Jump to content

Flagellum

From Wikipedia, the free encyclopedia

Flagellum
Structure ofbacterialflagellum
SEMimage of flagellatedeukaryoteChlamydomonassp. (10000×)
Identifiers
MeSHD005407
THH1.00.01.1.01032
FMA67472
Anatomical terminology

Aflagellum(/fləˈɛləm/;pl.:flagella) (Latinfor 'whip' or 'scourge') is a hairlike appendage that protrudes from certainplantand animalsperm cells,fromfungalspores(zoospores), and from a wide range ofmicroorganismsto providemotility.[1][2][3][4]Manyprotistswith flagella are known asflagellates.

A microorganism may have from one to many flagella. Agram-negative bacteriumHelicobacter pylori,for example, uses its flagella to propel itself through the stomach to reach themucus liningwhere it may colonise the epithelium and potentially cause gastritis, andulcers– a risk factor forstomach cancer.[5]In someswarming bacteria,the flagellum can also function as a sensoryorganelle,being sensitive to wetness outside the cell.[6]

Across thethree domainsofBacteria,Archaea,andEukaryota,the flagellum has a different structure, protein composition, and mechanism of propulsion but shares the same function of providing motility. TheLatinwordflagellummeans "whip"to describe its lash-like swimming motion. The flagellum in archaea is called thearchaellumto note its difference from the bacterial flagellum.[7][8]

Eukaryotic flagella andciliaare identical in structure but have different lengths and functions.[9]Prokaryoticfimbriaeandpiliare smaller, and thinner appendages, with different functions.

Types

[edit]
Prokaryotic(bacterial and archaeal) flagella run in a rotary movement, while eukaryotic flagella run in a bending movement. The prokaryotic flagellum uses arotary motor,and the eukaryotic flagellum uses a complex sliding filament system. Eukaryotic flagella are ATP-driven, while prokaryotic flagella can be ATP-driven (Archaea) or proton-driven (Bacteria).[10]

The three types of flagella are bacterial, archaeal, and eukaryotic.

The flagella in eukaryotes havedyneinandmicrotubulesthat move with a bending mechanism. Bacteria and archaea do not have dynein or microtubules in their flagella, and they move using a rotary mechanism.[11]

Other differences among these three types are:

  • Bacterial flagella are helical filaments, each with arotary motorat its base which can turn clockwise or counterclockwise.[12][13][14]They provide two of several kinds ofbacterial motility.[15][16]
  • Archaeal flagella (archaella) are superficially similar to bacterial flagella in that it also has a rotary motor, but are different in many details and considered non-homologous.[17][18][19]
  • Eukaryotic flagella—those of animal, plant, and protist cells—are complex cellular projections that lash back and forth. Eukaryotic flagella andmotile ciliaare identical in structure, but have different lengths, waveforms, and functions.Primary ciliaare immotile, and have astructurally different9+0 axonemerather than the9+2 axonemefound in both flagella and motile cilia.

Bacterial flagella

[edit]

Structure and composition

[edit]

The bacterial flagellum is made up ofproteinsubunits offlagellin.[11]Its shape is a 20-nanometer-thick hollow tube. It ishelicaland has a sharp bend just outside the outer membrane; this "hook" allows the axis of the helix to point directly away from the cell. A shaft runs between the hook and thebasal body,passing through protein rings in the cell's membrane that act as bearings.Gram-positiveorganisms have two of these basal body rings, one in thepeptidoglycanlayer and one in theplasma membrane.Gram-negativeorganisms have four such rings: theL ringassociates with thelipopolysaccharides,theP ringassociates withpeptidoglycanlayer, the M ring is embedded in theplasma membrane,and the S ring is directly attached to thecytoplasm.The filament ends with a capping protein.[20][21]

The flagellar filament is the long, helical screw that propels the bacterium when rotated by the motor, through the hook. In most bacteria that have been studied, including the gram-negativeEscherichia coli,Salmonella typhimurium,Caulobacter crescentus,andVibrio alginolyticus,the filament is made up of 11 protofilaments approximately parallel to the filament axis. Each protofilament is a series of tandem protein chains. However,Campylobacter jejunihas seven protofilaments.[22]

The basal body has several traits in common with some types ofsecretory pores,such as the hollow, rod-like "plug" in their centers extending out through the plasma membrane. The similarities between bacterial flagella and bacterial secretory system structures and proteins provide scientific evidence supporting the theory that bacterial flagella evolved from thetype-three secretion system(TTSS).

The atomic structure of both bacterial flagella as well as the TTSSinjectisomehave been elucidated in great detail, especially with the development ofcryo-electron microscopy.The best understood parts are the parts between the inner and outermembrane,that is, the scaffolding rings of the inner membrane (IM), the scaffolding pairs of the outer membrane (OM), and the rod/needle (injectisome) or rod/hook (flagellum) sections.[23]

Motor

[edit]
Bacterial flagellar motor assembly
Bacterial flagellar motor assembly: Shown here is the C-ring at the base with FliG in red, FliM in yellow, and FliN in shades of purple; the MS-ring in blue; the MotAB in brown; the LP-ring in pink; and the rod in gray.[24]

The bacterial flagellum is driven by a rotary engine (Mot complex) made up of protein, located at the flagellum's anchor point on the inner cell membrane. The engine is powered byproton-motive force,i.e., by the flow of protons (hydrogen ions) across the bacterial cell membrane due to aconcentration gradientset up by the cell's metabolism (Vibriospecies have two kinds of flagella, lateral and polar, and some are driven by a sodiumion pumprather than aproton pump[25]). The rotor transports protons across the membrane, and is turned in the process. The rotor alone can operate at 6,000 to 100,000rpm,[26]but with the flagellar filament attached usually only reaches 200 to 1000 rpm. The direction of rotation can be changed by theflagellar motor switchalmost instantaneously, caused by a slight change in the position of a protein,FliG,in the rotor.[27]The flagellum is highly energy efficient and uses very little energy.[28][unreliable source?]The torque is transferred from the MotAB to the torque helix on FliG's D5 domain and with the increase in the requirement of the torque or speed more MotAB are employed.[24]Because the flagellar motor has no on-off switch, the protein epsE is used as a mechanical clutch to disengage the motor from the rotor, thus stopping the flagellum and allowing the bacterium to remain in one place.[29]

