Phenotypic and Genomic Characterization of Bacterial Strain TAM1, a Potential Biocontrol Agent Against Tetranychus...

The two-spotted spider mite, Tetranychus urticae, poses significant agricultural challenges due to its rapid population growth and high capacity for developing chemical resistance. This study evaluated the acaricidal activity of bacterial strain TAM1, isolated from naturally deceased mites in Taiwan. In bioassays, TAM1 caused over 90% adult mite mortality within 48 h. Infected mites showed symptoms of body darkening and deformation of the ventral abdominal crest lines. Enzymatic analysis confirmed significant chitinase and gelatinase activities. Whole genome sequence of TAM1 was acquired with a 5,066,903 bp circular chromosome (CP120954) and a 164,574 bp circular plasmid (CP120955). Refined functional profiling identified a sophisticated enzymatic arsenal including core chitin-active families (GH18, GH20, AA10) and 157 proteases, with a high prevalence of metallopeptidases that correlate with the detected gelatinase activities. Secretome analysis predicted 42 extracytoplasmic proteases primarily utilizing the Sec-dependent pathway, while the presence of multiple CBM50 modules suggests a potential for targeted substrate anchoring. These genomic insights provide a plausible molecular basis for the observed enzymatic potential and the localized ultrastructural disruption of the T. urticae cuticle. The alignment between phenotypic observations, microscopic evidence, enzymatic activities, and genomic data suggests that TAM1 utilizes synergistic, multi-target mechanisms to exert its acaricidal effects. Based on analyses of whole-genome sequence and 16S rRNA gene sequence, TAM1 was tentatively designated as a strain of Kosakonia sacchari. The bacterial strain reported here represents a promising microbial agent for integrated pest management (IPM) programs.