Figure 1.

MepS and MepM are required for bacterial growth only in the LB medium. (A) Only the mepS mepM double mutant is lethal in the LB medium. Indicated strains were serially diluted from 10⁸ to 10⁴ cells/ml in 10-fold steps and spotted onto an LB plate. (B) Normal growth of the mepS mepM double mutant in the M9 minimal medium. Indicated strains were serially diluted from 10⁸ to 10⁴ cells/ml in 10-fold steps and spotted onto an LB plate (LB), an M9 minimal medium plate containing 0.2% glucose (Glc MM), an M9 minimal medium plate containing 0.2% glucose and 1% casamino acid, or an M9 minimal medium plate containing 0.2% glucose, 1% casamino acid, and 10 mM tryptophan. (C) Salt sensitivity of the mepM mutant is abolished in the M9 minimal medium. Indicated strains were serially diluted from 10⁸ to 10⁴ cells/ml in 10-fold steps and spotted onto LB plates containing the indicated concentrations of NaCl or M9 minimal medium plates containing 0.2% glucose and the indicated concentrations of NaCl.