Characterization and genome analysis of marine Streptomyces albidoflavus S20 for the biological control of tobacco black shank

• Strain S20, isolated from a marine sponge, demonstrated high antagonistic activity against Phytophthora nicotianae , inhibiting mycelial growth by 90.3% in vitro . • Application of S20 significantly reduced tobacco black shank incidence, achieving biocontrol efficiency of 92.1% in pot trials and 90.4% under field conditions. • The strain was identified as Streptomyces albidoflavus and harbors diverse biosynthetic gene clusters for antifungal and plant-beneficial compounds. • Strain S20 exhibited multiple plant growth-promoting traits, including hydrolytic enzyme production, phosphate solubilization, siderophore secretion, and IAA biosynthesis. • Treatment with S20 enhanced tobacco seed germination, root development, and key physiological indicators, indicating its dual function as a biocontrol and biofertilization agent. Tobacco black shank, a destructive soil-borne disease caused by Phytophthora nicotianae , poses serious threats to global tobacco production. To address this threat, a marine sponge-derived actinomycete, designated strain S20, was isolated and demonstrated potent antagonistic activity against this pathogen. In plate confrontation assays, strain S20 exhibited 90.3 % inhibition of P. nicotianae , and achieved disease control efficiency of 92.1 % and 90.4 % in pot and field trials, respectively. Morphological and molecular characterization identified the strain as Streptomyces albidoflavus . Whole-genome analysis revealed a circular chromosome of 6.73 Mb with 73.12 % GC content, harboring 5,761 protein-coding genes, along with a 218.7 kb plasmid containing 70.47 % GC and 170 open reading frames. AntiSMASH identified numerous BGCs putatively encoding compounds with antifungal, plant growth-promoting, and stress resilience activities. Functional assays showed that strain S20 produced extracellular chitinase, cellulase, β-1,3-glucanase, and protease, in addition to displaying plant-beneficial traits such as nitrogen fixation, phosphate solubilization, siderophore production, and indole-3-acetic acid biosynthesis. Furthermore, treatment with S20 significantly enhanced tobacco seed germination and root elongation, while also increasing the soluble protein content and α-amylase activity. Collectively, our results establish S. albidoflavus S20 as a promising multifunctional biocontrol agent that controls tobacco black shank via direct antagonism and growth promotion, representing a sustainable and effective biocontrol agent.