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Bacterial bronchitis cure,how to get rid of a sore throat from a cold 2014,how to get rid of sore arms after working out,how to get rid of nail fungus the natural way cafe - For Begninners

Bacteria (singular bacterium) are minute organisms that often consist of single cells, like the rod-shaped cell shown above which is about one thousandth of a millimetre (mm) in diameter (that is one micrometre or about a tenth the diameter of one of your cells or about one thousandth the volume of a human cell), but may exist as filaments (chains of cells) or cubes of cells or as large 'slime cities' or biofilms that may be easily visible to the naked eye. Above: a simplified version of the bacterial cell structure diagram, showing the structures most frequently encountered in elementary biology courses. In these cross-sections, the double membrane, separated by periplasm, characteristic of Gram negative bacteria can be seen. The diagram above shows a very high magnification image of the cell envelope of Bacteroides fragilis. Many bacteria are now known to alternate between single-celled swarmers that disperse to find new habitats, and colonies or 'cities' held together by slime. This resembles the bacteria that live in thick mud, and those that cause diseases in humans such as Lyme's disease and syphilis. Shown in purple is the tough capsule or cell wall of the bacterium (this is a type of bacterium known as Gram positive, but there are other structural types with different wall arrangements). These are bacteria that have been cut into sections some 70 millionths of a millimetre thick and viewed under a powerful electron microscope.
Notice that the peripheral cytoplasm is granular (due mostly to ribosomes) and in the central nucleoplasm you can see strands of DNA (with attached proteins).
The bacillus cell-body is essentially a cylinder with hemispherical end-caps, as modeled here. The outer membrane is budding off vesicles (a characteristic of Bacteroides fragilis) and the peripheral cytoplasm is electron-dense (appears dark under the electron microscope) and is rich in ribosomes (dark granules) forming a riboplasm.
When moving forward, the flagella come together to form a propulsive flagella-bundle at the rear of the cell.
Bacteria rely on nutrients reaching the cell, crossing the cell envelope and then moving around within the cell where they are used. Comma-shaped bacteria are similar to the helical spirochaetes except that instead of spanning many turns of the helix they have less than a single turn along their length. As they move they rotate like a corkscrew, and this allows them to bore their way into thick mud, or into your tissues!
The bottom picture shows a close up view of one cell in the act of splitting into two new daughter cells. Notice that the surface of this bacterium type appears somewhat 'hairy', actually in life these 'hairs' absorb water and form a slimy outer layer. Inside the shell of periplasm is the nucleoid, which appears largely transparent (like white spaces, but of course there are no spaces here in life) with criss-crossing fibrils of DNA. Each membrane displays the trilaminar (three-layered) appearance characteristic of unit membrane composed of a double lipid bilayer (two leaflets), with an electro-lucent (pale layer) sandwiched between two electron-dark layers. Those that obtain nutrients from a surface may have adhesive structures, such as pili or slime capsules.Many of these cells are motile - they can swim by means of flagella (or move in other ways). These types can be quite long cells, up to about one fifth of a millimetre in length, but it is quite narrow.Bacteria are the simplest cellular lifeforms we know of. For example, tuberculosis, leprosy, many stomach and bowl disorders (food poisoning) and syphilis are human diseases caused by bacteria. Shown in light blue is the peripheral cytoplasm which is bounded by a cell membrane which you can just see underneath the capsule. The flagella of many bacteria have two wavelength modes, one usually around 1 micrometre wavelength, and the other double this at 2 micrometres - the flagella can switch between these two modes. Between these membranes is the periplasm, which contains a thin-layer of peptidoglycan, which some consider to be a gel - certainly it is hard to discern this layer, though looking at the images above there does seem to be a thin dark layer visible in the middle of the periplasm in some regions.
On this microscopic scale water behaves as a very viscous treacle-like substance, it has a low Reynold's number, Re (see biorheology), meaning that viscosity dominates over inertial forces. Some species of Vibrio may have mixed flagellation: lots of flagella around the surface of the cell (peritrichous flagellation) and a thicker flagellum at one cell pole.
