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The recently elucidated archaeal flagellum, or archaellum, is analogous—but not homologous—to the bacterial one. In addition to no sequence similarity being detected between the genes of the two systems, the archaeal flagellum appears to grow at the base rather than the tip, and is about 15 nanometers (nm) in diameter rather than 20.
While bacterial cells often have many flagellar filaments, each of which rotates independently, the archaeal flagellum is composed of a bundle of many filaments that rotates as a single assembly. Bacterial flagella grow by the addition of flagellin subunits at the tip; archaeal flagella grow by the addition of subunits to the base.
[45] [46] However, unlike the bacterial flagellum archaellum has not shown to play a role in archaeal biofilm formation. [47] In archaeal biofilms, the only proposed function is thus far during the dispersal phase of biofilm when archaeal cells escape the community using their archaellum to further initiate the next round of biofilm formation.
[16] [17] [18] They provide two of several kinds of bacterial motility. [19] [20] Archaeal flagella are called archaella, and function in much the same way as bacterial flagella. Structurally the archaellum is superficially similar to a bacterial flagellum, but it differs in many details and is considered non-homologous. [21] [15]
The bacterial flagellum shares a common ancestor with the type III secretion system, [125] [126] while archaeal flagella appear to have evolved from bacterial type IV pili. [127] In contrast with the bacterial flagellum, which is hollow and assembled by subunits moving up the central pore to the tip of the flagella, archaeal flagella are ...
[117] [118] [119] They provide two of several kinds of bacterial motility. [120] [121] Archaeal flagella are called archaella, and function in much the same way as bacterial flagella. Structurally the archaellum is superficially similar to a bacterial flagellum, but it differs in many details and is considered non-homologous. [122] [116]
The evolution of bacteria has progressed over billions of years since the Precambrian time with their first major divergence from the archaeal/eukaryotic lineage roughly 3.2-3.5 billion years ago. [ 1 ] [ 2 ] This was discovered through gene sequencing of bacterial nucleoids to reconstruct their phylogeny .
The bacterial flagellum is made of about 20 proteins, with approximately another 30 proteins required for its regulation and assembly. [152] The flagellum is a rotating structure driven by a reversible motor at the base that uses the electrochemical gradient across the membrane for power. [153]