Bacterial Strain Culture and Protein Expression

The strains and plasmids used in this study are listed in Supplementary Table S1, and the primers are listed in Supplementary Table S2. All strains of the E. coli W3110 series were cultured in Luria-Bertani (LB) liquid medium or LB medium containing 1.5% agarose at 37°C; YeO9 was cultured in Brain Heart Infusion (BHI) medium containing 1.5% agarose at 30°C; and B. abortus A19 was cultured in Tryptic Soy Broth (TSB) medium or TSB medium containing 1.5% agarose at 37°C. For protein expression, the strains carrying expression plasmids were cultured at 37°C to an OD_{600 nm} of approximately 0.6. Then, 1 mM isopropyl-β-D-thiogalactopyranoside (IPTG) was added at 30°C for 12 h.