The cylindrical shape of flagella is suited to locomotion of microscopic organisms; these organisms operate at a lowReynolds number,where the viscosity of the surrounding water is much more important than its mass or inertia.[30]

The rotational speed of flagella varies in response to the intensity of the proton-motive force, thereby permitting certain forms of speed control, and also permitting some types of bacteria to attain remarkable speeds in proportion to their size; some achieve roughly 60 cell lengths per second. At such a speed, a bacterium would take about 245 days to cover 1 km; although that may seem slow, the perspective changes when the concept of scale is introduced. In comparison to macroscopic life forms, it is very fast indeed when expressed in terms of number of body lengths per second. A cheetah, for example, only achieves about 25 body lengths per second.[31]

Through use of their flagella, bacteria are able to move rapidly towards attractants and away from repellents, by means of abiased random walk,withruns and tumblesbrought about by rotating its flagellumcounterclockwiseandclockwise,respectively. The two directions of rotation are not identical (with respect to flagellum movement) and are selected by a molecular switch.[32]Clockwise rotation is called thetraction modewith the body following the flagella. Counterclockwise rotation is called thethruster modewith the flagella lagging behind the body.[33]

Assembly

[edit]

During flagellar assembly, components of the flagellum pass through the hollow cores of the basal body and the nascent filament. During assembly, protein components are added at the flagellar tip rather than at the base.[34]In vitro,flagellar filaments assemble spontaneously in a solution containing purified flagellin as the sole protein.[35]

Evolution

[edit]

At least 10 protein components of the bacterial flagellum share homologous proteins with thetype three secretion system(T3SS) found in many gram-negative bacteria,[36]hence one likely evolved from the other. Because the T3SS has a similar number of components as a flagellar apparatus (about 25 proteins), which one evolved first is difficult to determine. However, the flagellar system appears to involve more proteins overall, including various regulators and chaperones, hence it has been argued that flagella evolved from a T3SS. However, it has also been suggested[37]that the flagellum may have evolved first or the two structures evolved in parallel. Early single-cell organisms' need formotility(mobility) support that the more mobile flagella would be selected by evolution first,[37]but the T3SS evolving from the flagellum can be seen as 'reductive evolution', and receives no topological support from thephylogenetictrees.[38]The hypothesis that the two structures evolved separately from a common ancestor accounts for the protein similarities between the two structures, as well as their functional diversity.[39]

Flagella and the intelligent design debate

[edit]

Some authors have argued that flagella cannot have evolved, assuming that they can only function properly when all proteins are in place. In other words, the flagellar apparatus is "irreducibly complex".[40]However, many proteins can be deleted or mutated and the flagellum still works, though sometimes at reduced efficiency.[41]Moreover, with many proteins unique to some number across species, diversity of bacterial flagella composition was higher than expected.[42]Hence, the flagellar apparatus is clearly very flexible in evolutionary terms and perfectly able to lose or gain protein components. For instance, a number of mutations have been found thatincreasethe motility ofE. coli.[43]Additional evidence for the evolution of bacterial flagella includes the existence of vestigial flagella, intermediate forms of flagella and patterns of similarities among flagellar protein sequences, including the observation that almost all of the core flagellar proteins have known homologies with non-flagellar proteins.[36]Furthermore, several processes have been identified as playing important roles in flagellar evolution, including self-assembly of simple repeating subunits, gene duplication with subsequent divergence, recruitment of elements from other systems ('molecular bricolage') and recombination.[44]

Flagellar arrangements

[edit]

Different species of bacteria have different numbers and arrangements of flagella,[45][46]named using the termtricho,from the Greektrichosmeaninghair.[47]

  • Monotrichousbacteria such asVibrio choleraehave a singlepolar flagellum.[48]
  • Amphitrichousbacteria have a single flagellum on each of two opposite ends (e.g.,Alcaligenes faecalis)—only one flagellum operates at a time, allowing the bacterium to reverse course rapidly by switching which flagellum is active.
  • Lophotrichousbacteria (lophoGreek combining term meaningcrestortuft)[49]have multiple flagella located at the same spot on the bacterial surface such asHelicobacter pylori,which act in concert to drive the bacteria in a single direction. In many cases, the bases of multiple flagella are surrounded by a specialized region of the cell membrane, called thepolar organelle.[citation needed]
  • Peritrichousbacteria have flagella projecting in all directions (e.g.,E. coli).

Counterclockwise rotation of a monotrichous polar flagellum pushes the cell forward with the flagellum trailing behind, much like a corkscrew moving inside cork. Water on the microscopic scale is highlyviscous,unlike usualwater.

Spirochetes,in contrast, have flagella calledendoflagellaarising from opposite poles of the cell, and are located within theperiplasmic spaceas shown by breaking the outer-membrane and also byelectron cryotomographymicroscopy.[50]The rotation of the filaments relative to the cell body causes the entire bacterium to move forward in a corkscrew-like motion, even through material viscous enough to prevent the passage of normally flagellated bacteria.

In certain large forms ofSelenomonas,more than 30 individual flagella are organized outside the cell body, helically twining about each other to form a thick structure (easily visible with the light microscope) called a "fascicle".

In someVibriospp. (particularlyVibrio parahaemolyticus[51]) and relatedbacteriasuch asAeromonas,two flagellar systems co-exist, using different sets of genes and different ion gradients for energy. The polar flagella are constitutively expressed and provide motility in bulk fluid, while the lateral flagella are expressed when the polar flagella meet too much resistance to turn.[52][53][54][55][56][57]These provide swarming motility on surfaces or in viscous fluids.

Bundling
[edit]

Bundling is an event that can happen in multi-flagellated cells, bundling the flagella together and causing them to rotate in a coordinated manner.

Flagella are left-handed helices, and when rotated counter-clockwise by their rotors, they can bundle and rotate together. When the rotors reverse direction, thus rotating clockwise, the flagellum unwinds from the bundle. This may cause the cell to stop its forward motion and instead start twitching in place, referred to astumbling.Tumbling results in a stochastic reorientation of the cell, causing it to change the direction of its forward swimming.

It is not known which stimuli drive the switch between bundling and tumbling, but the motor is highly adaptive to different signals. In the model describingchemotaxis( "movement on purpose" ) the clockwise rotation of a flagellum is suppressed by chemical compounds favorable to the cell (e.g. food). When moving in a favorable direction, the concentration of such chemical attractants increases and therefore tumbles are continually suppressed, allowing forward motion; likewise, when the cell's direction of motion is unfavorable (e.g., away from a chemical attractant), tumbles are no longer suppressed and occur much more often, with the chance that the cell will be thus reoriented in the correct direction.