However, although a bacterial cell is much simpler than an animal or plant cell, they are still extremely complex, especially on the nanoscale! The cytoplasm consists mostly of water and proteins (including ribosomes that manufacture other proteins). Can you identify the cell envelope (cell wall, which has 4 layers in this type of bacterium, which is called the Gram negative type), the ribosome-rich peripheral cytoplasm and the central DNA-rich nucleoplasm? The scale refers to the enlarged image and shows that the width of each bacterial cell is about one micrometre or one thousandth of a millimetre across. This blebbing is characteristic of Bacteroides fragilis and the vesicles may contain toxins which are delivered to host cells and so play a role in virulence (Bacteroides fragilis is a component of the normal gut-flora in humans, but it can also cause infection, such as intra-abdominal sepsis and bacteremia). The outer leaflet of the outer membrane is coated with carbohydrate chains (chains of sugar molecules) called the glycocalyx.
The most efficient shape for swimming at such low Re is to have a length about 3.7 times the width, so rods are more efficient swimmers than spheres.
Convection is the bulk movement of materials in a fluid, such as when hot air rises or when the wind blows or water currents flow (advection).
In liquid culture Vibrio has a single sheathed flagellum at one pole of the cell (a sheathed flagellum is a normal bacterial flagellum covered by the outer membrane, more commonly, bacterial flagella have no membranous sheath. The earliest recognisablefossils are of bacteria which completely dominated the Earth 3.5 billion years ago!
Bacteria represent the simplest living cells we know of, however, they are still extremely complex. This membrane is similar to the membrane that forms the 'skin' of your own cells, and is also made up of mostly fats and proteins.
Notice that even this high magnification does not reveal most of the details of the complex nano-scale machinery that exists within the cell.The NucleoidThe bacterial genome usually consists of a single circular chromosome of double-stranded DNA.
In Pseudomonas aeruginosa similar vesicles have been shown to be involved in signalling (they carry quinolone signalling molecules involved in quorum sensing). These bacteria rotate as they swim and so can drill their way through thick mud, or in the case of the bacterium that causes syphilis (a spirochaete) they can drill through the tissues of the body, including tough cartilage. However, when grown on solid agar it develops additional unsheathed flagella that give it the motive power to crawl over the agar in a phenomenon called swarming. Bacteria resembling photosynthetic cyanobacteria formed large layered structures, called stromatolites along the shores of the early seas. The detailed structure of the ribosome, for example, has been determined by using cryo-electron microscopy, in which the cells are rapidly frozen (such as with liquid nitrogen) rather than fixed with chemicals, which reduces damage to the cell structure. On a smaller scale molecules can also move by diffusion, which becomes too slow at large scales. Stromatolites still dominate in areas like the Dead Sea, but in the ancient Earth they were the dominant life-form!
Viruses are not capable of independent life, but are parasites that must invade their particular host cell type, take control of the cell, and then use the cell’s machinery to make more copies of themselves – viruses are pirates of the cell!
The red threads are the DNA, because the nucleoplasm contains the genes and forms the central computer of the bacterial cell. In Escherichia coli, the single circular DNA molecule is supercoiled - the DNA helix is itself twisted around to form a helix of helical DNA.
Very careful sectioning then allows computer software to reconstruct the 3D structure on a nanometre scale! Much longer rods may occur when adhesion is important - a long rod that is aligned parallel to the direction of fluid-flow has a large surface area with which to adhere to a surface whilst presenting a small area against the current. When grown in fast-moving currents (high shear forces) Escherichia coli elongates and may form chains of cells, a possible adaptation to enhancing adhesion. In many ways bacteria are still thedominant life-form on earth today – there are more bacterial cells in your body than animal cells! Note that the bacterial cell has fewer internal compartments than the animal cell.Now, what about the long black coils? Bacillus subtilis responds differently, the cells become smaller and so present a smaller area to the oncoming fluid. Heterotrophs can not fix carbon, as photosynthetic organisms can, but instead rely on pre-made organic carbon sources which they obtain from other organisms. These are the engines of the bacterium and are called flagella (singular flagellum) which means 'whip' in Latin, which is a bit of a misnomer for bacteria because these flagella do not lash about but rotate like corkscrews.
The length of individual supercoiled domains (the lengths follow an exponential distribution) averages 10 kb (kilobases) and their are about 500 such loops or domains per chromosome.
Bacilli dividing by binary fission, tend to adhere to one-another, which favours the formation of a pavement of cells which covers a surface in such a way as to leave few gaps - the cells are packed together efficiently.On the other hand, cocci seem to disperse more easily. Bacteria are essential to every ecosystem as they transform and recycle chemicals and elements, for example in the carbon, oxygen, nitrogen and sulphur-cycles. Some heterotrophs are parasitic but most simply absorb the dead and decaying remains of other organisms - they are saprotrophs.
