Rapid Preparation of Unsheathed Bacterial Flagella

Abstract

The flagellum is required for bacterial swimming and swarming motility. In the biphasic Salmonella enterica serovar Typhimurium (S. Typhimurium), the flagellar filament is build up by two distinct monomeric subunits, flagellin FliC and FljB. S. Typhimurium has the ability to switch between two flagellins, FliC and FljB, in a phase-variable manner. The switch to FliC is called phase H1 and considered important for bacterial growth and survival in the spleen in a murine infection model of typhoid fever. Flagellin is secreted as monomeric subunits, but the majority of flagellin is polymerized upon secretion as the flagellar filament. Salmonella flagellin has traditionally been isolated through a process involving multiple steps of centrifugation and acid treatment. Here, we delineate a simplified protocol for preparing Salmonella´s flagellin for analytical purpose to determine the amount of flagellin without the aid of antibodies. The growth conditions used were stationary phase, logarithmic phase and a low oxygen and high salt condition mimicking the gastrointestinal tract. Flagellin expression of other source organisms, such as other serovars of Salmonella enterica and Escherichia coli, including flagellar phase- or genetic variants can be analysed. Flagellin expression analysis complements flagella-associated phenotype analysis such as swimming and swarming behaviour.