Even if all flagella would rotate clockwise, however, they often cannot form a bundle due to geometrical and hydrodynamic reasons.[58][59]

Eukaryotic flagella

[edit]
Eukaryotic flagella. 1–axoneme, 2–cell membrane, 3–IFT (IntraFlagellar Transport), 4–Basal body, 5–Cross section of flagella, 6–Triplets of microtubules of basal body
Cross section of anaxoneme
Longitudinal section through the flagella area inChlamydomonas reinhardtii.In the cell apex is the basal body that is the anchoring site for a flagellum. Basal bodies originate from and have a substructure similar to that of centrioles, with nine peripheral microtubule triplets (see structure at bottom center of image).
The "9+2" structure is visible in this cross-section micrograph of an axoneme.

Terminology

[edit]

Aiming to emphasize the distinction between the bacterial flagella and the eukaryotic cilia and flagella, some authors attempted to replace the name of these two eukaryotic structures with "undulipodia"(e.g., all papers byMargulissince the 1970s)[60]or "cilia" for both (e.g., Hülsmann, 1992;[61]Adl et al., 2012;[62]most papers ofCavalier-Smith), preserving "flagella" for the bacterial structure. However, the discriminative usage of the terms "cilia" and "flagella" for eukaryotes adopted in this article (see§ Flagella versus ciliabelow) is still common (e.g., Andersen et al., 1991;[63]Leadbeater et al., 2000).[64]

Internal structure

[edit]

The core of a eukaryotic flagellum, known as theaxonemeis a bundle of nine fused pairs ofmicrotubulesknown asdoubletssurrounding two central single microtubules (singlets). This9+2 axonemeis characteristic of the eukaryotic flagellum. At the base of a eukaryotic flagellum is abasal body,"blepharoplast" or kinetosome, which is themicrotubule organizing centerfor flagellar microtubules and is about 500 nanometers long. Basal bodies are structurally identical tocentrioles.The flagellum is encased within the cell'splasma membrane,so that the interior of the flagellum is accessible to the cell'scytoplasm.

Besides the axoneme and basal body, relatively constant in morphology, other internal structures of the flagellar apparatus are the transition zone (where the axoneme and basal body meet) and the root system (microtubular or fibrilar structures that extend from the basal bodies into the cytoplasm), more variable and useful as indicators of phylogenetic relationships of eukaryotes. Other structures, more uncommon, are the paraflagellar (or paraxial, paraxonemal) rod, the R fiber, and the S fiber.[65]: 63–84 For surface structures, see below.

Mechanism

[edit]

Each of the outer 9 doublet microtubules extends a pair ofdyneinarms (an "inner" and an "outer" arm) to the adjacent microtubule; these produce force through ATP hydrolysis. The flagellar axoneme also containsradial spokes,polypeptide complexes extending from each of the outer nine microtubule doublets towards the central pair, with the "head" of the spoke facing inwards. The radial spoke is thought to be involved in the regulation of flagellar motion, although its exact function and method of action are not yet understood.[66]

Flagella versus cilia

[edit]
Beating pattern of eukaryotic "flagellum" and "cillum", a traditional distinction before the structures of the two are known.

The regular beat patterns of eukaryoticciliaand flagella generate motion on a cellular level. Examples range from the propulsion of single cells such as the swimming ofspermatozoato the transport of fluid along a stationary layer of cells such as in therespiratory tract.[67]

Although eukaryoticciliaand flagella are ultimately the same, they are sometimes classed by their pattern of movement, a tradition from before their structures have been known. In the case of flagella, the motion is often planar and wave-like, whereas the motile cilia often perform a more complicated three-dimensional motion with a power and recovery stroke.[67]Yet another traditional form of distinction is by the number of 9+2 organelles on the cell.[66]

Intraflagellar transport

[edit]

Intraflagellar transport,the process by which axonemal subunits,transmembrane receptors,and other proteins are moved up and down the length of the flagellum, is essential for proper functioning of the flagellum, in both motility and signal transduction.[68]

Evolution and occurrence

[edit]

Eukaryotic flagella or cilia, probably an ancestral characteristic,[69]are widespread in almost all groups of eukaryotes, as a relatively perennial condition, or as a flagellated life cycle stage (e.g.,zoids,gametes,zoospores,which may be produced continually or not).[70][71][62]

The first situation is found either in specialized cells of multicellular organisms (e.g., thechoanocytesofsponges,or the ciliatedepitheliaofmetazoans), as inciliatesand many eukaryotes with a "flagellate condition" (or "monadoidlevel of organization",seeFlagellata,an artificial group).

Flagellated lifecycle stages are found in many groups, e.g., manygreen algae(zoospores and male gametes),bryophytes(male gametes),pteridophytes(male gametes), somegymnosperms(cycadsandGinkgo,as male gametes), centricdiatoms(male gametes),brown algae(zoospores and gametes),oomycetes(assexual zoospores and gametes),hyphochytrids(zoospores),labyrinthulomycetes(zoospores), someapicomplexans(gametes), someradiolarians(probably gametes),[72]foraminiferans(gametes),plasmodiophoromycetes(zoospores and gametes),myxogastrids(zoospores),metazoans(male gametes), andchytridfungi (zoospores and gametes).

Flagella or cilia are completely absent in some groups, probably due to a loss rather than being a primitive condition. The loss of cilia occurred inred algae,some green algae (Zygnematophyceae), thegymnospermsexcept cycads andGinkgo,angiosperms,pennatediatoms,someapicomplexans,someamoebozoans,in the sperm of somemetazoans,[73]and infungi(exceptchytrids).

