Re-isolation of endophytic actinomycete from root of Alpinia galanga (L.) Willd. and its production of actinomycin D

Abstract

Endophytic actinomycetes are bacteria live inside plant tissues without causing harm to the plant. They produced various bioactive compounds. Our prior work isolated Streptomyces parvulus Tc022 from the roots of Alpinia galanga, this strain could produce actinomycin. This study aimed to re-isolate and characterize an endophytic actinomycete from the same Alpinia galanga roots in the same location again, and investigate its bioactive compounds. A Streptomyces strain designated AL036 was isolated and identified as Streptomyces parvulus through morphological, biochemical, and 16S rDNA sequence analysis. Similar to Streptomyces parvulus Tc022, this strain exhibited actinomycin D as its major bioactive compound. Media optimization experiments identified a medium (SC) supporting significantly higher actinomycin D production (103.67 mg/L) compared to the initial medium (ISP-2). Further optimization revealed that a specific carbon-to-nitrogen ratio (20 g/L soluble starch and 2 g/L casein) maximized production (199.33 mg/L). Sugar supplementation did not enhance production but influenced fungal growth. Both crude extract and purified actinomycin D exhibited cytotoxicity against cancer and non-cancerous cell lines, with higher activity towards cancer cells. This study isolated a new Streptomyces parvulus AL036, with efficient actinomycin D production akin to Tc022. Media optimization significantly improved production, highlighting the importance of carbon and nitrogen sources. While both crude extract and purified actinomycin D showed cytotoxicity, further research is needed to improve selectivity for cancer cells.