FIG. 5.

Phenotypes of chvI exoS::Tn5 strains overexpressing syrA. (A) Overexpression of syrA restores resistance of chvI(K214T) mutants to high concentrations of tetracycline. Wild type, strains carrying the chvI(K214T) mutation, and either vector control or vector carrying syrA were cultured on LB medium in the presence of 10 μg/ml tetracycline, and the plates were then photographed. (B) The exoS::Tn5 mutation prevents upregulation of the lpsS::uidA transcriptional fusion in the presence of overexpressed syrA. Vector control and vector containing syrA were introduced into wild-type S. meliloti and the exoS::Tn5 mutation containing the lpsS::DW33 insertion (which results in an lpsS::uidA transcriptional fusion). The extracts were then assayed for β-glucuronidase activity as described in Materials and Methods. Lane 1, lpsS::pDW33 harboring pTE3; lane2, lpsS::pDW33 harboring pTE3::syrA; lane 3, lpsS::pDW33 exoS::Tn5 harboring pTE3; lane 4, lpsS::pDW33 exoS::Tn5 harboring pTE3::syrA.