Figure 6. Inactivation of ldtR_Smc or ldtP_Smc increases sensitivity to osmotic stress.

(A) Growth of wild type, SMP1, and SMP2 strains of S. meliloti on osmotic stress plates. Cultures were grown on LB medium until reached OD₆₀₀ = 1.0, and then spot plated in serial dilutions, as indicated at the top of each panel. Pictures are representative of three biological replicates and were taken after 72 h of growth. Black bars correspond to control conditions, white bars 0.3 M sucrose, and grey bars 0.4 M NaCl. (* p<0.05). (B) The transcriptional activity of the different promoters was followed using the β-glucuronidase reporter in SMP1 and SMP2 disruption mutants (Table 2), as well as SMP3 strain (wild type-phenotype). Cultures were grown until mid-exponential phase in M9-glucose with increasing concentration of NaCl (9, 15, 50, 100, 170, and 250 mM; light gray to dark gray). β-glucuronidase activity was expressed as µM p-nitrophenol min⁻¹ OD₆₀₀ ⁻¹. (C) Growth of SMP2A, SMP2B, and SMP2C strains of S. meliloti (Table 2) on osmotic stress plates. Cultures were grown on LB medium until reached OD₆₀₀ = 1.0, and then spot plated in serial dilutions, as indicated at the top of each panel. Pictures are representative of three biological replicates and were taken after 72 h of growth. Black bars correspond to control conditions, white bars 0.3 M sucrose, and grey bars 0.4 M NaCl. (* p<0.05).