what is flagella

What is flagella ?

2013-01-13T02:30:00.001-08:00

What is Flagella ?

Germination of Flagella:

what is flagella ?Flagella Is A modern science that draws attention of biologists because the three known varieties of flagella which are:

1. Eukaryotic Flagella

2. Bacterial Flagella

3. Archaeal Flagella

Each one of the above three Kinds of flagella represents a cellular structure that requires the interaction of many different and various systems.

We will give a brief description of the three varieties of flagella then we will give a detailed discussion about them on our website What is flagella (whatisflagella.us).

Euglena

2012-12-17T03:16:00.000-08:00

What is Euglena?

Euglena is unicellular organisms grouped into the Kingdom Protista, and the Phylum Euglenophyta. All euglena have chloroplasts and can make their own food by photosynthesis. They are not absolutely autotrophic though, euglena can also process food from their surroundings; euglena generally lives in silent ponds or puddles.

Movement of Euglena:

Euglena move by a flagellum (flagella), which is a burrs from some cells that assist in cellular locomotion. The flagellum is found on the anterior end, and twirls in such a way as to pull the cell via the water. It is connected at an inside pocket known as the reservoir.

Characteristics and Arrangements of Euglena:

The Euglena is special in that it is both heterotrophic (must consume food) and autotrophic (can make its own food). Chloroplasts within the euglena trap sunlight that is used for photosynthesis, and can be observed as various rods like structures all over the cell. Euglena also have an eyespot at the anterior end that detects light, it can be seen close to the reservoir. This assists the euglena find bright locations to collect sunlight to make their food. Euglena can also get nutrients (vitamins and minerals) by absorbing them throughout their cell membrane, therefore they grow to be heterotrophic when light is not available, and they cannot photosynthesize.

When feeding as a heterotroph, the Euglena surrounds a particle of food and consumes it by phagocytosis. When there is sufficient sunlight for it to feed by phototrophy, it uses chloroplasts containing the pigments Chlorophylla and Chlorophyll b to produce sugars by photosynthesis. Euglena's chloroplasts are surrounded by three membranes, while those of plants and the green algae (among which earlier taxonomists often placed Euglena) have only two membranes. This fact has been taken as morphological evidence that Euglena's chloroplasts evolved from a eukaryotic green algae. Thus, the intriguing similarities between Euglena and the plants would have arisen not because of kinship but because of a secondary endosymbiosis. Molecular phylogenetic analysis has lent support to this hypothesis, and it is now generally accepted.

The euglena has a stiff pellicle outside the cell membrane that assists it retain its form, though the pellicle is relatively flexible and some euglena can be noticed scrunching up and moving in an inchworm type fashion.

In the center of the cell is the nucleus, which includes the cell's DNA and controls the cell's actions. The nucleolus can be observed within the nucleus.

The interior of the cell includes a jelly-like liquid substance called cytoplasm. Toward the posterior of the cell is a star-like structure: the contractile vacuole. This organelle assists the cell eliminate extra water, and without it the euglena could take in some much water due to osmosis that the cell would explode

2012-12-12T11:51:00.000-08:00

This Video Shows How Flagella and Cilia Moves
what is flagella

Cilia And Flagella

2012-12-12T02:48:00.000-08:00

What Are Cilia and Flagella

Cilia and flagella are burrs from some cells that assist in cellular locomotion. They are formed from specialized groupings of microtubules known as basal bodies.

If the protrusions are small and several they are called cilia. If they are longer and less numerous (usually only one or two) they are called flagella.

Some Identifying Features:

Typically cilia and flagella have a core consisting of microtubules linked to the plasma membrane arranged in what is known as a 9 + 2 pattern.

The pattern is so named since a ring of nine microtubule "doubles" has in its center two singular microtubules.

This organization allows the slipping of the microtubule doubles against one another to "bend" the cilia or flagella. This type of organization is found in most eukaryotic cilia and flagella

A flagellum is a whip-like tail; usually cells only have one, occasionally two, and help the cell to move. Cilia and flagellum are only found on animal cells and not all animal cells have them.

Cilia are minor whips like structures that cover a cell and help it to move, move liquid that is all over it or to clean something.

