Screening, Identification, and Pigment Characteristics of Actinomycin D-Producing Actinomycetes from Purple Soil in the Sichuan Basin

Background: Natural pigments from microbial sources are a class of compounds with various structures and a wide range of uses, which have become an important source of antibiotic production. Objectives: This study aimed to screen and identify a new type of pigment-producing microorganism from purple soil in the Sichuan Basin. At the same time, this study aimed to purify and identify the produced pigment, preliminarily optimize its fermentation conditions, and characterize its antibacterial activity. Methods: Through morphology, physiology, biochemistry, and molecular sequencing, the strain LS-2 was identified. The pigment was purified by column chromatography, and its antibacterial activity was characterized by a disc diffusion assay. Through the analysis of the ultraviolet-visible (UV-vis) absorption spectrum, infrared (IR) absorption spectrum, and liquid chromatography-mass spectrometry (LC-MS), the yellow pigment was identified. Results: An actinomycin D-producing Streptomyces parvulus was isolated from the purple soil in the Sichuan Basin. Its optimal fermentation conditions were culture at 34°C on Gause’s synthetic medium with pH 6.5, and the yield reached 540 mg/L after 48 hours. The actinomycin D produced by the strain has excellent antibacterial activity against gram-positive (Staphylococcus aureus) and gram-negative (Escherichia coli). Conclusions: A new actinomycin D-producing strain of Streptomyces parvulus LS-2 was isolated and identified. The strain has a high production of actinomycin D, which has excellent antibacterial activity.