Structural Characterization of the Fla2 Flagellum of Rhodobacter sphaeroides

Abstract

Rhodobacter sphaeroides is a free-living alphaproteobacterium that contains two clusters of functional flagellar genes in its genome: one acquired by horizontal gene transfer (fla1) and one that is endogenous (fla2). We have shown that the Fla2 system is normally quiescent and under certain conditions produces polar flagella, while the Fla1 system is always active and produces a single flagellum at a nonpolar position. In this work we purified and characterized the structure and analyzed the composition of the Fla2 flagellum. The number of polar filaments per cell is 4.6 on average. By comparison with the Fla1 flagellum, the prominent features of the ultra structure of the Fla2 HBB are the absence of an H ring, thick and long hooks, and a smoother zone at the hook-filament junction. The Fla2 helical filaments have a pitch of 2.64 m and a diameter of 1.4 m, which are smaller than those of the Fla1 filaments. Fla2 filaments undergo polymorphic transitions in vitro and showed two polymorphs: curly (righthanded) and coiled. However, in vivo in free-swimming cells, we observed only a bundle of filaments, which should probably be left-handed. Together, our results indicate that Fla2 cell produces multiple right-handed polar flagella, which are not conventional but exceptional. ؊ mutant grown phototrophically and in the absence of organic acids. The Fla1 system produces a single lateral or subpolar flagellum, and the Fla2 system produces multiple polar flagella. The two kinds of flagella are never expressed simultaneously, and both are used for swimming in liquid media. The two sets of genes are certainly ready for responding to specific environmental conditions. The characterization of the Fla2 system will help us to understand its role in the physiology of this microorganism. Motility provides microorganisms with a fundamental survival advantage. Flagella are one of the most complex and effective organelles of locomotion, capable of propelling bacteria through liquids (swimming) and through viscous environments or over surfaces (swarming), and are widely used among Bacteria and Archaea. In addition, these organelles play an important role in adhesion to substrates and biofilm formation, and they contribute to the virulence process in pathogenic bacteria (1, 2).The bacterial flagellum is a rotary motor powered by the electrochemical proton or sodium potential. The morphology of the flagellum is similar among different bacterial species. Nevertheless, there are differences in their substructures, which are not yet clearly understood. The improvement in powerful microscopy techniques has revealed variations in the architecture of the bacterial flagellar motors (3, 4). The bacterial flagellum is a supramolecular complex made of about 30 different proteins with copy numbers that range from a few to thousands. The structure has been divided into three parts: filament, hook, and basal body. The basal body spans the bacterial cell envelope and comprises a rod and a series of rings. In the cytoplasm the basal body for...

Characterization of the relationship between polar and lateral flagellar structural genes in the deep-sea bacterium Shewanella piezotolerans WP3

“…Recently, increasing evidence has indicated that the distribution of the dual flagellar system is more widespread in prokaryotes than previously estimated71314151617181920. Moreover, the origins of the secondary (lateral) flagellar system have been investigated by comparative genomic and phylogenetic analyses21.…”

Architecture of divergent flagellar promoters controlled by CtrA in Rhodobacter sphaeroides

“…It has been shown that the fla1 genes of R. sphaeroides were acquired by horizontal transfer. In contrast, the gene products of the vertically inherited fla2 genes enable, under particular conditions, the synthesis of several polar flagella [ 11 , 13 ]. The expression of the fla1 genes follows a hierarchical expression pattern in which the early genes are expressed under the control of RpoN1 and the activator proteins FleQ and FleT whereas the late genes are dependent on FliA [ 14 ].…”

The CtrA Regulon of Rhodobacter sphaeroides Favors Adaptation to a Particular Lifestyle

“…Phylogenetic analyses suggested that the fla1 genes were acquired through a horizontal gene transfer event from an ancestral gammaproteobacterium, while fla2 genes are alphaproteobacterial in origin (23). The products of the fla1 genes are assembled in a single subpolar flagellum (24); in contrast, expression of fla2 results in multiple polar flagella (23,25). Under the growth conditions commonly used in the laboratory, the fla1 genes are constitutively expressed (24,26) and the expression of fla2 is practically undetectable (23).…”