The present study reveals the production of dark, extracellular melanin pigment (386 mg/L) on peptone yeast extract iron agar medium by Streptomyces puniceus RHPR9 using the gravimetric method. UV-Visible, Fourier Transform Infrared (FTIR), and Nuclear Magnetic Resonance (1H) (NMR) spectroscopy confirmed the presence of melanin. Extracted melanin showed antibacterial activity against human pathogens such as Bacillus cereus, Staphylococcus aureus, Pseudomonas aeruginosa, and Escherichia coli except for Klebsiella pneumoniae. A potent free radical scavenging activity was observed at 100 μg/mL of melanin by the DPPH method with a concentration of 89.01±0.05% compared with ascorbic acid 96.16±0.01%. Antitumor activity of melanin was evaluated by MTT assay against HEK 293, HeLa, and SK-MEL-28 cell lines with IC50 values of 64.11±0.00, 14.43±0.02, and 13.31±0.01 μg/mL respectively. Melanin showed maximum anti-inflammatory activity with human red blood cells (hRBC) (78.63 ± 0.01%) and minimum hemolysis of 21.37±0.2%. The wound healing potential of the pigment was confirmed on HeLa cells, cell migration was calculated, and it was observed that cell migration efficiency decreased with an increase in the concentration of melanin. To our knowledge, this is the first evidence of melanin produced from S. puniceus RHPR9 that exhibited profound scavenging, anti-inflammatory and cytotoxic activities.

Seven Bacillus spp. isolated from the marine water and the rhizosphere of the medicinal plant Coscinium fenestratum were studied to produce plant growth promotion (PGP) traits invitro. Among the seven isolates, MMRH22 and RHPR20 produced copious amounts of PGP traits. Based on the 16S rRNA sequence, the two potent bacterial isolates, RHPR20 and MMRH22, were identified as Bacillus mojavensis and Bacillus cereus, respectively. A compatibility test between the isolates RHPR20 and MMRH22 revealed they are compatible and can be used as a consortium. Both isolates were evaluated for the plant growth promotion and the biofortification of sorghum under greenhouse conditions. Treatments included the application of MMRH22, RHPR20, their consortium (RHPR20 + MMRH22), and an uninoculated control. Inoculation with bacterial cultures resulted in a significant increase in the plant height; the number of leaves; the leaf area; the root, shoot, and leaf weight; and the yield of sorghum at 30 and 60 days after sowing (DAS). The scanning electron micrograph of the sorghum plant roots revealed extensive colonization in the plants treated with the bacterial cultures compared to the uninoculated control. The sorghum grains obtained after final harvest were analyzed for their nutrient content by ICP–OES. The biofortification in sorghum grains was varied and was found to enhance the iron content up to 97%. This study revealed that treatments with microbial consortia enhance plant growth, yield, and iron content, which could combat nutrient deficiencies in plants and humans.

The present study involves isolation of Streptomyces spp. from rhizosphere of Coscinium fenestratum Gaertn, an endangered medicinal plant from Western Ghats of Karnataka, India. Four potential isolates were identified by 16S rRNA sequencing as Streptomyces sp. RHPR3, Streptomyces puniceus RHPR9, Streptomyces sp. RHPR14 and Streptomyces mediolani RHPR25. An enrichment culture method was used for the isolation of Streptomyces spp. for biosurfactant activity. Among four potential Streptomyces spp., S. puniceus RHPR9 showed highest Emulsification index (EI) (78±0.2%) and Emulsification assay (EA) (223±0.2 EU mL-1). Thin layer chromatography, Fourier transform infrared spectroscopy (FTIR) and mass spectrometric analysis revealed that as glycolipid. Further confirmed by presence of fatty acids like hexanoic acid methyl ester, decanoic acid by Gas chromatography mass spectroscopy (GC-MS) analysis. S. puniceus RHPR9 showed a significant IAA production (41μg mL-1), solubilized P (749.1 μg mL-1), growth promotion of chilli (Capsicum annuum L.) was evaluated using paper towel method and greenhouse conditions. S. puniceus RHPR9 showed a significant increase in seed vigor index (2047) and increase in plant biomass (65%) when compared to uninoculated control. To our knowledge, this is the first report on epiphytic S. puniceus RHPR9 isolated from an endangered medicinal plant C. fenestratum Gaertn, for biosurfactant production and plant growth promotion activities.

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