Where can cilia and flagella are found

Both cilia and flagella are found in numerous types of cells. For example, the sperm of many animals, algae, and even ferns have flagella.

Cilia can be found in areas such as the respiratory and female reproductive tracts.

Movements of Flagella and Cilia

Strictly speaking are the cilia and flagellar movements of eucaryotes intracellular movements; for although a flagellum (or a cilium) appears to be an appendage of the cell, is it encircled by the plasma membrane. All dynein molecules along the whole length of the microtubule have continuously to be supplied with adequate volumes of ATP. Both ion milieu and pH of their surrounding has to be right.

P. SATIR (1968, 1976 at that time at the University of California, Berkeley) defined the process of movement as a sliding filament mechanism where the peripheral tubuline doublets slide past each other. In the course of this contacts the dynein that is always anchored to the A tubule the B tubule of the neighboring doublet with its tips.

This mechanism describes the forward and backward swings of the cilium but not the numerous modifications of cilia movements found mainly with protozoa. There exist pulling and pushing flagella, as well as tinsel-type flagella. There exist flagella that move around an imaginary axis and flexible flagella where the movement spreads wave-like along the axis. Many motile cells can switch into forward or backward gear or can bring out additional or a less strong improvements of the course.

Cilia differ from flagella only in their number per cell. They are usually quite short and cover often the whole surface of a cell. Cilia are rare in plants, an often cited example are the zoospores of Vaucheria sessilis.

With algae (except red algae) are flagellated stages common. They are often found with the spermatozoids (male germ cells) of mosses and ferns. Early during the evolution of seed plants were flagellated stages more and more driven out. Among the few still existing exceptions are the spermatozoids of Gingko biloba and the cycads.

Movements are often controlled by extern indicators. Many protists are attracted by specific resources of pleasure called taxis: light (phototactic behaviour) or certain chemicals (chemotactic behaviour). Normally comes after the movement a concentration or intensity gradient. If a threshold of sensation is passed, begins a backward response. During the last generations was signal recognition a much-studied topic. We know, for example, that the carotenoids within the stigma of some algae (Euglena, for example) are very sensitive to blue light. The chloroplast movements of the alga Mougeotia are managed by thephytochrome system and germ cells (of algae) respond to varieties certain sexual attractants. But how the perceived signal is transformed and how signals of the same or the opposite kind are co-ordinated in a guided motion is not even basically understood.

The basis of many flagella is outfitted with a complexly structured basal body. M. MELKONIAN (Botanisches Institut der Universität Köln) examined the basal bodies of a number of algae and found group-specific patterns. He ranked these structures and their differences as features that help to understand the family relationships of the single groups of algae significantly.

Types of cilia and flagella

There two types of cilia: motile and non-motile or primary cilia:

A. Non-motileor primary cilia are found in nearly every cell in all mammals and as the name suggests these do not beat. They can be found in human sensory organs such as the eye and the nose.

B. Motilecilia are found on the surface of cells and they beat in a rhythmic manner. They can be found in the lining of the trachea (windpipe), where they sweep mucus and dirt out of the lungs. In female mammals, the beating of cilia in the fallopian tubes moves the ovum from the ovary to the uterus.

There are three types of flagella: bacterial, archaeal and eukaryotic:

A. Bacterialflagella are helical filaments that rotate like screws. They are found in E. coli, Salmonella typhimurium. There may be one, two or many such flagella per cell. These flagella provide motility to bacteria.

B. Archaealflagella are similar to bacterial flagella but they have a unique structure which lacks a central channel.

C. Eukaryoticflagella are complex cellular projections that lash back and forth. (e.g., the sperm cell, which uses its flagellum to move itself through the female reproductive tract.

Diseases:

Lack of proper functioning of cilia and flagella can cause several problems in human beings, For example:

If the cilia in the fallopian tubes are not functioning properly then the fertilized ovum will not reach the uterus and thus result in ectopic pregnancy.

A defect of the main cilium in the renal tube cells can lead to polycystic kidney disease.

Flagellum dysfunction can also be responsible for male infertility because the sperm is not motile and cannot swim to the ovum.

What Is Flagella

2012-12-10T05:27:00.002-08:00

Germination of Flagella:

What is Flagella ?

