Insecticidal characteristics and structural identification of the potential active compounds from Streptomyces sp. KR0006: Strain improvement through mutagenesis.

Pest control by biological means is an effective, eco-friendly, and promising method that typically involves compounds naturally derived from actinomycetes. Thus, the present study aimed to screen, characterize, and identify the structure of insecticidal compounds from Streptomyces sp. KR0006 and increase the activity through mutagenesis. In the examination of the insecticidal activity level of the isolates, Streptomyces sp. KR0006 metabolite showed significant activity against larvae and moths of Plutella xylostella. Taxonomic analyses of the 16S rRNA gene sequences revealed that the isolated KR0006 strain tended to be 99% consistent with Streptomyces cinereoruber strain NBRC 12756. Three active compounds isolated from the culture filtrate of KR0006 were purified by solvent partition, mid-pressure liquid chromatography (MPLC), Sephadex LH20 column chromatography, and high-performance liquid chromatography (HPLC). By performing 1H-NMR, 13C-NMR, and 2D-NMR experiments, and high-resolution electrospray ionization mass spectrometry analysis, the 316-HP2, 316-HP3, and 316-HP5 compounds were inferred as antimycin A3a (MW, 519.; C26H36N2O9), antimycin A8a (MW, 534; C27H38N2O9), and antimycin A1a (MW, 548; C28H40N2O9) respectively. Mutant U67 obtained from exposure to ultraviolet (UV) irradiation (254 nm, height 17 cm) for 70 seconds resulted in a 70% more larval mortality than that of the initial wild culture. The second mutation of the culture broth enhanced insecticidal activity by 80 and 100% compared with the first mutation and initial medium, respectively. Our study found that Streptomyces sp. KR0006 strain produces insecticidal active compounds and could be used for practical pest management.

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.

Impact of Organic Manure on Growth, Nutrient Content and Yield of Chilli Pepper under Various Temperature Environments.

Expected climatic changes likely elicit serious challenges for crop production. Therefore, it is indispensable to investigate the response of crop growth parameters and yield under temperature variability environments. The current experiment on chilli pepper growth was conducted in a field, rain-shelter plastic house, and plastic greenhouse, with accumulated temperatures of 2832 °C, 2967 °C, and 3105 °C in 2017; and 2944 °C, 3091 °C, and 3168 °C in 2018 growing seasons. Based on soil analysis, 132.7 kg ha-1 (1× of livestock manure compost as an optimum and 265.4 kg ha-1 (2×) as a double amount of organic matter were applied to each simulated temperature condition. The results showed that organic manure application favorably affects the growth attributes and nutrient uptake of chilli pepper with the highest values found in the plastic greenhouse, followed by the rain-shelter house, over the open field cultivation condition. The highest growth of chilli pepper was at the 2× rate of organic manure application, whereas the highest yield was found at the 1× rate of organic manure application. The application of organic manure at the 1× rate in the greenhouse increased root, shoot, and fruit dry weights of chilli pepper by 21.4%, 52.4%, and 79.7%, respectively, compared to the control values. These results indicate that the rational use of organic amendments might be the best solution for chilli pepper production under variable climate conditions.