The isolation of a novel Streptomyces zaomyceticus and its effects on disease resistance of Ctenopharyngodon idellus

Abstract

This research has identified Streptomyces zaomyceticus S1-6 as a promising probiotic candidate exhibiting broad-spectrum antibacterial properties against nine prevalent fish pathogens. Toxicity assessments conducted using liver cells from grass carp (Ctenopharyngodon idella) and subsequent feeding trials demonstrated that S1-6 is both safe and non-cytotoxic. After a 30-day feeding period, S1-6 significantly enhanced growth performance relative to the control group (P < 0.05). Notably, key non-specific immune enzyme activities-including acid phosphatase (ACP), alkaline phosphatase (AKP), superoxide dismutase (SOD), and lysozyme (LSZ)-were significantly elevated in the treatment group (P < 0.05). Gene expression analysis indicated an upregulation of immune-related genes (IL-8, LSZ, C3) in the kidney and spleen (P < 0.05), while LSZ and C3 exhibited downregulation in the intestine. Challenge experiments involving Aeromonas hydrophila demonstrated a significantly higher survival rate in the S1-6 group compared to the control group (P < 0.05). In vivo imaging confirmed that S1-6 effectively colonized and proliferated in the gills and intestines over 14 days. Whole-genome sequencing revealed the presence of 35 biosynthetic gene clusters, including those associated with thiolutin, istamycin, cypemycin, lankamycin, and streptolydigin, which are likely responsible for the observed antibacterial activity. The antimicrobial compound produced by strain S1-6 was isolated and purified through ultra-high-performance liquid chromatography (UHPLC). LC-MS/MS analysis identified an active substance with a mass-to-charge ratio (m/z) of 432.05 [M+H]⁺, which is hypothesized to be a derivative of Herboxidiene. In summary, S. zaomyceticus S1-6 demonstrates considerable potential for promoting fish growth, enhancing immune responses, and preventing bacterial diseases within aquaculture settings.

Keywords: Aeromonas hydrophila; Ctenopharyngodon idellus; Immune response; Probiotics; Streptomyces zaomyceticus.