Flagella Is A modern science that draws attention of biologists because the three known varieties of flagella which are:

1. Eukaryotic Flagella

2. Bacterial Flagella

3. Archaeal Flagella

Each one of the above three Kinds of flagella represents a cellular structure that requires the interaction of many different and various systems.

We will give a brief description of the three varieties of flagella then we will give a detailed discussion about them on our website What is flagella (whatisflagella.us).

What is flagella ( Definition)

Flagella are more than one flagellum. A flagellum is a cell with a tail like structure attached to it. The tail like structure moves kind of like a whip, but in circular motions.

in other words : flagella are burrs from some cells that assist in cellular locomotion

Overview about the Three Varieties of Flagella

2012-12-10T05:26:00.000-08:00

Overview about the Three Varieties of Flagella

Below Is An Overview Of The Three Varieties Of Flagella Which Are:

A- Eukaryoticflagella

B- Bacterial flagella

C-Archaeal flagella

A-Eukaryotic flagella:

There are two competitive categories of designs for the transformative source of the eukaryotic flagella .

Endogenous, autogenous and quick filiation's models:

These designs claim that cilia developed from pre-existing components of the eukaryotic cytoskeleton "which has tubulin and dynein, also used for other functions" as an expansion of the mitotic spindle equipment. The relationship can still be seen, first in the various early branching single-celled eukaryotes that have a microtubule basal body system, where microtubules on one end type a spindle-like cache around the nucleus, while microtubules on the other end element away from the mobile and kind the Eukaryotic. A further relationship is that the centriole, engaged in the development of the mitotic spindle in several "but not all" eukaryotes, is homologous to the Eukaryotic, and in many situations is the basal body system from which the Eukaryotic develops.

An evident advanced level between spindle and Eukaryotic would be non-swimming appendages created of microtubules with a selectable operate like improving surface place, supporting the protozoan to stay revoked in water, improving the possibilities of thumping into parasites to eat, or offering as a stalk linking the mobile to a powerful substrate.

Regarding the source of the person necessary protein elements, an exciting document on the progress of dyneins[1][2] reveals that the more complicated necessary protein category of ciliary dynein has an obvious ancestor in a easier cytoplasmic dynein (which itself has progressed from the AAA necessary protein close relatives that happens commonly in all archea, parasites and eukaryotes). Long-standing doubts that tubulin was homologous to FtsZ (based on very poor series likeness and some behavior similarities) were verified in 1998 by the separate quality of the 3-dimensional components of the two necessary proteins.

Symbiotic/endosymbiotic/exogenous models

These designs claim that the Eukaryotic progressed from a union spirochete that connected to a basic eukaryote or archaebacterium (archaea). The contemporary edition of the speculation was first recommended by Ruby Margulis.[3] The speculation, though very well promoted, was never commonly approved by the professionals, contrary to Margulis' justifications for the union source of mitochondria and chloroplasts. Margulis did highly enhance and post editions of this speculation until the end of her lifestyle.

The main factor in support of the union speculation is that there are eukaryotes that use union spirochetes as their mobility organelles (some parabasalids within pest courage, such as Mixotricha and Trichonympha). While this is an example of co-option and the versatility of scientific techniques, none of the recommended homologies that have been revealed between cilia and spirochetes have was status up to further analysis. The homology of tubulin to the microbe duplication and cytoskeletal necessary protein FtsZ is a significant discussion against Margulis, as FtsZ appear to be discovered natively in archaea, offering an endogenous ancestor to tubulin (as compared to Margulis' speculation, that an archaea obtained tubulin from a union spirochete(.

B-Bacterial flagella:

A strategy to the transformative source of the microbe flagella is recommended by the point that a part of flagellar elements is just like the Kind III secretory and transportation program.

All currently known nonflagellar Kind III transportation techniques provide the operate of treating poisons into eukaryotic tissues. It is hypothesised that the flagella progressed from the kind of three secretory program. For example, the bubonic affect bacteria Yersinia pestis has an organelle set up very just like a complicated flagella, except that is losing only a few flagellar systems and features, such as a hook to provide poisons into other tissues. It is also a probability that the flagella could have progressed from a currently hidden program with identical flagellar attributes or a currently vanished organelle/organism.[citation needed] As such, the kind of three secretory program facilitates the speculation that the flagella progressed from a easier microbe release program.

