S treptomyces sp. MNP32, a forest-dwelling Actinomycetia endowed with potent antibacterial metabolites

The Actinomycetia isolate, MNP32 was isolated from the Manas National Park of Assam, India, located in the Indo-Burma biodiversity hotspot region of Northeast India. Morphological observations and molecular characterization revealed its identity to be Streptomyces sp. with a 99.86% similar to Streptomyces camponoticapitis strain I4-30 through 16S rRNA gene sequencing. The strain exhibited broad-spectrum antimicrobial activity against a wide range of bacterial human pathogens including WHO-listed critical priority pathogens such as methicillin-resistant Staphylococcus aureus (MRSA) and Acinetobacter baumannii. The ethyl acetate extract was found to disrupt the membrane of the test pathogens which was evidenced through scanning electron microscopy, membrane disruption assay and confocal microscopy. Cytotoxicity studies against CC1 hepatocytes demonstrated that EA-MNP32 had a negligible effect on cell viability. Chemical analysis of the bioactive fraction using gas chromatography-mass spectrometry (GC–MS) showed the presence of 2 major chemical compounds that include Phenol, 3,5-bis(1,1-dimethylethyl)- and [1,1ʹ-Biphenyl]-2,3ʹ-diol, 3,4ʹ,5,6ʹ-tetrakis(1,1-dimethylethyl)- which have been reported to possess antimicrobial activity. The phenolic hydroxyl groups of these compounds were proposed to interact with the carbonyl group of the cytoplasmic proteins and lipids leading to destabilization and rupture of the cell membrane. These findings highlight the potential of exploring culturable actinobacteria from the microbiologically under-explored forest ecosystem of Northeast India and bioactive compounds from MNP32 which can be beneficial for future antibacterial drug development.