Chemical-in-plug assays with H. pylori wild type G27 (left) and SS1 Δ motB. The topmost "A" plug contains no addition (negative control). Proceeding clockwise the plugs contain 1 mM alanine (B), 10 mM alanine (C), 50 mM alanine (D), 100 mM alanine (E), and a 1:4 dilution of Brucella broth (F). The assay was repeated six independent times; the plates above show one representative assay. Similar results were obtained with wild-type SS1 and non-chemotactic mutants of both SS1 and G27 (data not shown).