Screening Plant Growth-Promoting Bacteria with Antimicrobial Properties for Upland Rice.

This study explores beneficial bacteria isolated from the roots and rhizosphere soil of Khao Rai Leum Pua Phetchabun rice plants. A total of 315 bacterial isolates (KK001 to KK315) were obtained. Plant growth-promoting traits (phosphate solubilization and indole-3-acetic acid (IAA) production), and antimicrobial activity against three rice pathogens ( NUF001, 2464, and pv. ) were assessed. KK074 was the most prolific in IAA production, generating 362.6 ± 28.0 μg/ml, and KK007 excelled in tricalcium phosphate solubilization, achieving 714.2 ± 12.1 μg/ml. In antimicrobial assays using the dual culture method, KK024 and KK281 exhibited strong inhibitory activity against , and KK269 was particularly effective against . In the evaluation of antimicrobial metabolite production, KK281 and KK288 exhibited strong antifungal activities in cell-free supernatants. Given the superior performance of KK281, taxonomically identified as sp. KK281, it was investigated further. Lipopeptide extracts from KK281 had significant antimicrobial activity against and a minimum inhibitory concentration (MIC) of 3.1 mg/ml against pv. . LC-ESI-MS/MS analysis revealed the presence of surfactin in the lipopeptide extract. The crude extract was non-cytotoxic to the L-929 cell line at tested concentrations. In conclusion, the in vitro plant growth-promoting and disease-controlling attributes of sp. KK281 make it a strong candidate for field evaluation to boost plant growth and manage disease in upland rice.