Regulation of dgcZ in EPEC E2348/69 and the effect of partially deleting its CZB domain on the type III secretion system

Enteropathogenic Escherichia coli (EPEC) is a common cause of childhood diarrhea in developing countries. Extensive studies have established the role of virulence factors, such as the type III secretion system encoded by the locus of enterocyte effacement (LEE), in intestinal colonization and the central mechanisms that control their expression. However, the role of the second messenger c-di-GMP in virulence gene regulation in EPEC remains poorly understood, despite the extensive repertoire of genes encoding enzymes involved in its synthesis and degradation. In this work, we examined the regulation and role of DgcZ, a highly conserved diguanylate cyclase in commensal and pathogenic E. coli strains, in LEE gene regulation in the prototype EPEC strain E2348/69. Using reporter fusions of the dgcZ upstream regulatory region to the cat reporter gene, we first compared dgcZ promoter activity. A DgcZ deletion, partially lacking the CZB domain (DgcZ-∆NT), was constructed. Unexpectedly, the EPEC type III secretion system remains active when this deletion is introduced into EPEC growing under non-inducing conditions (LB medium). Whether this phenotype is caused by a protein-protein interaction between DgcZ lacking the CZB domain (DgcZ-∆NT) and an unknown effector remains to be determined.