Pm regulation through alternative control loops. (a) Pm activation in response to vapors of m-xylene or o-xylene assayed in solid media. Patches of the reporter strain P. putida mt-2 (pSEVA226Pm) were grown on the surface of M9-succinate agar and then exposed to saturating vapors of m-xylene (which triggers the appearance of both XylSh and XylSa), or o-xylene (which makes cells to produce only XylSh). (b) Pm promoter activity deduced from images of panel (a) processed identically as in Fig. 6. (c) Pm activation kinetics in liquid media added with 1 mM 3MBA (m-xylene proxy, leading to both XylSh and XylSa) or 1 mM of 3 MBz (appearance of XylSa only). Promoter activities of reporter strain P. putida mt-2 (pSEVA226Pm) are shown in respect to the maximal value reached with 3MBA induction. (d) Contribution of each regulatory device to Pm activity. The bar diagram compares standardized promoter activities brought about by the XylSa-dependent loop (3 MBz), by the XylS hyper-expression loop (o-xylene induced) and both (m-xylene or 3MBA induced). Promoter activity is represented as the maximal value obtained in every experimental condition relative to the highest m-xylene (or 3MBA) induction value.