Fig. 4.

Profiling of the substrate specificity of the EctT transporter. (A) The E. coli strain MKH13 (proU proP betT) carrying the ectT⁺ plasmid pAK9 was grown in MMA at 37°C in the absence (lane 1) or presence of 0.8 M NaCl (lane 2). Osmotically stressed cultures (with 0.8 M NaCl) were assayed for growth protection by the addition of 1 mM either ectoine (lane 3), hydroxyectoine (lane 4), glycine betaine (lane 5), choline (lane 6), carnitine (lane 7), choline-O-sulfate (lane 8), proline (lane 9), DMSA (lane 10), DMSP (lane 11), and proline betaine (lane 12); the optical densities of the cultures were measured after 16 h of incubation at 37°C. (B) Cultures of the E. coli strain MKH13 carrying the ectT⁺ plasmid pAK9 were grown in MMA with 0.8 M NaCl at 37°C with various concentrations of hydroxyectoine (squares), ectoine (triangles), proline (circles), or glycine betaine (diamonds). The optical densities of the cultures were measured after 16 h of incubation at 37°C. The data documented in panels A and B represent typical sets of experiments as judged from two independent biological replicas.