These motors are very fast, but not as good as drilling into thick materials like what the spirochaete can do by turning its whole body into a corkscrew!If you look carefully at the roots where the flagella join the cell body, then you will see what look like little wheels, indeed that is exactly what they are, but instead of driving the cell along as do the wheels on a car drive the car along, they drive the flagella and cause them to rotate like corkscrews, propelling the cell along.


Each domain contains DNA that is negatively supercoiled, meaning that it us unwound or undertwisted slightly (positive supercoiling winds the helix in the same direction, overwinding it).
There is some evidence that coccoids are carried more easily through bedrock in underground aquifers, possibly because the rods were adhering to the rock particles more efficiently along the way.
Saprotrophs secrete enzymes to digest dead and decaying organic matter which they then absorb.
Supercoiled strands are easier to separate, as must occur during DNA replication and when the DNA is read by polymerase enzymes to manufacture RNA (see protein synthesis).
Brownian motion (the jostling of tiny particles due to colliding water molecules) is important in the dispersal of non-motile forms and is most efficient for spheres, less so for flat cells and least efficient for rods (though there are other factors involved). These structures are dynamic, constantly fusing and dividing and being moved around inside your cells, and they perform a vital function – they burn fuels like glucose to provide cells with usable chemical energy packaged in ATP molecules. Some are commensals, which means they feed on the waste of other organisms whilst living on or inside them but cause no harm to the host, for example, 55% of the solid part of human faeces is bacteria! It is possibly to demonstrate supercoiling with a piece of thread or an elastic band - wind it evenly to start with, like a DNA helix, then see what happens if overwind or underwind it slightly and hold the ends together in a circle. Thus, it may be favourable for non-motile forms to be coccoid or to produce coccoid cells for dispersal (rather like spores).Finally, it should be realised that bacterial cell shape is not rigid, some bacteria can be rod-shaped or spherical (or some other shape) depending on the conditions.
In large bacteria, inclusions (storage reserves that form granules in the cytoplasm) reduce the volume of active cytoplasm.
These mitochondria are the descendents of bacteria that entered the ancestral cell billions of years ago!
Most are, however, tiny by cell standards, because they rely on diffusion they can maximise transport of materials across their cells by being small or at least narrow. Only the fastest and largest swimming bacteria known, Thiovulum majus, can increase convective nutrient supply by its own motility, that is it can generate water currents by moving about and these bacteria actively ventilate their population. You are a composite organism since you are part bacteria!Bacteria are generally considered to be single-celled organisms as those most closely studied historically were isolated swarmer cells, like the one above.
Click here to see how these wheels work.Why do bacteria use these 'corkscrews' to get about when larger animal cells use different propulsion systems (they may crawl like the amoeba or use beating hairs called cilia or lash a long whip-like flagellum which does not rotate as does the flagellum in bacteria but lashes from side-to-side)? Other bacteria are diffusion limited, so can only acquire nutrients that diffuse to them.The largest heterotrophic bacterium is the 80 by 600-micrometre large Epulopiscium spp.
Well, when one is as small as a bacterium, water starts to behave oddly - it becomes thick and sticky (it has a high relative viscosity due to the system having a very low Reynold's number) so the bacterium is effectively swimming through treacle. In this way gene expression can be regulated - DNA that is too compacted can not be read and is switched off.In Bacillus subtilis and Escherichia coli new-born cells have a single chromosome. Bacteria do not have the sophisticated machinery that causes cytoplasm to flow rapidly in plant and animal cells. Now imagine trying to swim through treacle with a paddle, push it to the left and you move forward a bit, but push it back to the right and you move backwards a bit - in short you get nowhere, you just oscillate about a bit!This does not happen in water because the water flows away, so you are not pushing the same water backwards and forwards.
Most bacteria multiply asexually by binary fission - a cell grows larger and then splits or divides into two new cells.
This mixing of the cytoplasm and active transport of materials within it allows animal and plant cells to obtain a larger size. Within these communities the bacteria communicate with each other and work together, however they remain separate as they do not generally form contact junctions with one another (as cells do in an animal or plant body) – it is rather like many separate organisms working together as a single organism.
Bacillus subtilis, Escherichia coli, Salmonella typhimurium;2) spherical (coccoid), bacteria with this shape are called cocci (sing.
