Multiple Flagellin Proteins Have Distinct and Synergistic Roles in Agrobacterium tumefaciens Motility

Abstract

Rotary flagella propel bacteria through liquid and across semisolid environments. Flagella are composed of the basal body that constitutes the motor for rotation, the curved hook that connects to the basal body, and the flagellar filament that propels the cell. Flagellar filaments can be composed of a single flagellin protein, such as in , or made up of multiple flagellins, such as in The four distinct flagellins FlaA, FlaB, FlaC, and FlaD produced by wild-type are not redundant in function but have specific properties. FlaA and FlaB are much more abundant than FlaC and FlaD and are readily observable in mature flagellar filaments, when either FlaA or FlaB is fluorescently labeled. Cells producing FlaA with any one of the other three flagellins can generate functional filaments and thus are motile, but FlaA alone cannot constitute a functional filament. In mutants that manifest swimming deficiencies, there are multiple ways by which these mutations can be phenotypically suppressed. These suppressor mutations primarily occur within or upstream of the flagellin gene or in the transcription factor regulating flagellin expression. The helical conformation of the flagellar filament appears to require a key asparagine residue present in FlaA and absent in other flagellins. However, FlaB can be spontaneously mutated to render helical flagella in the absence of FlaA, reflecting their overall similarity and perhaps the subtle differences in the specific functions they have evolved to fulfill. Flagellins are abundant bacterial proteins comprising the flagellar filaments that propel bacterial movement. Several members of the alphaproteobacterial group express multiple flagellins, in contrast to model systems, such as with , which has one type of flagellin. The plant pathogen has four flagellins, the abundant and readily detected FlaA and FlaB, and lower levels of FlaC and FlaD. Mutational analysis reveals that FlaA requires at least one of the other flagellins to function, as mutants produce nonhelical flagella and cannot swim efficiently. Suppressor mutations can rescue this swimming defect through mutations in the remaining flagellins, including structural changes imparting helical shape to the flagella, and putative regulators. Our findings shed light on how multiple flagellins contribute to motility.

The flagella of ‘Candidatus Liberibacter asiaticus’ and its movement in planta

“…In this way, FlaA and at least one secondary flagellin are required for assembling a functional flagellar filament in R. lupini and S. meliloti (Scharf et al, 2001). Similar results were demonstrated in A. tumefaciens (Mohari et al, 2018). Thus, the unique features of Las in FlgJ and FlaA are probably critical to functionality of its flagella.…”

“…1 and Table 1) showed the following characteristics that are shared by all bacterial species in Rhizobiaceae: (i) lack of cytoplasmic chaperone FliJ and the components of export apparatus FliH/FliO; (ii) the function of FliK is performed by MotD (Eggenhofer et al, 2006); (iii) the rod-capping FlgJ protein lacks the muramidase domain in its carboxy-terminus (Herlihey et al, 2014); and (iv) lack of FliD, the filament cap (Table 1). It is important to note that all the traits cited above are shared by members of Rhizobiaceae that are known to contain flagellar apparatus and show swimming behaviour, such as A. tumefaciens and S. meliloti (Attmannspacher et al, 2005;Deakin et al, 1999;Mohari et al, 2018).…”

“…The number of flagellin-encoding genes in bacterial genomes varies and may range between one (Escherichia coli) and seven (Vibrio parahaemolyticus) (Fedorov and Kostyukova, 1984;Kim and McCarter, 2000;Stewart and McCarter, 2003). The flagellar filaments in E. coli K-12 are built up from only one flagellin protein (FliC) (Turner et al, 2012), whereas Bdellovibrio bacteriovorus (Thomashow and Rittenberg, 1985), Campylobacter coli (Guerry et al, 1990), Caulobacter crescentus (Driks et al, 1989), Agrobacterium tumefaciens (Deakin et al, 1999;Mohari et al, 2018), Rhizobium lupini strain H13-3 and Sinorhizobium meliloti have at least two flagellin proteins forming their flagellar filaments (Scharf et al, 2001).…”

Flagella-Driven Motility of Bacteria

“…The flagellar filament of Rhizobium leguminosarum comprises three major proteins, FlaA, FlaB, and FlaC, and four minor proteins, FlaD, FaE, FlaH, and FlaG [28]. Agrobacterium tumefaciens also possesses four flagellins, FlaA, FlaB, FlaC, and FlaD; FlaA and FlaB are abundant in the filament in comparison with FlaC and FlaD, and the swimming ability of A. tumefaciens is considerably decreased by a loss of FlaA but not by that of FlaB [29]. Bradyrhizobium diazoefficiens has two flagella systems: One is subpolar flagella, of which filament is composed of four flagellins, FliC1, FliC2, FliC3, and FliC4, whereas the other is lateral flagella, of which filament is made up of two flagellins, LafA1 and LafA2 [30].…”

Comparative Analysis of Ionic Strength Tolerance between Freshwater and Marine Caulobacterales Adhesins

“…Different bacterial species harbor an adhesive holdfast and use it to attach to surfaces (2,3,9,50,51). They represent an extremely diverse group in terms of their physiologies and the natural environments they inhabit (soil, freshwater, and marine environments).…”