Joined: May 2002
Jarrell and others have written a detailed review of prok. motility. Very useful article.
Microbiology 2003 Feb;149(Pt 2):295-304
Prokaryotic motility structures.
Bardy SL, Ng SY, Jarrell KF.
Department of Microbiology and Immunology, Queen's University, Kingston, ON, Canada K7L 3N6.
Prokaryotes use a wide variety of structures to facilitate motility. The majority of research to date has focused on swimming motility and the molecular architecture of the bacterial flagellum. While intriguing questions remain, especially concerning the specialized export system involved in flagellum assembly, for the most part the structural components and their location within the flagellum and function are now known. The same cannot be said of the other apparati including archaeal flagella, type IV pili, the junctional pore, ratchet structure and the contractile cytoskeleton used by a variety of organisms for motility. In these cases, many of the structural components have yet to be identified and the mechanism of action that results in motility is often still poorly understood. Research on the bacterial flagellum has greatly aided our understanding of not only motility but also protein secretion and genetic regulation systems. Continued study and understanding of all prokaryotic motility structures will provide a wealth of knowledge that is sure to extend beyond the bounds of prokaryotic movement.
PMID: 12624192 [PubMed - in process]
- They say the archaeal flagellum is powered by a proton gradient. This contradicts my earlier thought which was that it was ATP-powered. However, they cite no demonstration of the power source. I would keep the question in mind, but here is what they say:
"The other major subdivision of prokaryotes is the domain Archaea. Members are motile via a structure that appears to be fundamentally distinct from the bacterial counterpart in composition and, likely, assembly (Thomas et al., 2001). The archaeal flagellum is a rotary structure, driven by a proton gradient, and it is thinner than typical bacterial flagella."
- A more detailed review of spirochete flagella which are weird.
- A nice review of current knowledge on the archaeal flagellum proteins, several identified similarities/homologies to type IV pilins...
- The archaeal flagellum probably/usually has hook and filament proteins, and they find at least a bit of evidence that the difference between the two is not so great:
"In archaea, there are always multiple (2–6) flagellin genes present (Sulfolobus solfataricus appears to be an exception). Thus far the only components of the archaeal flagellum identified are the flagellins themselves, where it appears that the multiple flagellins are all present as structural components of the assembled flagellum. Recent work indicated that the hook protein might in fact be a minor flagellin, FlaB3 in the case of Methanococcus voltae (Bardy et al., 2002) (Fig. 4)."
- Type IV pili movies (twitching motility etc.):
Type IV pili movies
- Ratchet structure review; it would be nice to know the genes involved, particularly if there is any rotary motion involved...
- Here's a whole new kind of motility, the contractile cytoskeleton (in a prokaryote)
Spiroplasma melliferum is one of the smallest free-living organisms on earth with a genome size about half that of E. coli. Surprisingly, this bacterium is motile, though nonflagellated, and it lacks any genes analogous to ones involved in flagellation as well as known gliding genes. This organism lacks a cell wall but has a membrane-bound internal cytoskeleton, composed primarily of a unique 59 kDa protein, which is thought to act as a linear motor, in contrast to the rotary motor of the flagellum (Trachtenberg, 1998) (Fig. 9). The cytoskeleton is attached to the cytoplasmic membrane, possibly through one or more of the approximately seven proteins that co-purify with it. The cytoskeleton is involved in motility due to its linear contraction and its close interaction with the cytoplasmic membrane (Trachtenberg & Gilad, 2001). The cytoskeleton exists as a seven fibril ribbon that extends the length of the cell. A conformational switch in the monomer leads to length changes: because of the strong interconnectiveness of the cytoskeleton subunits, changes in any part of the fibril are transmitted to neighbours and ultimately to the attached membrane. Though poorly studied at present, this motility structure represents a truly novel approach to motility using what appears to be a much smaller complement of genes than that required for flagellation. Identification of the roles of the cytoskeleton co-purifying proteins will be a major advance in the elucidation of this motility structure."
Conclusion: not much on evolution but good overview review.
While motility is commonplace among the prokaryotes, it is important to note the variety of structures responsible for motility. These structures vary depending not only on the organism in question, but also on the particular environment. Study of the bacterial flagellum has provided insights into many aspects of prokaryotic cellular activities including genetics and regulation, physiology, environmental sensing, protein secretion and assembly of complex structures. Continued study of all prokaryotic motility structures will provide knowledge that is likely to reach far beyond the topic of motility.