In elongated cells this division is almost always occurs perpendicular to the long axis (see bacterial growth). In these biofilms, slime towers (microcolonies) shed swarmer cells into the water stream above. Reverse the motion of someone swimming with a paddle and you can tell the difference because they go backwards! These bacteria form multicellular filaments several cm long, allowing them to penetrate the 500-micrometre thick diffusive boundary layer and reach water containing the oxygen or nitrate electron acceptor. Some bacteria develop to the nextstage of multicellularity and form chains of cells (filaments) in which neighbouring cells may communicate with each other using electrical signals through special junctions. During replication the double-stranded 'ladder' of the DNA molecule unzips and the exposed single-strands act as templates against which new single-stranded DNA is synthesised.
When fluid flows over a solid surface, friction or drag with the surface creates a layer of fluid that is essentially stationary, this is the boundary layer. Some form minute fungus-like structures with fruiting bodies emerging from a sheet of cells to release spores.
Now, to move forwards a swimmer has to break this time-reversal symmetry so that the video looks different when played backwards. This  is semi-conservative replication, meaning that each new double-stranded daughter chromosome contains one strand from the old parent DNA molecule (the template strand) and one newly synthesised strand.
Molecules move in and out of the boundary layer predominantly by diffusion rather than by convection.
A corkscrew is ideal for this, because a corkscrew is twisted either clockwise or anticlockwise. These bacteria may also store several months reserve of nitrate and sulphur.Materials moving into and through the bacterium by diffusion must be metabolised by enzymes. These cells adhere to one-another to form microcolonies comprising square sheets (about 40 by 40 micrometres) which float in the water column. Reverse a corkscrew and it does make a difference - try turning the corkscrew in the opposite direction next time you open a bottle of wine.
This shape probably enhances the interception of light utilised by these organisms.7) A variety of other shapes also occur.
Animals and plants have linear DNA molecules and synthesis is different from that in the circular DNA of bacteria.
Each enzyme catalyses one or a few specific reactions and the molecules that the enzyme acts upon, and changes in some way, are called the substrate of the enzyme. Now, by using corkscrew-like engines the bacterium overcomes the problem of its tiny size which makes water behave like treacle, and it easily ploughs forward.Before I get into more technical details of these rotary engines, let me just stress the importance of bacteria. In the circular DNA of bacteria, replication always begins at a specific location on the DNA called the Ori (origin of replication) and proceeds from the Ori around the DNA in both directions, ending at another specific location called the terminus.
Most people think of them as germs, but the vast majority are not only harmless to humans, but beneficial. The Earth's ecosystems would grind to a halt without bacteria, in fact bacteria are the foundations of life on Earth, kill everything else but the bacteria and life continues, kill all the bacteria and the Earth dies. As DNA synthesis proceeds from the Ori, the daughter Oris move to opposite poles of the cell, so when division occurs each new daughter cell will have one chromosome with the Ori at one cell pole and the terminus at the other.
These reactions are of two general types: catabolic reactions break molecules down, whilst anabolic reactions build molecules up. Bacteria recycle nutrients into the biosphere, they break-down dead animal and plant remains and do all sorts of wonderful chemistry.
Not all bacteria exhibit the same pattern, for example in Caulobacter crescentus swarmer cells, the replisome assembles at the Ori at one cell pole. Thus, molecules can move through the entire volume of the cell many times during one round of catalysis (one round of enzyme action). Examples include most bouts of food-poisoning, tuberculosis, syphilis, hospital superbugs and others. As synthesis proceeds the Ori of one daughter chromosome stays put as the other moves to the opposite pole of the cell and the replisome moves to the centre of the cell as replication proceeds to the terminus. The traffic time is the theoretical time taken for any two molecules within a cell to meet. However, the end result is generally the same - DNA duplicates once per cell cycle so that each daughter cell contains one chromosome with the Ori at one cell pole and the terminus at the other.
In one second it is probable that any substrate molecule will have met any enzyme molecule. Viruses, fungi, worms and other organisms also cause many diseases.Killing all bacteria on Earth is easier said than done of course! Vibrio cholerae has two chromosomes, one of which replicates in a similar manner to that of Caulobacter crescentus, the other has its Ori situated in the centre of the cell.Chromkinesis, the movement of chromosomes around the cell is well coordinated. In large prokaryotes, about 100 micrometres long, the traffic time (which is proportional to the cube of cell length) is about 10 hours. Bacteria are extremely tough, partly because they can reproduce so rapidly, the fastest double their number every 10-20 minutes in optimum conditions, and partly because they are so adaptable - they evolve rapidly when they need to.Did you know?If a single bacterium (weighing ~10^-15 kg) doubled every 20 minutes, then the total population of bacteria would weigh the same as about 10 000 Earth's after two days! This may result in regional differences within the cell, or nonbounded compartmentalisation. Clearly this does not happen in Nature because conditions for bacterial growth are seldom optimum - the bacteria may run out of food for one thing.The appearance of superbugs that are resistant to almost every known drug is testament to the ability of bacteria to undergo rapid genetic changes and evolve and adapt to changes in their environment.