Typology

[edit]

A number of terms related to flagella or cilia are used to characterize eukaryotes.[71][74][65]: 60–63 [75][76]According to surface structures present, flagella may be:

  • whiplash flagella (= smooth, acronematic flagella): without hairs, e.g., inOpisthokonta
  • hairy flagella (= tinsel, flimmer, pleuronematic flagella): with hairs (=mastigonemessensu lato), divided in:
  • stichonematic flagella: with a single row of hairs
  • pantonematic flagella: with two rows of hairs
  • acronematic: flagella with a single, terminal mastigoneme or flagellar hair (e.g.,bodonids);[77]some authors use the term as synonym of whiplash
  • with scales: e.g.,Prasinophyceae
  • with spines: e.g., somebrown algae
  • with undulating membrane: e.g., somekinetoplastids,someparabasalids
  • with proboscis (trunk-like protrusion of the cell): e.g.,apusomonads,somebodonids[78]

According to the number of flagella, cells may be: (remembering that some authors use "ciliated" instead of "flagellated" )[62][79]

According to the place of insertion of the flagella:[80]

  • opisthokont: cells with flagella inserted posteriorly, e.g., inOpisthokonta(Vischer, 1945). InHaptophyceae,flagella are laterally to terminally inserted, but are directed posteriorly during rapid swimming.[81]
  • akrokont: cells with flagella inserted apically
  • subakrokont: cells with flagella inserted subapically
  • pleurokont: cells with flagella inserted laterally

According to the beating pattern:

  • gliding: a flagellum that trails on the substrate[78]
  • heterodynamic: flagella with different beating patterns (usually with one flagellum functioning in food capture and the other functioning in gliding, anchorage, propulsion or "steering" )[82]
  • isodynamic: flagella beating with the same patterns

Other terms related to the flagellar type:

  • isokont: cells with flagella of equal length. It was also formerly used to refer to theChlorophyta
  • anisokont: cells with flagella of unequal length, e.g., someEuglenophyceaeandPrasinophyceae
  • heterokont: term introduced by Luther (1899) to refer to theXanthophyceae,due to the pair of flagella of unequal length. It has taken on a specific meaning in referring to cells with an anterior straminipilous flagellum (with tripartite mastigonemes, in one or two rows) and a posterior usually smooth flagellum. It is also used to refer to the taxonHeterokonta
  • stephanokont: cells with a crown of flagella near its anterior end, e.g., the gametes and spores ofOedogoniales,the spores of someBryopsidales.Term introduced by Blackman & Tansley (1902) to refer to theOedogoniales
  • akont: cells without flagella. It was also used to refer to taxonomic groups, as Aconta or Akonta: theZygnematophyceaeandBacillariophyceae(Oltmanns, 1904), or theRhodophyceae(Christensen, 1962)

Archaeal flagella

[edit]

Thearchaellumpossessed by some species ofArchaeais superficially similar to the bacterial flagellum; in the 1980s, they were thought to be homologous on the basis of gross morphology and behavior.[83]Both flagella and archaella consist of filaments extending outside the cell, and rotate to propel the cell. Archaeal flagella have a unique structure which lacks a central channel. Similar to bacterialtype IV pilins,the archaeal proteins (archaellins) are made with class 3 signal peptides and they are processed by a type IV prepilin peptidase-like enzyme. The archaellins are typically modified by the addition of N-linkedglycanswhich are necessary for proper assembly or function.[3]

Discoveries in the 1990s revealed numerous detailed differences between the archaeal and bacterial flagella. These include:

  • Bacterial flagella rotation is powered by theproton motive force– a flow ofH+ionsor occasionally by thesodium-motive force– a flow ofNa+ions; archaeal flagella rotation is powered byATP.[84]
  • 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.
  • Bacterial flagella are thicker than archaella, and the bacterial filament has a large enough hollow "tube" inside that the flagellin subunits can flow up the inside of the filament and get added at the tip; the archaellum is too thin (12-15 nm) to allow this.[85]
  • Many components of bacterial flagella share sequence similarity to components of thetype III secretion systems,but the components of bacterial flagella and archaella share no sequence similarity. Instead, some components of archaella share sequence and morphological similarity with components oftype IV pili,which are assembled through the action oftype II secretion systems(the nomenclature of pili and protein secretion systems is not consistent).[85]

These differences support the theory that the bacterial flagella and archaella are a classic case of biologicalanalogy,orconvergent evolution,rather thanhomology.[86][87][88]Research into the structure of archaella made significant progress beginning in the early 2010s, with the first atomic resolution structure of an archaella protein, the discovery of additional functions of archaella, and the first reports of archaella in Nanoarchaeota and Thaumarchaeota.[89][90]

Fungal

[edit]

The onlyfungito have a single flagellum on theirsporesare thechytrids.InBatrachochytrium dendrobatidisthe flagellum is 19–20 μm long.[91]A nonfunctioningcentriolelies adjacent to thekinetosome.Nine interconnected props attach the kinetosome to theplasmalemma,and a terminal plate is present in the transitional zone. An inner ring-like structure attached to the tubules of the flagellar doublets within the transitional zone has been observed in transverse section.[91]

Additional images

[edit]

See also

[edit]