C-Archaeal flagella:

The lately elucidated archaeal flagella is similar, not homologous, to the microbe one. Moreover to no series likeness being recognized between the genetics of the two techniques, the archaeal flagellaseems to develop at the platform rather than the tip, and is about 15 nanometers (nm) across rather than 20. Sequence evaluation indicates that the archaeal flagella is homologous to Kind IV pili.[5] (pili are filamentous components outside the cell). Remarkably, some Kind IV pili can withdraw. Pilus retraction provides the power for a different way of microbe mobility known as "twitching" or "social gliding" which allows microbe tissues to spider along a surface place. Thus Kind IV pili can, in different parasites, enhance either diving or creeping. Kind IV pili are constructed through the Kind II transportation program. So far, no varieties of parasites are known to use its Kind IV pili for both diving and creeping.

Testable describes are available for the source of each of the three mobility techniques, and methods for further analysis are clear; for prokaryotes, these methods consist of the analysis of release techniques in free-living, nonvirulent prokaryotes. In eukaryotes, the systems of both mitosis and Eukaryotic development, such as the key part of the centriole, need to be much better recognized. A specific study of the various nonmotile appendages discovered in eukaryotes is also necessary.

Eukaryotic Flagella

2012-12-10T05:24:00.000-08:00

The First one of the three varieties of flagella is eukaryotic, below is a more detailed discussion about it, I hope that you will find it useful and helpful.

Eukaryotic Flagella:

A eukaryotic flagellum is a pack of nine merged pairs of microtubule doublets encirclement two core single microtubules. The so-called "9+2" structure is feature of the central of the eukaryoticflagellum known as an axoneme. At the starting of a eukaryotic flagellum is a basic body, "blepharoplast" or kinetosome, which is the microtubule organizing center (MTOC) for flagellar microtubules and is about 500 nanometers long. Basal bodies are structurally identical to centrioles. The flagellum is encased within the cell's plasma membrane, so that the inner of the flagellumis attainable to the cell's cytoplasm

Mechanism:

Each of the outer 9 doublet microtubules increases a couple of dynein arms (an "interior" and an "exterior" arm) to the adjacent microtubule; these dynein arms are responsible for flagellar defeating, as the force generated by the arms reasons the microtubule doublets to skid with each other and the flagellum as a whole to fold. These dynein arms produce force through ATP hydrolysis. The flagellar axoneme also contains radial spokes, polypeptide complexes extending from each of the outer 9 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.

Flagella versus cilia:

Alternative of beating structure of flagellumand cilia

The regular beat patterns of eukaryotic cilia and flagella produce movement on a cellular level. Examples range from the propulsion of single cells such as the swimming of spermatozoa to the transfer of liquid along a stationary layer of cells such as in the respiratory tract. Though eukaryotic flagella and motile cilia are ultrastructurally identical, the beating pattern of the two organelles can be distinct. In the case of flagella the motion is often planar and wave-like, whereas the motile cilia often perform a more complex 3D activity with a power and recovery stroke.[citation needed]

Intraflagellar transport:

Intraflagellar transport (IFT), the method by which axonemal subunits, transmembrane receptors, and other proteins are relocated up and down the length of the flagellum, is essential for appropriate functioning of the flagellum, in both motility and signal transduction

Bacterial Flagella

2012-12-10T05:22:00.002-08:00

Bacterial Flagella

The bacterial flagellum is made up of the protein flagellin. Its shape is a 20 nanometer-thick blank tube. It is helical and has a acute bend just outside the outer membrane; this "hook" allows the center of the helix to point directly away from the cell. A shaft runs between the hook and the basal body, passing through protein rings in the cell's membrane that act as bearings. Gram-positive organisms have 2 of these basal body rings, one in the peptidoglycan layer and one in the plasma membrane. Gram-negative organisms have 4 such rings: the L ringassociates with the lipopolysaccharides, the P ring associates with peptidoglycan layer, and the M ring is embedded in the plasma membrane, and the S ring is directly attached to the plasma membrane. The filament ends with a capping protein.

