Herbicidal Characteristics and Structural Identification of the Potential Active Compounds from Streptomyces sp. KRA17-580.

Weeds are notorious plant species exhibiting a harmful impact on crops. Biological weed control is an efficient and environmentally friendly technique, usually constitutes naturally derived compounds, including bioherbicidal metabolites produced by Streptomyces sp. The isolation and structural identification of phytotoxic compounds from Streptomyces have recently been proposed as an effective way to the discovery of novel bioherbicides. In the screening of bioherbicidal agents, isolated Streptomyces strain KRA17-580 demonstrated significant phytotoxic activity against Digitaria ciliaris. Phylogenetic analysis of the 16S rRNA sequence indicated that isolated KRA17-580 is similar to Streptomyces olivochromogenes. The bacterial culture conditions were optimized for temperature, agitation, and initial pH. Streptomyces strain KRA17-580 showed intense phytotoxic activity and high cell mass at an initial pH of 5.5-7.0, more than 150 rpm, and 25-30 °C. The herbicidal compounds isolated from the culture filtrate of strain KRA17-580 were purified by solvent partition, C18, Sephadex LH20 column chromatography, and high-performance liquid chromatography. By 1D-NMR, 2D-NMR, and electrospray ionization mass spectrometry analysis, the 580-H1 and 580-H2 compounds were identified as a cinnoline-4-carboxamide (MW, 173.0490; C9H7N3O2) and cinnoline-4-carboxylic acid (MW, 174.0503; C9H6N2O2), respectively. Only these two herbicidal compounds showed strong phytotoxic activity against D. ciliaris in foliar applications. However, compound 580-H2 was more phytotoxic than 580-H1 and the toxicity was dose-dependent. The herbicidal metabolite KRA17-580 produced by Streptomyces sp. is a new bioherbicidal candidate that may provide a new lead molecule for more efficient phytotoxic compounds.

Isolation, identification and characterization of Streptomyces metabolites as a potential bioherbicide.

Bioactive herbicidal compounds produced by soil microorganisms might be used to creating a bioherbicide for biological weed control. A total of 1,300 bacterial strains were isolated and screened for herbicidal activity against grass and broadleaf weeds. Among primarily selected 102 strains, the herbicidal activity of bacterial fermentation broths from the following three isolates strain-101, strain-128, and strain-329 reduced the growth of D. sanguinalis by 66.7%, 78.3%, and 100%, respectively as compared with control. Phylogenetic analysis of 16S rRNA gene sequencing determined that the strain-329 has 99% similarity to Streptomyces anulatus (HBUM 174206). The potential bioherbicidal efficacy of Streptomyces strain-329 was tested on grass and broadleaf weeds for phytotoxic activity through pre- and post-emergence applications. At pre-emergence application, the phytotoxic efficacy to D. sanguinalis and S. bicolor on seed germination were 90.4% and 81.3%, respectively at the 2x concentration, whereas in the case of Solanum nigrum, 85.2% phytotoxic efficacy was observed at the 4x concentration. The efficacy of Streptomyces strain-329 was substantially higher at post-emergence application, presenting 100% control of grass and broadleaf weeds at the 1x concentration. Two herbicidal compounds coded as 329-C1 and 329-C3 were extracted and purified by column chromatography and high-performance liquid chromatography methods. The active compound 329-C3 slightly increased leaf electrolytic leakage and MDA production as concentration-dependent manner. These results suggest that new Streptomyces sp. strain-329 produced bioherbicidal metabolites and may provide a new lead molecule for production an efficient bioherbicide to regulate grass and broadleaf weeds.