References

[edit]
  1. ^Bardy, Sonia L.; Ng, Sandy Y. M.; Jarrell, Ken F. (1 February 2003)."Prokaryotic motility structures".Microbiology.149(2): 295–304.doi:10.1099/mic.0.25948-0.PMID12624192.
  2. ^Silflow, Carolyn D.; Lefebvre, Paul A. (1 December 2001)."Assembly and Motility of Eukaryotic Cilia and Flagella. Lessons from Chlamydomonas reinhardtii".Plant Physiology.127(4): 1500–1507.doi:10.1104/pp.010807.PMC1540183.PMID11743094.
  3. ^abJarrell, Ken F., ed. (2009).Pili and flagella: current research and future trends.Norfolk: Caister academic press.ISBN978-1-904455-48-6.
  4. ^Malo, Aurelio F; Gomendio, Montserrat; Garde, Julian; Lang-Lenton, Barbara; Soler, Ana J; Roldan, Eduardo R.S (22 June 2006)."Sperm design and sperm function".Biology Letters.2(2): 246–249.doi:10.1098/rsbl.2006.0449.PMC1618917.PMID17148374.
  5. ^Lacy, BE; Rosemore, J (October 2001)."Helicobacter pylori: ulcers and more: the beginning of an era".The Journal of Nutrition.131(10): 2789S–2793S.doi:10.1093/jn/131.10.2789S.PMID11584108.Archived fromthe original(abstract page)on 7 February 2009.Retrieved2 June2008.
  6. ^Wang, Qingfeng; Suzuki, Asaka; Mariconda, Susana; Porwollik, Steffen; Harshey, Rasika M (1 June 2005)."Sensing wetness: a new role for the bacterial flagellum".The EMBO Journal.24(11): 2034–2042.doi:10.1038/sj.emboj.7600668.PMC1142604.PMID15889148.
  7. ^Albers, Sonja-Verena; Jarrell, Ken F. (27 January 2015)."The archaellum: how archaea swim".Frontiers in Microbiology.6:23.doi:10.3389/fmicb.2015.00023.PMC4307647.PMID25699024.
  8. ^Quax, TEF; Albers, SV; Pfeiffer, F (14 December 2018)."Taxis in archaea".Emerging Topics in Life Sciences.2(4): 535–546.doi:10.1042/ETLS20180089.PMC7289035.PMID33525831.
  9. ^Haimo, L T; Rosenbaum, J L (1 December 1981)."Cilia, flagella, and microtubules".The Journal of Cell Biology.91(3): 125s–130s.doi:10.1083/jcb.91.3.125s.PMC2112827.PMID6459327.
  10. ^Streif, Stefan; Staudinger, Wilfried Franz; Marwan, Wolfgang; Oesterhelt, Dieter (December 2008). "Flagellar Rotation in the Archaeon Halobacterium salinarum Depends on ATP".Journal of Molecular Biology.384(1): 1–8.doi:10.1016/j.jmb.2008.08.057.PMID18786541.
  11. ^abAlberts, Bruce (2015).Molecular biology of the cell(Sixth ed.). New York, NY. p. 942.ISBN9780815344643.{{cite book}}:CS1 maint: location missing publisher (link)
  12. ^Silverman, Michael; Simon, Melvin (May 1974). "Flagellar rotation and the mechanism of bacterial motility".Nature.249(5452): 73–74.Bibcode:1974Natur.249...73S.doi:10.1038/249073a0.PMID4598030.S2CID10370084.
  13. ^Lowe, Graeme; Meister, Markus; Berg, Howard C. (February 1987). "Rapid rotation of flagellar bundles in swimming bacteria".Nature.325(6105): 637–640.Bibcode:1987Natur.325..637L.doi:10.1038/325637a0.S2CID4242129.
  14. ^Berg, Howard C.; Anderson, Robert A. (October 1973). "Bacteria Swim by Rotating their Flagellar Filaments".Nature.245(5425): 380–382.Bibcode:1973Natur.245..380B.doi:10.1038/245380a0.PMID4593496.S2CID4173914.
  15. ^Jahn, T L; Bovee, E C (October 1965). "Movement and Locomotion of Microorganisms".Annual Review of Microbiology.19(1): 21–58.doi:10.1146/annurev.mi.19.100165.000321.PMID5318439.
  16. ^Harshey, RM (2003). "Bacterial motility on a surface: many ways to a common goal".Annual Review of Microbiology.57:249–73.doi:10.1146/annurev.micro.57.030502.091014.PMID14527279.
  17. ^Ng, Sandy Y.M.; Chaban, Bonnie; Jarrell, Ken F. (2006). "Archaeal Flagella, Bacterial Flagella and Type IV Pili: A Comparison of Genes and Posttranslational Modifications".Microbial Physiology.11(3–5): 167–191.doi:10.1159/000094053.PMID16983194.S2CID30386932.
  18. ^Metlina, A. L. (November 2004). "Bacterial and archaeal flagella as prokaryotic motility organelles".Biochemistry (Moscow).69(11): 1203–1212.doi:10.1007/s10541-005-0065-8.PMID15627373.S2CID632440.
  19. ^Jarrell, K (2009). "Archaeal Flagella and Pili".Pili and Flagella: Current Research and Future Trends.Caister Academic Press.ISBN978-1-904455-48-6.
  20. ^Macnab, Robert M. (October 2003). "How Bacteria Assemble Flagella".Annual Review of Microbiology.57(1): 77–100.doi:10.1146/annurev.micro.57.030502.090832.PMID12730325.
  21. ^Diószeghy, Zoltán; Závodszky, Péter; Namba, Keiichi; Vonderviszt, Ferenc (18 June 2004). "Stabilization of flagellar filaments by HAP2 capping".FEBS Letters.568(1–3): 105–109.Bibcode:2004FEBSL.568..105D.doi:10.1016/j.febslet.2004.05.029.PMID15196929.S2CID33886010.
  22. ^Galkin, Vitold E.; Yu, Xiong; Bielnicki, Jakub; Heuser, John; Ewing, Cheryl P.; Guerry, Patricia; Egelman, Edward H. (18 April 2008). "Divergence of Quaternary Structures Among Bacterial Flagellar Filaments".Science.320(5874): 382–385.Bibcode:2008Sci...320..382G.doi:10.1126/science.1155307.PMID18420936.S2CID7702002.
  23. ^Worrall, Liam J.; Majewski, Dorothy D.; Strynadka, Natalie C.J. (15 September 2023)."Structural Insights into Type III Secretion Systems of the Bacterial Flagellum and Injectisome".Annual Review of Microbiology.77(1): 669–698.doi:10.1146/annurev-micro-032521-025503.ISSN0066-4227.PMID37713458.S2CID261963968.
