Fig 5.

Release of proline into the growth medium is not mediated by MscL- and MscS-type channel proteins. Cells of strains JH642 (msc⁺ opuE⁺), BLOB9 (msc⁺ opuE), SMB80 (msc opuE⁺), and TMB105 (msc opuE) were grown to mid-exponential growth phase (OD₅₇₈ of about 2) in either SMM (gray bars) or SMM containing 1 M NaCl (black bars). The proline content of the supernatants was determined by the colorimetric assay described by Bates et al. (2). The error bars given are standard deviations of two separately grown B. subtilis cultures (n = 2). msc mutant strains carry gene disruptions in the mscL, ykuT, yhdY, and yfkC loci, thereby interrupting the single MscL-type channel-forming protein and the three MscS-type channel-forming proteins from B. subtilis (24, 58). opuE mutant strains carry the Δ(opuE::tet)1 allele (56).