Abstract
Flagella-driven motility is an important trait for bacterial colonization and virulence. Flagella rotate and propel bacteria in liquid or semi-liquid media to ensure such bacterial fitness. Bacterial flagella are composed of three parts: a membrane complex, a flexible-hook, and a flagellin filament. The most widely studied models in terms of the flagellar apparatus are E. coli and Salmonella. However, there are many differences between these enteric bacteria and the bacteria of the Pseudomonas genus. Enteric bacteria possess peritrichous flagella, in contrast to Pseudomonads, which possess polar flagella. In addition, flagellar gene expression in Pseudomonas is under a four-tiered regulatory circuit, whereas enteric bacteria express flagellar genes in a three-step manner. Here, we use knowledge of E. coli and Salmonella flagella to describe the general properties of flagella and then focus on the specificities of Pseudomonas flagella. After a description of flagellar structure, which is highly conserved among Gram-negative bacteria, we focus on the steps of flagellar assembly that differ between enteric and polar-flagellated bacteria. In addition, we summarize generalities concerning the fuel used for the production and rotation of the flagellar macromolecular complex. The last part summarizes known regulatory pathways and potential links with the type-six secretion system (T6SS).
Highlights
Flagella are found in many organisms, including Gram-negative and Gram-positive bacteria, Archae, and eukaryotic cells
We focus on the macromolecular machinery of this structure in Pseudomonas species, which have been less extensively studied than the welldescribed flagellar systems of Salmonella and E. coli
It is recognized to play a central role in modulating the transition between planktonic and biofilm lifestyles in a large and growing number of bacterial species, including P. aeruginosa, P. fluorescens, S. enterica, E. coli, and V. cholerae [104]. The concentration of this second messenger depends on diguanylate cyclase (DGC) and phosphodiesterase (PDE) activity; c-di-GMP is produced by DGC from two molecules of guanosine triphosphate (GTP) and is degraded into 5 -phosphoguanylyl-(3 -5 )-guanosine by PDE [102]
Summary
Flagella are found in many organisms, including Gram-negative and Gram-positive bacteria, Archae, and eukaryotic cells. The flagellin filament and chemotaxis are required for the induction of S. enterica colitis in streptomycin pre-treated mice [10] In other microorganisms, such as P. aeruginosa, the flagellar appendage plays a role in virulence by favouring internalization of the pathogen by corneal epithelial cells [11]. Within Gram-negative bacteria, flagella show many differences in terms of their gene names, localization, number, function, expression, and regulatory pathways Such disparity explains the difficulties in summarizing knowledge on the flagellar apparatus. Among Gram-negative bacteria, Salmonella and E. coli species are the most widely studied models for flagella. These bacteria possess flagella (from 5 to 10) located randomly around the cell, called peritrichous flagella [13]. We conclude by summarizing the regulation of Pseudomonas flagella, both their production and function, by extrinsic and intrinsic parameters
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