  24. ^abSingh, Prashant K.; Sharma, Pankaj; Afanzar, Oshri; Goldfarb, Margo H.; Maklashina, Elena; Eisenbach, Michael; Cecchini, Gary; Iverson, T. M. (17 April 2024)."CryoEM structures reveal how the bacterial flagellum rotates and switches direction".Nature Microbiology.9(5): 1271–1281.doi:10.1038/s41564-024-01674-1.ISSN2058-5276.PMC11087270.PMID38632342.
  25. ^Atsumi, Tatsuo; McCartert, Linda; Imae, Yasuo (January 1992). "Polar and lateral flagellar motors of marine Vibrio are driven by different ion-motive forces".Nature.355(6356): 182–184.Bibcode:1992Natur.355..182A.doi:10.1038/355182a0.PMID1309599.S2CID4315167.
  26. ^Kojima, Seiji; Blair, David F (2004),"The Bacterial Flagellar Motor: Structure and Function of a Complex Molecular Machine",International Review of Cytology,233,Elsevier: 93–134,doi:10.1016/s0074-7696(04)33003-2,ISBN978-0-12-364637-8,PMID15037363,retrieved23 April2024
  27. ^Dean, Tim (2 August 2010)."Inside nature's most efficient motor: the flagellar".Australian Life Scientist.
  28. ^Nagata, Yoshio (June 2014)."Unlocking the secrets of nature's nanomotor".Nikkei Asian Review.
  29. ^Whitfield, John (19 June 2008)."Bacterial engines have their own clutch".Nature News:news.2008.903.doi:10.1038/news.2008.903.Retrieved17 May2017.
  30. ^Dusenbery, DB (2009). "Chapter 13".Living at Micro Scale: The Unexpected Physics of Being Small.Cambridge: Harvard University Press.ISBN978-0-674-03116-6.
  31. ^Hildebrand, Milton (November 1959). "Motions of the running Cheetah and Horse".Journal of Mammalogy.44(4): 481–495.doi:10.2307/1376265.JSTOR1376265.Although according toHunter, Luke; Hamman, Dave (2003).Cheetah.Struik Publishers. pp. 37–38.the cheetah's fastest recorded speed was 110 km/h (68 mph)
  32. ^Meadows, Robin (10 May 2011)."How Bacteria Shift Gears".PLOS Biology.9(5): e1001061.doi:10.1371/journal.pbio.1001061.PMC3091840.PMID21572986.
  33. ^Sun, Qifang; Yuan, Chengzhi; Zhou, Sainan; Lu, Jing; Zeng, Meiyan; Cai, Xiong; Song, Houpan (19 October 2023)."Helicobacter pylori infection: a dynamic process from diagnosis to treatment".Frontiers in Cellular and Infection Microbiology.13.doi:10.3389/fcimb.2023.1257817.PMC10621068.PMID37928189.
  34. ^Minamino, Tohru; Imada, Katsumi; Namba, Keiichi (2008). "Mechanisms of type III protein export for bacterial flagellar assembly".Molecular BioSystems.4(11): 1105–1115.doi:10.1039/b808065h.PMID18931786.
  35. ^Asakura, Sho; Eguchi, Goro; Iino, Tetsuo (October 1964). "Reconstitution of bacterial flagella in vitro".Journal of Molecular Biology.10(1): 42–IN9.doi:10.1016/S0022-2836(64)80026-7.PMID14222895.
  36. ^abPallen, Mark J.; Matzke, Nicholas J. (October 2006). "From The Origin of Species to the origin of bacterial flagella".Nature Reviews Microbiology.4(10): 784–790.doi:10.1038/nrmicro1493.PMID16953248.S2CID24057949.
  37. ^abSaier, M (March 2004). "Evolution of bacterial type III protein secretion systems".Trends in Microbiology.12(3): 113–115.doi:10.1016/j.tim.2004.01.003.PMID15001186.
  38. ^Gophna, Uri; Ron, Eliora Z.; Graur, Dan (July 2003). "Bacterial type III secretion systems are ancient and evolved by multiple horizontal-transfer events".Gene.312:151–163.doi:10.1016/S0378-1119(03)00612-7.PMID12909351.
  39. ^McCann, Honour C.; Guttman, David S. (January 2008)."Evolution of the type III secretion system and its effectors in plant–microbe interactions".New Phytologist.177(1): 33–47.doi:10.1111/J.1469-8137.2007.02293.X.PMID18078471.
  40. ^Behe, Michael J. (2007).The edge of evolution: the search for the limits of Darwinism.New York, NY: Free Press.ISBN978-0-7432-9620-5.
  41. ^Rajagopala, Seesandra V; Titz, Björn; Goll, Johannes; Parrish, Jodi R; Wohlbold, Katrin; McKevitt, Matthew T; Palzkill, Timothy; Mori, Hirotada; Finley, Russell L; Uetz, Peter (January 2007)."The protein network of bacterial motility".Molecular Systems Biology.3(1): 128.doi:10.1038/msb4100166.PMC1943423.PMID17667950.
  42. ^Titz, Björn; Rajagopala, Seesandra V.; Ester, Claudia; Häuser, Roman; Uetz, Peter (November 2006)."Novel Conserved Assembly Factor of the Bacterial Flagellum".Journal of Bacteriology.188(21): 7700–7706.doi:10.1128/JB.00820-06.PMC1636259.PMID16936039.
  43. ^Kakkanat, Asha; Phan, Minh-Duy; Lo, Alvin W.; Beatson, Scott A.; Schembri, Mark A. (10 May 2017)."Novel genes associated with enhanced motility of Escherichia coli ST131".PLOS ONE.12(5): e0176290.Bibcode:2017PLoSO..1276290K.doi:10.1371/journal.pone.0176290.PMC5425062.PMID28489862.
  44. ^Pallen, M.J.; Gophna, U. (2007). "Bacterial Flagella and Type III Secretion: Case Studies in the Evolution of Complexity".Genome Dynamics.3:30–47.doi:10.1159/000107602.ISBN978-3-8055-8340-4.PMID18753783.
  45. ^"Bacterial flagella"(PDF).Archived(PDF)from the original on 9 October 2022.Retrieved29 December2021.
  46. ^Ruan, Juanfang; Kato, Takayuki; Santini, Claire-Lise; Miyata, Tomoko; Kawamoto, Akihiro; Zhang, Wei-Jia; Bernadac, Alain; Wu, Long-Fei; Namba, Keiichi (11 December 2012)."Architecture of a flagellar apparatus in the fast-swimming magnetotactic bacterium MO-1".Proceedings of the National Academy of Sciences.109(50): 20643–20648.Bibcode:2012PNAS..10920643R.doi:10.1073/pnas.1215274109.PMC3528567.PMID23184985.
  47. ^"tricho- prefix".Retrieved26 March2022.
