Completion of the hook–basal body complex of the Salmonella typhimurium flagellum is coupled to FlgM secretion and fliC transcription

Abstract

SummaryThe flhDC operon of Salmonella typhimurium is the master control operon required for the expression of the entire flagellar regulon. The flagellar master operon was placed under the tetracycline-inducible promoter P tetA using the T-POP transposon. Cells containing this construct are motile in the presence of tetracycline and non-motile without inducer present. No flagella were visible under the electron microscope when cells were grown without inducer. The class 1, class 2 and class 3 promoters of the flagellar regulon are temporally regulated. After addition of tetracycline, the class 1 flhDC operon was transcribed immediately. Transcription of flgM (which is transcribed from both class 2 and class 3 promoters) began 15 min after induction. At 20 min after induction, the class 2 fliA promoter became active and intracellular FliA protein levels increased; at 30 min after induction, the class 3 fliC promoter was activated. Induction of fliC gene expression coincides with the appearance of FlgM anti-sigma factor in the growth medium. This also coincides with the completion of hook±basal body structures. Rolling cells first appeared 35 min after induction, and excess hook protein (FlgE) was also found in the growth medium at this time. At 45 min after induction, nascent flagellar filaments became visible in electron micrographs and over 40% of the cells exhibited some swimming behaviour. Multiple flagella assemble and grow on individual cells after induction of the master operon. These results confirm that the flagellar regulatory hierarchy of S. typhimurium is temporally regulated after induction. Both FlgM secretion and class 3 gene expression occur upon completion of the hook±basal body structure.

Real-time imaging of type III secretion: Salmonella SipA injection into host cells

“…1 A and B) and require Ϸ100-600 sec to deliver this cargo into the host cell, which roughly corresponds to translocation rates between 7 and 60 molecules per sec (see Supporting Materials and Methods). Although variable, SipA transport rates seem to be in the same order of magnitude as the flagellin transport rates during assembly of the phylogenetically related flagella system [20-40 flagellin per sec (21,22)]. Future work will have to determine whether one or more of the 10-100 SPI-1 TTSS present on each bacterium (23) contribute to injection and whether the number of TTSS participating in transport dictates the overall injection rate.…”

Mathematical model of flagella gene expression dynamics in Salmonella enterica serovar typhimurium

“…Rather, our model assumes a continuous increase/decrease in HBB amounts, and consequently secretion. While this assumption is clearly an over-simplification of the assembly process, there is little data available on dynamics of HBB assembly inside a cell (Karlinsey et al 2000b). In the absence of these details, our model proceeds with this over-simplified assumption.…”

“…In addition, all earlier gene expression dynamics modeling efforts have focused on studying the transition from a non-flagellated to a flagellated state in Salmonella. However, experimental evidence suggests that the class 1 promoter in Salmonella, unlike in E. coli, is never in the OFF state, (Karlinsey et al 2000b) and hence, a typical OFF to ON transition does not capture the physiological state of the organism.…”

“…Flagella are located peritrichously on the bacterium's surface, and number between 6 and 8 per cell (Karlinsey et al 2000b). Assembly of a functional flagellum involves expression from more than 50 genes located at different regions on the chromosome (Chilcott and Hughes 2000).…”

Break on through to the other side: outer membrane penetration of the nascent flagellum by a stop-polymerization mechanism: Figure 1.

“…Completion of the hook-basal body substructure (HBB) is accompanied by a switch in the secretion specificity from the subunits of early flagellar structures, such as the rod subunits, to a later subset that includes the FlgM regulator and the flagellins that are assembled into the filament ( Fig. 1B; Karlinsey et al 2000). FlgM is an inhibitor of 28 -dependent transcription of flagellin genes (Gillen and Hughes 1991).…”