Opposing contributions of polynucleotide phosphorylase and the membrane protein NlpI to biofilm formation by Salmonella enterica serovar Typhimurium

Abstract

CsgD and cyclic-3',5'-di-guanylate are key regulators of biofilm formation in Salmonella enterica serovar Typhimurium. Our results show that polynucleotide phosphorylase and NlpI oppositely altered expression of CsgD. Polynucleotide phosphorylase and NlpI also had opposite effects on the expression of yjcC, which codes for a cyclic-3',5'-di-guanylate phosphodiesterase affecting CsgD expression.

FIG. 1.

Formation of the rdar morphotype in S. Typhimurium on Congo red plates. Plates were seeded as either streaks or drop-on lawns. Incubation was carried out at 28°C for 72 h, except for noncomplemented drop-on lawns, which were read after 48 h.

FIG. 2.

Effects of pnp and nlpI mutations on CsgD and CsgA expression in S. Typhimurium. CsgD and CsgA expression was analyzed by immunoblotting with Coomassie blue-stained 12% SDS-PAGE gels. Relative signal intensities and the ratios thereof are shown for CsgD.

FIG. 3.

Effect of pnp and nlpI mutations on gene expression in S. Typhimurium. Transcript expression ratios for adrA, csgA, csgD, yciR, yhjH, and yjcC mRNA levels as given for the pnp, nlpI, and pnp nlpI mutants in relation to those for the wild type at 8 h postinoculum.

FIG. 4.

Model for the concerted activity of pnp, nlpI, and yjcC in relation to the expression of csgD.