Although not as complex as the cytoskeleton of a plant or animal cell, the bacterial cytoskeleton is nevertheless important.


In other words, this is not a problem since the cells are narrow, but each section of the cell will be mixing and reacting, but molecules at each end of the cell will seldom meet and react with one-another.As well as problems transporting materials within the cell, there are problems in getting nutrients to the cell from outside.
Hard to visualise by standard electron microscopy it was a long time before it was realised that bacteria even have a cytoskeleton.
The viscosity of water dampens fluctuations smaller than the Kolmogorov scale or viscous length, which is about 1 to 6 mm. Humans often boast at how their nuclear weapons could sterilise their planet, but they can't, they would just kill all the big creatures like humans.
Sometimes it pays to be small - smaller creatures require fewer nutrients and so can reproduce rapidly.
At least one component of the cytoskeleton is responsible for positioning the chromosomes in the cell. Cells less than 100 micrometres in diameter are always surrounded by a diffusion sphere that is not affected by the surrounding turbulence and hence turbulence is not locally important for substrate flux to the cell. Bacteria grow so fast because they are small and so can easily absorb nutrients and get the food to all their parts, in contrast, larger animals require complex circulatory systems (heart and blood) and this limits the rate at which food can be absorbed. The tubular protein MreB forms spirals along the length of the cell, lying just beneath the inner cell membrane, and is involved in pulling the Oris apart during replication (and also guides the growth of the peptidoglycan cell wall). In other words, they are surrounded by a boundary layer of still water that does not easily mix with water further from the cell. The protein FtsK, part of the divisosome, also pumps DNA away from the forming cross-wall which will complete division of the cell into two. The minimum size of a cell to achieve an increase in substrate transport by swimming is about 10 micrometres. Note that we are talking here about mixing fluid, small bacteria can still obtain more food by swimming towards it, a different process (see chemokinesis).Thiovulum majus is an exception. It is a large sulphur-bacteria (about 8 micrometres in diameter, rang from 5 to 25 micrometres, which is very large for a bacterium indeed!). Their large size and high swimming speed enable them to overcome Brownian displacement and undergo directional swimming. This is an important point - almost all bacteria capable of motility can only locate food by altering their turning frequency, a process classically called chemokinesis, which statistically greatly increases their likelihood of locating food (see chemokinesis).
They are unable to swim straight to the source of food, a process called chemotaxis, because they are too small to discern the direction to the food source (they can not measure the concentration difference of nutrients detected at each end of the cell).
Larger cells can use stereoreceptors to tell them whether or not the chemical 'smells' strongest to the left or right and so turn straight towards the source. They call chemokinesis, a change in turning frequency, chemotaxis and refer to changes in speed as chemotaxis. These bacteria maintain their position by U-shaped swimming patterns, they swim and rotate in a helical path (3-10 rps, r = 5-40 mm, pitch = 40-250 mm).
Microbial respiration in the surface sediment establishes a steep oxygen gradient across this diffusive boundary layer (DBL). The mean oxygen diffusion time through the DBL is several minutes and there is diffusion limited transport (that is transport across this layer requires slow diffusion). Filaments or chains of bacterial cells can reach past this boundary layer, to access nutrients and oxygen.
It becomes overgrown by chemoautotrophic, symbiotic sulphur-oxidising bacteria (hitching a ride to get past the boundary layer).
In this enlarged condition, only 2% of the cytoplasm is active, the rest is occupied by a large vacuole.
Thiomargarita namibiensis is about 150 to 200 micrometres wide, but can be up to 750 micrometres. The large colourless sulphur bacterium Achromatium oxaliferum ranges from stores calcium carbonate and sulphur. Big bacteria are found on the sea floor, where there is a large hydrogen sulphide production and store sulphur for periods of less active volcanic sulphide venting and can also utilise nitrate as an alternative electron acceptor (see energy systems). Some grow on mobile animals, such as polychaetes, ostracods and mayfly larvae, in sulphide rich environments.Multicellular BacteriaMost bacteria form multicellular structures, called biofilms, over solid surfaces at some stage in their life-cycle. The bacteria communicate with one-another to build these slime structures and in this state they are more resistant to noxious agents such as antibiotics. Importantly, they can form tower-like structures, about 300 to 400 micrometres long from which they release swarmer cells, in a spore-like manner, above the stagnant boundary layer where they can be dispersed by convection.
