Proteomic Insights into the Antibacterial Mechanism of <i>Brevibacillus brevis</i> HK544 Producing Edeine B<sub>1</sub> against <i>Erwinia amylovora</i>

Recently, we reported that Brevibacillus brevis HK544, which produces edeine B1 (EB1), exhibits promising antimicrobial activity against plant pathogens. To elucidate its antibacterial mechanisms against Erwinia amylovora, the causal agent of fire blight, we conducted label-free shotgun proteomic analysis of E. amylovora TS3128 treated with B. brevis culture filtrate (CF) or purified EB1. Comparative analysis showed significant (over twofold) changes in 45 of 624 and 81 of 846 quantified proteins following CF and EB1 treatments, respectively. Functional categorization revealed altered abundances of proteins associated with energy production, ribosome biogenesis, and cell wall/membrane/ envelope biogenesis in both treatments. Notably, 42 and 75 translation-related proteins were differentially expressed in CF- and EB1-treated samples, respectively, consistent with the proposed translation-inhibitory activity of EB1. These findings provide insights into the cellular targets and antibacterial mode of action of B. brevis HK544 and EB1, supporting their potential as biocontrol agents against fire blight.