Growth, acid stress and [35S]-L-methionine labelling. C. jejuni strains were grown to late exponential phase in modified chemically defined broth (CDB) containing 0.01 mM methionine at 37°C in a microaerophilic atmosphere. When cells had reached approximately 1 × 108 CFU/ml, after 26 hours of growth for strains 11168 (A) and 327 (B) and after 22 hours for strain 305 (C), they were subjected to a shift in pH. The cells were first exposed to HCl (pH 5.2, ●) and acetic acid (pH 5.7, ▲) for 20 min before radioactive labelling with [35 S]-L-methionine for an additional 20 min. The control (■) was labelled for 20 min. The arrows indicate the point of labelling. After labelling, cells were harvested for proteome analysis. Data points are the mean of three replicates and standard variations are indicated by ± SEM (n = 3).