Quorum quenching activity of endophytic Bacillus sp. EBS9 from Tecomella undulata and its biocontrol applications

This study investigates the quorum quenching (QQ) activity of an endophytic bacterium, Bacillus sp. EBS9, isolated from the native medicinal plant Tecomella undulata of Rajasthan, and its biocontrol potential against the soft rot pathogen Pectobacterium carotovorum subsp. carotovorum (Pcc). QQ activity was confirmed by the loss of violacein pigment in Chromobacterium violaceum (MCC 2290). Quorum quenching metabolites were extracted using ethyl acetate, and the Quorum Quenching Extract (QQE) demonstrated positive activity in assays with C. violaceum CV026 (MCC 2216). HRLC-MS analysis identified diketopiperazines, L,L-Cyclo (leucylprolyl) and Cyclo (L-Phe-L-Pro), which are N-acyl homoserine lactones (AHLs) antagonists competing for LuxR receptor binding sites. In vitro and in planta assays evaluated QQB's biocontrol potential using treatment I (Pcc), treatment II (Pcc + QQB), and a control (sterile water). In the in vitro soft rot attenuation assay showed that treatment I caused severe maceration in vegetable slices, particularly in radish, exhibiting the highest maceration diameter (25.33 ± 3.52 mm) and percentage (46.14 ± 5.70 %). However, co-inoculation with QQB significantly reduced maceration across all tested vegetables. In the plate assay, germination rates decreased to approximately 50 % in both Vigna radiata and Raphanus sativus for treatment I, but improved to 86.67 % in treatment II. The seed vigour and germination indices also improved with QQB treatment in both plant species. In the pot assay after 30 days, in contrast to a 50 % decrease in root and shoot lengths in treatment I, treatment II led to a substantial recovery, with root lengths increase by 112.07 % and 138.76 %, while shoot length by 315.65 % and 163.63 % in V. radiata and R. sativus, respectively. This study highlights the QQ and biocontrol potential of Bacillus sp. EBS9 against P. carotovorum (Pcc), suggesting its promise in effective management of phytopathogens, which is crucial for agricultural productivity while minimizing environmental impact.