The bacterial flagellum is driven by a rotary engine (the Most complex) made up of protein, located at the flagellum's anchor point on the inner cell membrane. The engine is powered by proton motive force, i.e., by the flow of protons (hydrogen ions) across the bacterial cell membrane due to a concentration gradient set up by the cell's metabolism (in Vibrio species there are two kinds of flagella, lateral and polar, and some are driven by a sodiumion pump rather than a proton pump) The rotor transports protons across the membrane, and is turned in the process. The rotor alone can operate at 6,000 to 17,000 rpm, but with the flagellar filament attached usually only reaches 200 to 1000 rpm. The direction of rotation can be switched almost instantaneously, caused by a slight change in the position of a protein, FliG, in the rotor.

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

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 / second. Although at such a speed it would take a bacterium about 245 days to cover a kilometer, and 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 sec.

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. In vitro, flagellar filaments assemble spontaneously in a solution containing purified flagellin as the sole protein.

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 negative Escherichia coli, Salmonella typhimurium, Caulobacter crescentus, and Vibrio alginolyticus, the filament is made up of eleven protofilaments approximately parallel to the filament axis. Each protofilament is a series of tandem protein chains. However in Campylobacter jejuni, there are seven protofilaments.

The basal body has several traits in common with some types of secretory pores, such as the hollow rod-like "plug" in their centers extending out through the plasma membrane. Given the structural similarities between bacterial flagella and bacterial secretory systems, it is thought that bacterial flagella may have evolved from the type three secretion system; however, it is not known for certain whether these pores are derived from the bacterial flagella or the bacterial secretory system.

Through use of their flagella, E. coli are able to move rapidly towards attractants and away from repellents. They do this by means of abiased random walk, with 'runs' and 'tumbles' brought about by rotating the flagellum counter-clockwise and clockwise respectively.

Flagella arrangement schemes

Examples of bacterial flagella arrangement schemes:

A-Monotrichous

B-Lophotrichous

C-Amphitrichous

D-Peritrichous

Different species of bacteria have different numbers and arrangements of flagella. Monotrichous bacteria have a single flagellum (e.g.,Vibrio cholerae). Lophotrichous bacteria have multiple flagellalocated at the same spot on the bacteria's surfaces 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, the so-called polar membrane.[citation needed] Amphitrichous bacteria have a single flagellum on each of two opposite ends (only one flagellum operates at a time, allowing the bacteria to reverse course rapidly by switching which flagellum is active). Peritrichous bacteria have flagella projecting in all directions (e.g., E. coli).

I Selenomonas, the individual flagella are organized outside the cell body, helically twining about each other to form a thick structure called a "fascicle". Other bacteria, such as Spirochetes, have a specialized type of flagellum called an "axial filament" that is located in the periplasmic space, the rotation of which causes the entire bacterium to move forward in corkscrew-like motion.

Counterclockwise rotation of monotrichous polar flagella pushes the cell forward with the flagella trailing behind, much like a corkscrew moving inside cork. Indeed water in the microscopic scale is highly viscous, very different from our daily experience of water. The flagella are left-handed helices, and bundle and rotate together only when rotating counterclockwise. When some of the rotors reverse direction, the flagella unwind and the cell starts "tumbling". It has also been suggested that even if all flagella would rotate clockwise, they will not form a bundle, due to geometrical as well as hydrodynamic reasons Such "tumbling" may happen occasionally, leading to the cell seemingly thrashing about in place, resulting in the reorientation of the cell. The clockwise rotation of a flagellum is suppressed by chemical compounds favorable to the cell (e.g. food), but the motor is highly adaptive to this. Therefore, when moving in a favorable direction, the concentration of the chemical attractant increases and "tumbles" are continually suppressed; however, 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.

In some Vibrio spp. (particularly Vibrio parahemolyticus) and related proteobacteria such as Aeromonas, 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.

Archaeal Flagella

2012-12-10T05:19:00.002-08:00

Archaeal Flagella

The archaeal flagellum is a complicated cellular composition made up of several subunits and anchored to the membrane and it is a unique motility apparatus different in structure and most likely in assembly from the bacterial flagellum.

