However, its activity depends on environmental stimuli (e.g., cyclic AMP levels, temperature, heat shock, osmolarity, membrane

biosynthesis, and H-NS protein [8]), cell division, flagella formation, and motility [9–11]. A number of Gram-negative pathogenic bacteria have evolved a specialized type III protein secretion system to deliver effector virulence proteins into host cells [12, 13]. There learn more are two types of type III secretion systems: the translocation-associated type III secretion system (T3aSS) and the bacterial flagellum type III secretion system (T3bSS). The various bacterial type III secretion systems characterized thus far all have Sec independence, ATPase dependence, presence of a hollow filamentous organelle that extends from the outer membrane, a cell-envelope-spanning secretion channel, and nine conserved proteins [14]. The bacterial flagellum type III secretion system also serves as the bacterial flagellum (a biological nanomachine with an ion-powered rotary motor). For the flagellum, the T3bSS apparatus functions to secrete components including the rod, hook, and filament subunits for extracellular assembly. The core of the flagellum is hollow, and secreted subunits polymerize at the growing end of the flagellum. A cap at the tip of the flagellum ensures efficient polymerization Dabrafenib of secreted subunit proteins [15, 16]. This secretion

apparatus is just one mechanism utilized by Gram-negative plant and animal pathogens for the secretion and translocation of virulence determinants into susceptible eukaryotic cells [17]. In Salmonella typhimurium, the expression of class 1 genes (i.e., flhD and flhC) activates expression of Cyclin-dependent kinase 3 genes required for flagella assembly and regulates expression class 2 genes (e.g., fliAZY and flhBAE), which in turn regulates expression of class 3 genes encoding flagellar structural proteins (e.g., fliC, flgMN, and MotAB) [18].

In Xenorhabdus nematophila, it was shown that the EnvZ-OmpR-FlhDC-FliA regulatory network coordinately controls flagella synthesis as well as exoenzyme and antibiotic production [8]. In this paper, we describe the transcriptional regulation of fliC and flhA expression by flhD/C and also show that flhD/C has an effect on extracellular secretion of the Carocin S1 protein, but not on Carocin S1 gene expression. Our results indicate that the type III secretion system of Pectobacterium carotovorum subsp. carotovorum has a new secretory function. Methods Bacterial strains, plasmids, media, and growth conditions The strains and plasmids used are shown in Table 1. Pectobacterium carotovorum subsp. carotovorum strains were propagated at 28°C in 1.4% nutrient agar (NA) or with shaking in Luria-Bertani (LB) medium with NaCl (5 g/L). E. coli strains were propagated at 37°C in LB medium with shaking. Rifampicin, kanamycin, and ampicillin (all at 50 mg/L) were added to either medium when necessary.