Fig. 6: Hms-dependent production of EPS is suppressed by in vivo accumulation of active CpxR~P.

The Congo Red binding assay was used as an indicator of EPS production by various Yptb-YPIII strains. Indicated Yptb strains were grown (with shaking) at 26 °C for 18 h in LB broth lacking NaCl. A 3.5 µL culture containing an equal number of cells via normalisation of optical density at 600 nm was spotted on NaCl-lacking LA that was supplemented with the dye 0.01% (w/v) Congo Red. Images were taken after growth at 26 °C for 24 h. A representative colony from three independent biological and three technical triplicates of each strain is shown. Used as a negative control was the ∆hmsS mutant that contains an in-frame deletion of codons 11–135 in hmsS, a crucial gene for the Hms-EPS matrix synthesis and export. Indicated scale bar (green line) is 1000 µm. Strains: parent (WT), YPIII/pIB102; cpxA null-mutant, YPIII07/pIB102; complemented cpxA/pCpxA⁺, YPIII07/pIB102, pJF067; cpxR null-mutant, YPIII08/pIB102; cpxP null-mutant, YPIII41/pIB102; hmsS null- mutant, YPIII_2238/pIB102; ackA, pta null-mutant, YPIII69/pIB102; ackA, pta and cpxA null-mutant, YPIII49/pIB102; nlpE null-mutant, YPIII34/pIB102.