Gene families consist of multiple flagellin genes co-transcribed with a number of conserved, archaeal-specific accessory genes have been specified in many archaea. However, no homologues of any bacterial genes involved in flagella structure have yet been recognized in any archaeon, such as those archaea in which the complete genome series has been published. Archaeal flagellins possess a highly conserved hydrophobic N-terminal sequence that is comparable to that of type IV pilins and definitely as opposed to that of bacterial flagellins. Also unlike bacterial flagellins but very similar to type IV pilins, archaeal flagellins are initially synthesized with a small leader peptide that is cleaved by a membrane-located peptidase. With modern developments in genetic transfer systems in archaea, knockouts have been described in various genes included in flagellation in distinct archaea. In addition, techniques to isolate flagella with attached hook and anchoring structures have been developed. Analysis of these preparations is under way to identify minor structural elements of archaeal flagella. This and the ongoing seclusion and depiction of flagella mutants should lead to important developments in our knowledge of the composition and assembly of archaeal flagella.

The striking conservation of the genomic context of the genes coding for these subunits indicates a likely highly coordinated expression and assembly mechanisms. Coupled to the high sequence conservation of the different subunits across archaeal species inhabiting very different habitats, this underlines the importance for structural maintenance of the archaeal flagellum. However, we highlighted a significant dimorphism of the genetic context organization, with two types of gene clusters harboring variations in both gene content and gene order. Actually, most Euryarchaea show the fla1 cluster, whereas all the Crenarchaea and some Euryarchaea have the fla2 cluster (e.g. Methanomicrobia and A. fulgidus). The variation between the two clusters is highly supported by phylogenetic research, and shows that Methanomicrobia and A. fulgidus flagellum elements encoded by fla2 gene clusters are much more directly related to their crenarchaeal homologues than to the homologues encoded by the fla1 gene cluster of their close relatives (i.e. M. burtonii, Thermoplasmatales and Halobacteriales. Two various evolutionary scenarios can be proposed to describe our outcomes. In the first case, the last ancestor of Archaea was flagellated and had the two kinds of clusters (i.e. bothfla1 and fla2, blue and red clusters, accordingly, resulting from the duplication of an ancestral cluster (purple cluster, and these were secondarily and diversely missing throughout archaeal lineages evolution (seven losses of the fla1 cluster and nine losses of the fla2 cluster). Importantly, some of these losses would have also occurred recently in the Euryarchaea (for example the loss of the fla1 cluster in the Methanosarcinale lineage would have happened following the divergence of M. burtonii, that would have kept the two types of clusters). Last but not least, a replication event of the whole fla2 cluster occurred in an ancestor of Methanosarcina (red circle) leading to the fla2B cluster (orange cluster, )This first situation consists of 16 losses, and implies that the ancestor of Archaea and the ancestor of each euryarchaeal class had two types of flagella. Moreover, it does not describe the position of A. fulgidus sequences inside the Methanomicrobia group and not as sister of this group, as generally specified by molecular phylogeny of numerous markers. A second situation consists of less losses (three losses of the fla2 cluster and seven losses of the fla1 cluster) Here, the progenitor of Archaea was also flagellated, but had only a single type of fla cluster (either fla1, fla2, or else, purple cluster). Following the divergence of Crenarchaea and Euryarchaea (black circle) evolution led to the fla1 and fla2 clusters. A single HGT of the fla2 cluster would have then happened from some ancestors of Sulfolobales and Desulfurococcales to an progenitor of Methanomicrobia, and was followed by a HGT from some ancestors of Methanosarcinales to A. fulgidus. Methanosarcina, M. hungatei and A. fulgidus would thus have lost their original fla1 gene cluster before or after their replacement by a fla2 gene cluster of crenarchaeal radix. We support a HGT from Crenarchaea to Methanomicrobia rather than the opposite, given that in this case we would assume to find the M. burtonii fla1 genes more closely related to their paralogues belonging to the fla2 cluster than to their fla1 orthologues from Halobacteriales.

