Bacterial Flagella

Abstract

Bacteria propel themselves through liquid or over semisolid media using rotation of a propeller‐like organelle, the flagellum. Flagellar rotation is energised by the membrane ion gradient and flagella enable bacteria to swim towards nutrients and away from harmful substances. The flagellum is a sophisticated, molecular nanomachine. To build a flagellum, more than two dozen proteins need to assemble in an ordered process. The accurate size and subunit composition of each substructure of this nanomachine is achieved by coupling gene expression to the assembly state. Major components of the flagellum assemble outside the cytoplasmic membrane. A specialised protein export system, termed ‘type‐III secretion’ transports flagellar substrates across the inner membrane. A flexible coupling structure, the hook, connects the membrane‐embedded basal body to the rigid, extracellular filament. The length of this flexible joint is tightly controlled in Salmonella enterica and hook length is determined by intermittent secretion of a molecular ruler. Key Concepts: Bacteria swim through their environment by rotating an extracellular appendage, the flagellum. Rotation of the flagellum is energised by influx of protons through stator proteins that are attached to the cell body. The bacterial flagellum consists of three major parts: (1) the basal body as the engine, (2) a flexible joint structure that connects the engine to (3) the long external filament. Assembly of the flagellum involves dozens of proteins and the coordination of gene expression to the assembly state of the flagellum. A specialised protein export system, a type‐III secretion apparatus, is responsible for the export of flagellar secretion substrates, for example, most external parts of the flagellum. Protein export via the type‐III secretion system is dependent on the proton‐motive force. The length of the flexible joint structure that connects the filament to the basal body is highly regulated to a final length of 55 nm in Salmonella . A molecular ruler determines the final length and catalyses a switch in secretion specificity from early to late‐substrate secretion mode.

Curcumin Reduces the Motility of Salmonella enterica Serovar Typhimurium by Binding to the Flagella, Thereby Leading to Flagellar Fragility and Shedding

“…It is made up of a hook-basal body, a motor complex, and a filament that is composed of around 20,000 flagellin monomers (1). The formation of the functional flagellar apparatus is highly coordinated and governed by environmental cues (2,3).…”

The immunogenic potential of bacterial flagella for Salmonella‐mediated tumor therapy

“…We deleted the gene coding for FliF, which forms the MS-ring of the flagellar basal body in the inner membrane, 37 or FliHIJ, which is an ATPase complex involved in the export of flagella building blocks. 58 Both strains neither expressed nor secreted flagellin and thus were nonmotile. Interestingly, both strains were highly immunogenic in vitro and in vivo.…”

SPI-1 virulence gene expression modulates motility of Salmonella Typhimurium in a proton motive force- and adhesins-dependent manner

“…Important virulence factors include the flagellum and the injectisome, which is used to deliver effector proteins into host cells [ 2 ]. The flagellum is a rotating motility organelle that enables directed swimming towards nutrients and away from harmful substances [ 3 ]. Moreover, flagella are thought to contribute to Salmonella pathogenesis by enhancing the interaction with the host cell membranes and promoting actin polymerization [ 4 , 5 ].…”