Isolation and identification of Streptomyces sp. D-6 and its protective effect on Crucian auratus

Fish bacterial diseases seriously endanger the development of aquaculture. As a new type of microecological feed additive, probiotics can effectively improve the growth performance, immunity, and disease resistance of the host.In this study, an actinomycete strain with significant antibacterial activity against fish pathogenic bacteria was screened from Jiemuxi, Yuanling County, Hunan Province.Through 16S rRNA sequencing, whole genome analysis, morphological, physiological and biochemical characteristics analysis, it was identified as a new type of Streptomyces, named Streptomyces sp. D-6. The optimal fermentation time of the strain was the 4th day, and its antibacterial active substances were stable, resistant to high temperature and ultraviolet light, and not affected by proteases.The MIC and MBC values of the fermentation broth and fermentation supernatant were 32 times diluted, and the corresponding antibiotic titers were 1189.95 μg/mL for apramycin and 818.06 μg/mL for kanamycin. A small molecule active substance with a mass-to-charge ratio of 197.20 [ M + H ]⁺ was isolated and identified by high-performance liquid chromatography and mass spectrometry, and its molecular formula was deduced to be C₁₂H₂₅N₂.The strain was safe and non-toxic to cells, and could stably colonize in Carassius auratus and inhibited the proliferation of Aeromonas veronii. After feeding, it was found that the strain effectively increase the specific growth rate of Carassius auratus, and the activities of ACP and CAT in serum were significantly enhanced. The whole genome analysis provides an effective scientific basis for the development and utilization of strain D-6 and lays a foundation for its application in aquaculture.