A Streptomyces sp. NEAU-HV9: Isolation, Identification, and Potential as a Biocontrol Agent against Ralstonia solanacearum of Tomato Plants

Abstract

<i>Ralstonia solanacearum</i> is an important soil-borne bacterial plant pathogen. In this study, an actinomycete strain named NEAU-HV9 that showed strong antibacterial activity against <i>Ralstonia solanacearum</i> was isolated from soil using an in vitro screening technique. Based on physiological and morphological characteristics and 98.90% of 16S rRNA gene sequence similarity with <i>Streptomyces panaciradicis</i> 1MR-8^T, the strain was identified as a member of the genus <i>Streptomyces</i>. Tomato seedling and pot culture experiments showed that after pre-inoculation with the strain NEAU-HV9, the disease occurrence of tomato seedlings was effectively prevented for <i>R.</i> <i>solanacearum</i>. Then, a bioactivity-guided approach was employed to isolate and determine the chemical identity of bioactive constituents with antibacterial activity from strain NEAU-HV9. The structure of the antibacterial metabolite was determined as actinomycin D on the basis of extensive spectroscopic analysis. To our knowledge, this is the first report that actinomycin D has strong antibacterial activity against <i>R. solanacearum</i> with a MIC (minimum inhibitory concentration) of 0.6 mg L^-1 (0.48 μmol L^-1). The in vivo antibacterial activity experiment showed that actinomycin D possessed significant preventive efficacy against <i>R. solanacearum</i> in tomato seedlings. Thus, strain NEAU-HV9 could be used as BCA (biological control agent) against <i>R. solanacearum</i>, and actinomycin D might be a promising candidate for a new antibacterial agent against <i>R. solanacearum</i>.