Characterization and Production of Antimicrobial Compound by Streptomyces Isolated From the Ant Polyrhachis laevissima.

Social insects such as ants, wasps, and bees have been recognized as promising sources of actinomycetes with antimicrobial potential. In a previous study, we isolated an ant-derived Streptomyces strain, LKA04, from Polyrhachis laevissima, which exhibited potent antimicrobial activity. However, the antimicrobial compound produced by this strain had not been previously characterized. Based on phenotypic and genotypic analyses, strain LKA04 was identified as Streptomyces parvulus. Bioassay-guided fractionation led to the successful isolation of the purified antimicrobial compound produced by this strain. HPLC chromatographic comparison with an in-house database, along with NMR and mass spectrometry analyses, identified the active compound as actinomycin D. This compound exhibited broad-spectrum antimicrobial activity against gram-positive bacteria, including Staphylococcus aureus, methicillin-resistant Staphylococcus aureus (MRSA), Bacillus subtilis, Kocuria rhizophila, Enterococcus faecalis, and Listeria monocytogenes. It also demonstrated activity against gram-negative bacteria such as Klebsiella pneumoniae and Acinetobacter baumannii, as well as the yeasts Candida albicans and Candida glabrata. The highest yield of actinomycin D (217 mg/L) was achieved when S. parvulus LKA04 was cultured in glutamic acid-histidine-fructose mineral salts broth at 30°C under shaking conditions (180 rpm) for 14 days. This study highlights the potential of ant-derived actinomycetes as valuable sources of antimicrobial compounds and underscores the need for continued investigation to further advance our understanding of their biosynthetic capabilities and pharmaceutical potential.