatments for infections, inflammation, and diabetes, a reminder that in the race against drug resistance, some of the most promising candidates may still be waiting quietly in the mud.

Subject of Research: Bioactive secondary metabolites from the marine bacterium Streptomyces sp. VITND1 and their antibacterial, antioxidant, anti-inflammatory, and antidiabetic properties

Article Title: In silico, molecular docking and in vitro bioactivity of compounds extracted from marine Streptomyces sp. VITND1

Article References: In silico, molecular docking and in vitro bioactivity of compounds extracted from marine Streptomyces sp. VITND1. (n.d.). https://doi.org/10.1186/s44315-025-00046-6

Image Credits: AI Generated

DOI: 10.1186/s44315-025-00046-6

Keywords: Streptomyces, marine actinomycetes, molecular docking, GC-MS, antibacterial activity, antioxidant, anti-inflammatory, antidiabetic, natural products, drug discovery, FtsZ, PPAR-gamma