  48. ^Echazarreta, MA; Klose, KE (2019)."VibrioFlagellar Synthesis ".Frontiers in Cellular and Infection Microbiology.9:131.doi:10.3389/fcimb.2019.00131.PMC6504787.PMID31119103.
  49. ^"Lopho".Retrieved26 March2022.
  50. ^Kudryashev, Mikhail; Cyrklaff, Marek; Baumeister, Wolfgang; Simon, Markus M.; Wallich, Reinhard; Frischknecht, Friedrich (March 2009)."Comparative cryo-electron tomography of pathogenic Lyme disease spirochetes".Molecular Microbiology.71(6): 1415–1434.doi:10.1111/j.1365-2958.2009.06613.x.PMID19210619.S2CID19650892.
  51. ^Kim, Yun-Kyeong; McCarter, Linda L. (July 2000)."Analysis of the Polar Flagellar Gene System of Vibrio parahaemolyticus".Journal of Bacteriology.182(13): 3693–3704.doi:10.1128/JB.182.13.3693-3704.2000.PMC94540.PMID10850984.
  52. ^Atsumi, T; Maekawa, Y; Yamada, T; Kawagishi, I; Imae, Y; Homma, M (August 1996)."Effect of viscosity on swimming by the lateral and polar flagella of Vibrio alginolyticus".Journal of Bacteriology.178(16): 5024–5026.doi:10.1128/jb.178.16.5024-5026.1996.PMC178290.PMID8759871.
  53. ^McCarter, Linda L. (2004). "Dual Flagellar Systems Enable Motility under Different Circumstances".Microbial Physiology.7(1–2): 18–29.doi:10.1159/000077866.PMID15170400.S2CID21963003.
  54. ^Merino, Susana; Shaw, Jonathan G.; Tomás, Juan M. (October 2006)."Bacterial lateral flagella: an inducible flagella system".FEMS Microbiology Letters.263(2): 127–135.doi:10.1111/j.1574-6968.2006.00403.x.PMID16978346.
  55. ^Belas, R; Simon, M; Silverman, M (July 1986)."Regulation of lateral flagella gene transcription in Vibrio parahaemolyticus".Journal of Bacteriology.167(1): 210–218.doi:10.1128/jb.167.1.210-218.1986.PMC212863.PMID3013835.
  56. ^Canals, Rocío; Altarriba, Maria; Vilches, Silvia; Horsburgh, Gavin; Shaw, Jonathan G.; Tomás, Juan M.; Merino, Susana (February 2006)."Analysis of the Lateral Flagellar Gene System of Aeromonas hydrophila AH-3".Journal of Bacteriology.188(3): 852–862.doi:10.1128/JB.188.3.852-862.2006.PMC1347325.PMID16428388.
  57. ^Canals, Rocío; Ramirez, Silvia; Vilches, Silvia; Horsburgh, Gavin; Shaw, Jonathan G.; Tomás, Juan M.; Merino, Susana (15 January 2006)."Polar Flagellum Biogenesis in Aeromonas hydrophila".Journal of Bacteriology.188(2): 542–555.doi:10.1128/JB.188.2.542-555.2006.PMC1347287.PMID16385045.
  58. ^Kim, MunJu; Bird, James C.; Van Parys, Annemarie J.; Breuer, Kenneth S.; Powers, Thomas R. (23 December 2003)."A macroscopic scale model of bacterial flagellar bundling".Proceedings of the National Academy of Sciences.100(26): 15481–15485.arXiv:cond-mat/0312562.Bibcode:2003PNAS..10015481K.doi:10.1073/pnas.2633596100.PMC307593.PMID14671319.
  59. ^Macnab, RM (January 1977)."Bacterial flagella rotating in bundles: a study in helical geometry".Proceedings of the National Academy of Sciences of the United States of America.74(1): 221–5.Bibcode:1977PNAS...74..221M.doi:10.1073/pnas.74.1.221.PMC393230.PMID264676.
  60. ^Taylor, F J R Max (1 November 2003)."The collapse of the two-kingdom system, the rise of protistology and the founding of the International Society for Evolutionary Protistology (ISEP)".International Journal of Systematic and Evolutionary Microbiology.53(6): 1707–1714.doi:10.1099/ijs.0.02587-0.PMID14657097.
  61. ^Hülsmann, Norbert (August 1992). "Undulipodium: End of a useless discussion".European Journal of Protistology.28(3): 253–257.doi:10.1016/s0932-4739(11)80231-2.PMID23195228.
  62. ^abcAdl, Sina M.; Simpson, Alastair G. B.; Lane, Christopher E.; Lukeš, Julius; Bass, David; Bowser, Samuel S.; Brown, Matthew W.; Burki, Fabien; Dunthorn, Micah; Hampl, Vladimir; Heiss, Aaron; Hoppenrath, Mona; Lara, Enrique; le Gall, Line; Lynn, Denis H.; McManus, Hilary; Mitchell, Edward A. D.; Mozley-Stanridge, Sharon E.; Parfrey, Laura W.; Pawlowski, Jan; Rueckert, Sonja; Shadwick, Laura; Schoch, Conrad L.; Smirnov, Alexey; Spiegel, Frederick W. (September 2012)."The Revised Classification of Eukaryotes".Journal of Eukaryotic Microbiology.59(5): 429–514.doi:10.1111/j.1550-7408.2012.00644.x.PMC3483872.PMID23020233.
  63. ^Andersen, R. A.; Barr, D. J. S.; Lynn, D. H.; Melkonian, M.; Moestrup, Ø.; Sleigh, M. A. (February 1991). "Terminology and nomenclature of the cytoskeletal elements associated with the flagellar/ciliary apparatus in protists".Protoplasma.164(1–3): 1–8.doi:10.1007/bf01320809.S2CID40755371.
  64. ^Leadbeater, Barry S. C.; Green, John C., eds. (2000).Flagellates: Unity, Diversity and Evolution.The Systematics Association Special Volume. Vol. 59. Taylor and Francis.ISBN978-1-4822-6822-5.
  65. ^abBarsanti, Laura; Gualtieri, Paolo (2006).Algae: Anatomy, Biochemistry, and Biotechnology.Florida, USA: CRC Press.ISBN9780203492598.
  66. ^abLindemann, CB; Lesich, KA (15 February 2010). "Flagellar and ciliary beating: the proven and the possible".Journal of Cell Science.123(Pt 4): 519–28.doi:10.1242/jcs.051326.PMID20145000.S2CID18673550.
  67. ^abLodish, Harvey; Berk, Arnold; Zipursky, S. Lawrence; Matsudaira, Paul; Baltimore, David; Darnell, James (2000). "Section 19.4Cilia and Flagella: Structure and Movement".Cilia and Flagella: Structure and Movement.ISBN0-7167-3136-3.
  68. ^Pazour, Gregory J. (October 2004)."Intraflagellar Transport and Cilia-Dependent Renal Disease: The Ciliary Hypothesis of Polycystic Kidney Disease".Journal of the American Society of Nephrology.15(10): 2528–2536.doi:10.1097/01.ASN.0000141055.57643.E0.PMID15466257.