Both circumstances imply that the archaeal flagellum would have seemed in advance of the last archaeal ancestor

Aside these two likely situations of HGT of the whole fla2 gene cluster, we found no obvious facts for recent transfers of the genes coding for flagellum elements among archaeal species. In fact, the poor resolution of inter-phyla relationships in some trees is more likely due to absence of phylogenetic signal rather than horizontal gene transfer. One justification for the rarity of HGT is that it is probable the result of the high level of integration of flagellum elements within the macromolecular structure. Importantly, this contradicts the generally assumed notion that HGT of "informational" genes (i.e. those coding for proteins involved in the expression and the transmission of genetic information) are less consistent than those involving the remaining ones ("operational") genes. Nevertheless, the acquisition of a whole flagellum component coding gene cluster from distant donors seems possible. Interestingly, even if two clusters coexist within a genome (i.e. in M. burtonii) neither gene recombination is observed between homologous genes belonging to the two clusters, nor losses, suggesting that the components of a cluster may interact preferentially due to coevolution, although they form similar cellular structures. The presence in M. burtonii of two types of fla clusters (possibly one native and one acquired by HGT from crenarchaeota) represents an interesting experimental model to study. It would be in fact particular interesting to know the distinction between the components encoded by the two flaclusters in terms of expression and assembly, and how two different flagellum systems coexist in this archaeon.

Last but not least, it has been indicated that archaea are improved Actinobacteria and that archaeal flagella are derived from bacterial flagella following an adaptation to acidic environments by the recruitment of an already acid-stable glycoprotein from the pilus machinery that would have replaced the original flagellin while leaving intact the basal rotary motor. We find this hypothesis unlikely for the fact that archaeal flagella do not resemble to bacterial flagella in key structure, system, and components, and not only regarding flagellin. Indeed, no even far away homologues to any component, including the basal rotary motor, of bacterial flagella can be recovered in archaeal genomes, including the related type III secretion system components. Moreover, flagella of acidophilic bacteria (such as Thiobacillus) show a typical bacterial structure (e.g. a diameter of approximately 20 nm), so they adapted to acidic conditions without radically modifying their motility structures and components.

The lack of congruence between the description of archaeal species as motile or non-motile and the taxonomic distribution of homologues of flagellum component coding genes is particularly striking and underlines the need to explore more in depth the motility systems in Archaea. The presence of two gene clusters in non motile Methanosarcinales is particularly puzzling. Either these species can be flagellated under particular conditions that have not yet been tested, or the flagellum component homologues are involved in other functions than motility (for example, they could be required for cell-cell adhesion to form cell aggregates, a peculiarity of this archaeal family). It will be extremely interesting to study the expression and localization of the flagellum components in Methanosarcinales, in the light of the fact that the flagellum genes of Methanosarcinales may have been recruited from the distantly related Crenarchaeota, since this event may have been an important step in the evolution of this archaeal lineage. Moreover, virtually nothing is known about other types of motility than swimming in archaea, while in bacteria these are starting being investigated. The fact that no homologues of flagellumcomponents are encoded in the genomes of at least two archaeal species that are described as motile (M. kandleri and P. aerophilum) is also puzzling. Although it is possible that the strains used for genome sequencing have lost the flagellum operon following lab cultivation it would surely be interesting to test motility in these archaeal species. Alternatively, this observation could also suggest that other types of motility may occur in archaea and are made possible by still unknown molecular structures. It would also be very useful to investigate the relationship between the flagellum and the secretion systems in Archaea. Indeed, archaeal genomes harbor only a few homologues of bacterial TypeII/IV secretion systems, and it is not known whether they form pili, despite rare observations and evidence for conjugation.

To summarize, two drastically various alternatives for mobility were used at the Variation of the two prokaryotic areas, and much still keep to be exposed on archaeal motility systems.

