A-B. Bacterial two-hybrid assay. BTH101 reporter cells producing the indicated proteins or domains fused to the T18 or T25 domain of the Bordetella adenylate cyclase were spotted on X-Gal indicator plates. The blue color of the colony reflects the interaction between the two proteins. TolB and Pal are two proteins known to interact but unrelated to the T6SS or the MltE proteins. The experiment was performed in triplicate and a representative result is shown. 