  69. ^Yubuki, Naoji; Leander, Brian S. (July 2013)."Evolution of microtubule organizing centers across the tree of eukaryotes".The Plant Journal.75(2): 230–244.doi:10.1111/tpj.12145.PMID23398214.
  70. ^Raven, J.A. (2000)."The flagellate condition".Leadbeater & Green 2000,pp. 27–48.CRC Press.ISBN9781482268225.
  71. ^abWebster, John; Weber, Roland (25 January 2007)."Spores of Fungi".2007(3rd ed.). Cambridge: Cambridge University Press. pp. 23–24.ISBN9781139461504.
  72. ^Lahr, Daniel J. G.; Parfrey, Laura Wegener; Mitchell, Edward A. D.; Katz, Laura A.; Lara, Enrique (22 July 2011)."The chastity of amoebae: re-evaluating evidence for sex in amoeboid organisms".Proceedings of the Royal Society B: Biological Sciences.278(1715): 2081–2090.doi:10.1098/rspb.2011.0289.PMC3107637.PMID21429931.
  73. ^abAustin, CR (1995). Grudzinskas, Jurgis Gediminas; Yovich, J L (eds.).Gametes - the spermatozoon.Cambridge: Cambridge University Press.ISBN9780521479967.
  74. ^South, GR; Whittick, A (1987).Introduction to Phycology.Oxford: Blackwell Scientific Publications. p. 65.ISBN9781444314205.
  75. ^Dodge, JD (1973).The Fine Structure of Algal Cells.London: Academic Press. pp. 57–79.ISBN9780323158237.
  76. ^Lee, RE (2008).Phycology(4th ed.). Cambridge University Press. p.7.ISBN9781139469876.lee tubular hairs.
  77. ^Corliss, J.O.; Lom, J (2000). "An annotated glossary of protozoological terms". In Lee, J.J.; Leedale, G.F.; Bradbury, P. (eds.).An illustrated guide to the protozoa.Vol. 2 (2nd ed.). Society of Protozoologists. pp. 1346–85.ISBN1891276239.
  78. ^abJeuck, Alexandra; Arndt, Hartmut (November 2013)."A Short Guide to Common Heterotrophic Flagellates of Freshwater Habitats Based on the Morphology of Living Organisms".Protist.164(6): 842–860.doi:10.1016/j.protis.2013.08.003.PMID24239731.
  79. ^Sleigh, M (1989).Protozoa and other Protists.London: Edward Arnold. pp. 98–99.ISBN9780521428057.
  80. ^Sparrow, FK (1960).Aquatic phycomycetes(2nd ed.). Ann Arbor: Michigan: University of Michigan Press. p.15.
  81. ^Hibberd, DJ (1976). "The ultrastructure and taxonomy of the Chrysophyceae and Prymnesiophyceae (Haptophyceae): a survey with some new observations on the ultrastructure of the Chrysophyceae".Journal of the Linnean Society of London, Botany.72(2): 55–80.doi:10.1111/j.1095-8339.1976.tb01352.x.
  82. ^Sleigh, MA (1985)."Origin and evolution of flagellar movement".Cell Motil.5:137–138. Archived fromthe originalon 3 March 2016.Retrieved21 February2016.
  83. ^Cavalier-Smith, T (1987)."The origin of eukaryotic and archaebacterial cells".Annals of the New York Academy of Sciences.503(1): 17–54.Bibcode:1987NYASA.503...17C.doi:10.1111/j.1749-6632.1987.tb40596.x.PMID3113314.S2CID38405158.[permanent dead link]
  84. ^Madigan, Michael T. (2019).Brock biology of microorganisms(Fifteenth, Global ed.). NY, NY. pp. 70–71.ISBN9781292235103.{{cite book}}:CS1 maint: location missing publisher (link)
  85. ^abGhosh, Abhrajyoti; Albers, Sonja-Verena (1 February 2011). "Assembly and function of the archaeal flagellum".Biochemical Society Transactions.39(1): 64–69.doi:10.1042/BST0390064.PMID21265748.
  86. ^Thomas, Nikhil A.; Bardy, Sonia L.; Jarrell, Ken F. (April 2001). "The archaeal flagellum: a different kind of prokaryotic motility structure".FEMS Microbiology Reviews.25(2): 147–174.doi:10.1111/j.1574-6976.2001.tb00575.x.PMID11250034.S2CID34411164.
  87. ^Chimileski, Scott; Papke, R. Thane (2015)."Getting a hold on archaeal type IV pili: an expanding repertoire of cellular appendages implicates complex regulation and diverse functions".Frontiers in Microbiology.6:362.doi:10.3389/fmicb.2015.00362.ISSN1664-302X.PMC4419858.PMID25999922.
  88. ^de Sousa Machado, J. Nuno; Vollmar, Leonie; Schimpf, Julia; Chaudhury, Paushali; Kumariya, Rashmi; van der Does, Chris; Hugel, Thorsten; Albers, Sonja-Verena (2021)."Autophosphorylation of the KaiC-like protein ArlH inhibits oligomerization and interaction with ArlI, the motor ATPase of the archaellum".Molecular Microbiology.116(3): 943–956.doi:10.1111/mmi.14781.ISSN0950-382X.PMID34219289.
  89. ^Nuno de Sousa Machado, João; Albers, Sonja-Verena; Daum, Bertram (2022)."Towards Elucidating the Rotary Mechanism of the Archaellum Machinery".Frontiers in Microbiology.13.doi:10.3389/fmicb.2022.848597.ISSN1664-302X.PMC8978795.PMID35387068.
  90. ^Jarrell, Ken F; Albers, Sonja-Verena; Machado, J Nuno de Sousa (2021)."A comprehensive history of motility and Archaellation in Archaea".FEMS Microbes.2:xtab002.doi:10.1093/femsmc/xtab002.ISSN2633-6685.PMC10117864.PMID37334237.
  91. ^abLongcore, Joyce E.; Pessier, Allan P.; Nichols, Donald K. (March 1999). "Batrachochytrium Dendrobatidisgen. etsp. nov.,a Chytrid Pathogenic to Amphibians ".Mycologia.91(2): 219–227.doi:10.2307/3761366.JSTOR3761366.

Further reading

[edit]
[edit]

Public DomainThis article incorporates text from a publication now in thepublic domain:Chambers, Ephraim,ed. (1728).Cyclopædia, or an Universal Dictionary of Arts and Sciences(1st ed.). James and John Knapton, et al.{{cite encyclopedia}}:Missing or empty|title=(help)