Bottom line is: the archaeal flagellum is a special mobility organelle. While ostensibly comparable to the bacterial flagellum, many similarities have been reported between the archaeal flagellum and the bacterial type IV pilus system. These include the multiflagellin nature of the flagellar filament, N-terminal sequence similarities between archaeal flagellins and bacterial type IV pilins, as well as the existence of homologous proteins in the two systems. Latest developments in archaeal flagella analysis add to the growing list of similarities. First, the preflagellin peptidase that is responsible for processing the N-terminal signal peptide in preflagellins has been discovered. The preflagellin peptidase is a membrane-bound enzyme topologically similar to its counterpart in the type IV pilus system (prepilin peptidase); the two enzymes are demonstrated to utilize the same catalytic mechanism. Second, it has been encouraged that the archaeal flagellum and the bacterial type IV pilus share a comparable mode of assembly. While bacterial flagellins and type IV pilins can be modified with O-linked glycans, N-linked glycans have recently been reported on archaeal flagellins. This mode of glycosylation, as well as the declaration that the archaeal flagellum does not have a central channel, are both consistent with the proposed assembly model. On the other hand, the inability to discover other genes included in archaeal flagellation by homology searches most likely implies a novel aspect of the archaeal flagellar system. These interesting features remain to be deciphered through continued research. Such knowledge would be invaluable to motility and protein export studies in the Archaea.

Cilia and Flagella

2012-12-10T05:17:00.000-08:00

This video describes the major differences between flagella and cilia and how do they move and operate.

Bacterial Flagellum

2012-12-10T04:18:00.000-08:00

This video describes how bacteria use flagella to propel themselves through their environment

Flagella movement

2012-12-10T04:09:00.000-08:00

This video shows flagella movement

Prokaryotic and Eukaryotic Cells

2012-12-10T04:01:00.000-08:00

This video shows the composition of Prokaryotic and Eukaryotic Cells

Growth of Flagella

2012-12-10T03:54:00.000-08:00

Introductory video about flagella and how it grow

Flagella and Cilia Movement

2012-12-10T03:39:00.000-08:00

Flagella Movement:

Most flagellate protozoans have either one or two flagella extending from the front end of the body. Some protozoans, however, have various flagella that may be sprinkled over the whole body; in such situations, the flagella generally are merged into noticeably distinct clusters. Flagellar mobility, or movement, happens as either planar waves, oarlike whipping, or three-dimensional waves. All three of these forms of flagellar movement consist of shrinkage waves that override either from the bottom to the tip of the flagellum or in the invert way to generate ahead or in the opposite direction movement. The planar waves, which happen along a individual plane and are very similar to a sinusoid (S-shaped) wave form, seem to be asymmetrical; there is a gradual increase in amplitude (peak of the wave) as the wave moves to the tip of the flagellum. In planar movement the movement of the flagella is equal to that of the body of an eel as it swims. Even though symmetrical planar waves have been noticed, they obviously are abnormal, because the movement they produce is erratic. Planar waves cause the protozoan to rotate on its longitudinal axis, the path of movement tends to be helical (a spiral), and the direction of movement is opposite the propagation direction of the wave.

In oarlike flagellar movements, which are also planar, the waves seem to be highly asymmetrical, of greater side to side swing, and the protozoan generally revolves and moves with the flagellum at the forward end. In the three-dimensional wave form of flagellar movement, the motion of the flagella is very similar to that of an airplane propeller; i.e., the flagella lash from side to side. The flagellum moves in a conical configuration, the apex (tip) of which centres on the point at which the flagellumis attached to the body. Simultaneous with the conical rotation, asymmetrical sinusoidal waves pass from the starting to the end of the flagellum. As a effect of the flagellar rotation and its changing direction of contact, water is forced backward over the protozoan, which also seems to rotate, and the organism moves forward in the direction of the flagellum.

Cilia Movement:

Cilia operate like flexible oars; they have a one-sided beat lying in a single plane. As a cilium moves backward, it is relatively rigid; upon recovery, however, the cilium becomes flexible, and its tip seems to be drawn forward along the body. Because the cilia possibly completely cover, as in ciliate protozoans, or are set up in groups or clumps, the movement of each cilium must be closely matched up with the movements of all other cilia. This coordination is accomplished by metachronal rhythm, in which a wave of simultaneously beating groups of cilia moves from the anterior to the posterior end of the organism. In addition to preventing interference between adjacent cilia, the metachronal wave also makes ongoing forward movement because there are always groups of cilia beating backward. Furthermore, because the plane of the ciliary beat is

diagonal to the longitudinal axis of the body, ciliate organisms rotate during movement.