Antibacterial and Anticancer Properties of Diketopiperazines from Streptomyces antimicrobicus BN122, an Endophyte in Oryza sativa var. glutinosa.

Abstract

<b>Background and Objectives:</b> This study characterized a bacterial strain, BN122, isolated from the root tissues of purple sticky rice (<i>Oryza sativa</i> L. var. glutinosa). Identified as <i>Streptomyces antimicrobicus</i> based on 16S rDNA analysis and physical-chemical properties, the aim was to isolate and evaluate the antibacterial and anticancer activities of its bioactive compounds. <b>Materials and Methods:</b> The major compounds were purified from BN122's culture extract using column chromatography and TLC. The NMR spectroscopy and mass spectrometry confirmed their identities as Cyclo-(L-Pro-L-Val), Cyclo-(L-Pro-L-Leu), Cyclo-(L-Pro-L-Trp) and Cyclo-(L-Pro-L-Phe). The antibacterial and anticancer activities of these compounds were subsequently assessed. Statistical significance was determined using SPSS software. <b>Results:</b> Isolated compounds exhibited potent antibacterial activity against Gram-positive bacteria. Minimum inhibitory concentrations (MICs) ranged from 32 to 256 μg/mL, while minimum bactericidal concentrations (MBCs) were between 128 and 512 μg/mL. Compounds demonstrated potent cytotoxic activity against cancer cells, with IC₅₀ values ranging from 32.00 to 57.08 μg/mL for MDA-MB-231 cells, 85.73 to 158.93 μg/mL for HeLa cells and 276.89 to 323.48 μg/mL for HepG2 cells. Notably, these compounds exhibited moderate toxicity towards non-cancerous Vero cells (IC₅₀ = 482.73 to 680.87 μg/mL). <b>Conclusion:</b> The findings suggested that <i>Streptomyces antimicrobicus</i> BN122 produces compounds with promising antibacterial and anticancer properties. Further research on these compounds could contribute to developing novel therapeutic strategies for bacterial infections and certain cancers.