Identification and genomic insights into Bacillus siamensis strains with host colonization potential and activity...

Bacterial wilt (BW), caused by Ralstonia solanacearum species complex (RSSC), is considered as one of the most destructive plant diseases worldwide. In this study, two strains of Bacillus siamensis, BB605-1 and BB653, were screened and identified from endophytes in healthy tomato and mangrove plants, respectively.

Both strains demonstrated antagonistic activities against all 16 RSSC strains, representing eight sequevars from various hosts. The growth of RSSC was suppressed by the crude antimicrobial extracts produced by two strains. The pot inoculation experiment revealed the control efficiencies of two strains against tomato bacterial wilt as 59.63% and 63.98%, respectively. After imparting rifampicin resistance to the strains and applying them to tomato plants, both strains successfully established stable colonization in the rhizosphere, roots, stems, and leaves of tomato plants. Additionally, our study demonstrated that both strains exhibited significant plant growth-promoting properties. Complete genome sequencing revealed genome size of 3.868 M bp with 3594 protein-coding genes for BB605-1, and 3.857 M bp with 3600 protein-coding genes for BB653. Genome analysis of both strains identified seven secondary metabolite clusters with known antimicrobial properties and predicted three unknown compounds with potentially novel properties. Genome mining revealed several key genes associated with plant growth regulation, colonization, and biofilm formation, and we also detected these corresponding substances.

These findings provide a compelling case for the application of B. siamensis in agricultural practices. The isolates' multiple capacities to colonize, enhance plant growth, and exert antagonistic effects against BW positions them as highly promising candidates for an integrated biological solution. © 2024 Society of Chemical Industry.