Abstract
Halophilic archaea from the genus Halorubrum possess two extraordinarily diverged archaellin genes, flaB1 and flaB2. To clarify roles for each archaellin, we compared two natural Halorubrum lacusprofundi strains: One of them contains both archaellin genes, and the other has the flaB2 gene only. Both strains synthesize functional archaella; however, the strain, where both archaellins are present, is more motile. In addition, we expressed these archaellins in a Haloferax volcanii strain from which the endogenous archaellin genes were deleted. Three Hfx. volcanii strains expressing Hrr. lacusprofundi archaellins produced functional filaments consisting of only one (FlaB1 or FlaB2) or both (FlaB1/FlaB2) archaellins. All three strains were motile, although there were profound differences in the efficiency of motility. Both native and recombinant FlaB1/FlaB2 filaments have greater thermal stability and resistance to low salinity stress than single‐component filaments. Functional supercoiled Hrr. lacusprofundi archaella can be composed of either single archaellin: FlaB2 or FlaB1; however, the two divergent archaellin subunits provide additional stabilization to the archaellum structure and thus adaptation to a wider range of external conditions. Comparative genomic analysis suggests that the described combination of divergent archaellins is not restricted to Hrr. lacusprofundi, but is occurring also in organisms from other haloarchaeal genera.
Highlights
IntroductionArchaeal flagella (archaella) are morphologically and functionally similar to bacterial flagella
Archaeal flagella are morphologically and functionally similar to bacterial flagella
Archaellar filaments consist of thousands of copies of the protein protomer archaellin
Summary
Archaeal flagella (archaella) are morphologically and functionally similar to bacterial flagella. The archaellum structure, assembly mechanism and protein composition is fundamentally different from the flagellum and instead shows similarity to type IV pili. The structure of archaeal filaments differs significantly from bacterial flagella, and from bacterial type IV pili (Braun et al, 2016; Poweleit et al, 2016). To explain the archaella supercoiling, it was proposed to consider them as semiflexible filaments in a viscous medium (Wolgemuth et al, 2000; Tony et al, 2006; Coq et al, 2008). For such structures, thrust can be generated by their rotation. The detailed mechanism of the archaellum supercoiling is not fully understood
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