However, although these structures are multicellular, they are not true multicellular organisms, but rather multicellular societies.
In almost all biofilms, the bacteria are never in intimate contact with one-another and do not communicate directly through special electrical contacts as do cells in a tissue.Bacterial filaments, chains of cells, can grow up to 7 cm in length. In magnetotactic forms, there are intercellular connections (microplasmodesmata) between 10-30 cells for coordination of locomotion.
Elecrical currents are thought to pass between the cells, through these connections, so that they all move in the same direction at the same time.
Connections such as these are the defining feature of true multicellular organisms (animal cells form gap junctions, plant cells plasmodesmata).
Some cyanobacterial filaments have similar connections, as do some other filamentaous bacteria, including strange forms seen in Antarctica.
They require both molecules, but can only tolerate low oxygen concentrations, since they are unable to breakdown toxic hydrogen peroxide that forms at higher oxygen concentrations. These bacteria move by gliding over solid surfaces and exhibit a phobic response to oxygen concentrations above about 5% air saturation - that is they move away to avoid such 'high' oxygen concentrations.
When cells at the filament tips encounter oxygen concentrations above the threshold they retreat, whilst the rest of the filament still glides upwards and as a result the middle part of the filament is forced out to one side at the oxic-anoxic interface, forming loops.
In light the benthic diatoms and cyanobacteria produce oxygen as a by-product of photosynthesis, which is toxic to Beggiatoa.
However, at night, organisms continue to respire and use up oxygen whilst none is made by photosynthesis, and this causes the oxygen – sulphide interface to move above the sediment.
With passing clouds and changing light levels, the filaments move up and down to track their optimum environment.Filament gliding movements ensures that the bacteria can break through the diffusiffive barrier or boundary layer, even if this boundary thickens. When oxygenated water flow decreases filaments move upwards and when oxygenated water flow decreases the filaments move downwards.Beggiatoa cells are 5-23 micrometres in diameter and contain sulphur inclusions.
In eutrophic coastal waters, for example fjords, an anoxic bottom layer of water forms during summer. Nitrate can be utilised, instead of oxygen, as an alternative electron acceptor for sulphide or sulphur oxidation. Nitrate can also penetrate up to 4 cm into the substrate (compared with only several mm for oxygen). Hydrothermal-vents, hydrocarbon seeps and methane hydrates have high sulphide concentrations and here form mats of unusually large Beggiotoa cells (each cell 40-200 micrometres in diameter!) presumably filled with sulphur reserves. These enlarged cells contain nitrate accumulated in a central vacuole at a concentration up to 160mM.
Pulsating hydrothermal emissions produces  water flow through the porous spaces in the mats. The cells stored reserves carry the cells over the periods in-between the intermittent pulses.Thiovulum majus is a highly motile, spherical bacterium whose biofilm forms a veil over the sediment surface.
Chemoautotrophs can fix their own carbon, but rely on chemical energy to do so rather than light.
The threads stick together and spread-out to form a 2D mesh containing 100 thousand to one million cells per square centimetre. This mesh separates the flowing oxygenated seawater above from a stagnant boundary layer of hydrogen sulphide enriched water, hence the veil creates its own diffusive boundary layer suspended in the water column. The outflows are channeled through numerous small openings in the veil, which has a fine lace appearance. The Péclet number for oxygen is about 40, in this system, and therefore convection dominates oxygen transport. When oxygen concentrations exceed 10% air saturation, these organisms retreat into their slime sheaths.
When up in the water column these bacteria fill their nitrate reservoirs and when down in the sediment they oxidise sulphide and store sulphur.
In high sulphide concentrations, the filaments leave their sheaths and live as freely gliding filaments on the sediment surface.Thiomargarita namibiensis is non-motile and the largest known sulphur bacterium. These cells only contact nitrate and oxygen when the loose sediment is suspended in the water column following storms, wave pumping or methane eruptions.
They can respire for 40-50 days or more without taking up new nitrate (for over two years in a cold room).



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24.10.2014, author: admin


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