Herbicidal characteristics and structural identification of a potential active compound produced by Streptomyces sp. KRA18–249

The KRA18–249 strain, isolated from a natural recreational forest near Jeongseon, Gangwon-do, when applied to plants induced signs of wilting within 24 h, leading to plant death. The isolated actinomycete was identified as Streptomyces gardneri based on 16S rRNA gene homogeneity analysis. The culture filtrate was solvent fractionated to obtain the active substance, and the active compound 249-Y1 was isolated from the purified fractions via a herbicide activity test using Digitaria ciliaris. NMR and ESI–MS analyses revealed that the molecular formula of 249-Y1 is C20H16O6 [MW = 352.0947] and is an anthraquinone (rubiginone D2) produce by polyketide synthetase system. The active compound 249-Y1 showed strong (100%) herbicidal activity against several weeds at 500 μg mL−1 concentration. Twisting symptoms began to appear within 24 h of treatment and intensified over time. The KRA18–249 strain produced the herbicidal compound under specific culture conditions, that is, at 200 rpm, 35 °C, for eight days at an initial pH of 10. We also found that 249-Y1 inhibited chlorophyll, but was not a radical generator. Overall, the secondary metabolite 249-Y1, produced by KRA18–249, can be used as a new biological agent for weed control. [Display omitted] •Strain KRA18–249 exhibited herbicidal activity that caused wilting within 24 h and plant death•KRA18–249 showed 99.8% homogeneity with Streptomyces gardneri•The active compound 249-Y1 is a polyketide-based material with the molecular formula C20H16O6•249-Y1 showed strong herbicidal activity against weeds at 500 μg mL-1•Optimal culture conditions were 200 rpm, 35 °C, for a duration of eight days, and an initial pH of 10