Subcellular location characteristics of the Pseudomonas aeruginosa GGDEF protein, WspR, indicate that it produces cyclic‐di‐GMP in response to growth on surfaces

Abstract

Summary: The Pseudomonas aeruginosa Wsp signal transduction system produces cyclic‐di‐GMP (c‐di‐GMP), an intracellular messenger that stimulates biofilm formation and suppresses motility. The Wsp system is homologous to chemotaxis systems and includes a membrane‐bound receptor protein, WspA, and a response regulator GGDEF protein, WspR, that catalyses c‐di‐GMP synthesis when phosphorylated. We found that the subcellular distributions of fluorescent protein‐tagged WspA and WspR differed markedly from their chemotaxis counterparts. WspA–YFP formed patches in cells whereas WspR–YFP was dispersed when unphosphorylated and formed bright cytoplasmic clusters when phosphorylated. WspR formed clusters in cells of a Δ wspF mutant, a genetic background that causes constitutive phosphorylation of WspR, but was dispersed in cells of a wspA mutant, a genetic background necessary for WspR phosphorylation. In addition, WspR mutated at Asp70, its predicted site of phosphorylation, did not form clusters. C‐di‐GMP synthesis was not required for cluster formation. WspR–YFP was dispersed in liquid‐grown wild‐type cells, but formed clusters that sometimes appeared and disappeared over the course of a few minutes in cells grown on an agar surface. Our results suggest that the compartmentalized production of c‐di‐GMP in response to a stimulus associated with growth on a surface is an important functional characteristic of the Wsp system.