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What are bacteria?

Bacteria are a successful and ancient form of life, quite different from the eukaryotes (which includes the fungi, plants and animals). They are small cells, found in the environment as either individual cells or aggregated together as clumps, and their intracellular structure is far simpler than eukaryotes. Bacteria have a single circular DNA chromosome that is found within the cytoplasm of the cell as they do not have a nucleus. Indeed they lack any of the intracellular organelles so characteristic of eukaryotic cells, such that they do not have the golgi apparatus, endoplasmic reticulum, lysosomes nor mitochondria. However they are generally capable of `free-living' and therefore they possess all the biosynthetic machinery that is needed for this, including 70S ribosomes (as opposed to the larger 80S forms found in eukaryotes) distributed throughout the cytoplasm. The most complex region of the cell is often the cell surface. The cell wall / outer membrane is described below, but in addition some bacteria may secrete a polysaccharide capsule onto their outer surface, some may have flagella which they require for mobility and some may have external projections such as fimbriae and pili which are useful for adherence in their chosen habitat. Although bacteria are generally far simpler than eukaryotic cells, they are extremely efficient within their own little niche - and this may include the ability to cause human infections. Bacteria multiply by binary fission and there is no sexual interaction.

There are bacteria living in every habitable nook and cranny of the Earth. There are one hundred thousand of them squirming around on every square centimeter of your skin. Each drop of saliva has millions of bacteria in it. Yes, even your saliva, Mom.

The oceans are filled with bacteria. Each gram of dirt can have as many as two and a half billion bacteria in it. Bacteria have been found four miles below the Earth's surface. There's sketchy evidence for small bacteria floating twenty five miles up in the stratosphere, racking up microscopic frequent flyer miles. Scientists estimate that the total mass of the Earth's bacteria outweighs all of the plants and animals and all other living things combined.

If a nuclear war wiped out civilization, most of the Earth's bacteria wouldn't be affected.

If all of the water was sucked out of your body, ten percent of what was left, by weight, would be bacteria

Strange facts and Bacterial Records
Bacteria really are found everywhere, from the tops of the highest mountains to the bottom of the deepest oceans. In fact, some bacteria live way below the earth's surface with many species inhabiting coal measures and subterranean aquifers.

The record for underground living goes to a species of Chemolithotrophic bacteria found in Basalt deposits 1500m (4700ft) underground in solid rock. This really is solid rock, scientists only learned about these bacteria when drilling for oil. Checking drill cores brought up from these depths for signs of oil the found living bacteria.

The Sky
The air is full of bacteria. This is not surprising, when you realise that they are so small you cannot see them with your naked eye it is not hard to accept that they should get blown around easily. However it is not just surface bacteria getting caught up in the breeze. Recent discoveries have shown that some bacteria spend their whole lives in the atmosphere, growing and reproducing in the clouds above our heads.

On Ice
Bacteria are not as common in the extreme cold but they are there. Scientist know of bacterial species that live all their lives in the ice of glaciers and other bacteria have often found in the snows of the North and South poles Until recently sientists had thought bacteria found in these latitudes were just blown there by the winds but in 2000AD they proved that some of these species are different to any others and live at the North pole all year round where the temperature varies between -17 and -85 degrees C. BRRRRRRR .

Not So Cool
Not all bacteria like it cool, in fact some like it very hot. Hot springs occur all around the world and where ever they do Bacteria have learned to live in them. Some species are happy at 75 C while others think even this is cool. Species of Aquifex can live in water as hot as 95 C, this is just 5 degrres away from the boiling temperature of water. This is not the world record though, that belongs to a species of Archaea which is happy to grow in water around deep sea hydrothermal vents at temperatures as high as 106 C (at these great depths, several miles down, the pressure stops the water from boiling and keeps it liquid).
The Deep Sea
Anyone who has dived down into the water and felt their ears pop knows that the pressure that water exerts increases the deeper you go. Humans cannot go more than a few tens of metres down without protecting their ears and several hundred metres starts to cause potentially lethal problems, even for experienced divers. The oceans however are not hundreds, but thousands of metres deep and the pressure increases by the equivalent of 1 atmosphere every ten metres down. Thus bacteria which live at depths greater than 10000 metres must be able to survive pressures in excess of 1000 times the air pressure at sea level. These bacteria are called 'Extreme Barophiles'. Species that thrive at these depths are so biologically different from sea level bacteria that they cannot function properly at pressures less than 400 atmospheres and die in a couple of hours if brought to the surface.

How Small??
Bacteria are small, on average most species of bacteria have diameters of 0.5 to 2.0 microns. Obviously, though diameter gives you a good indication of the size of a spherical cocci bacterium you need to know its length as well if it is a rod (cylindrical) bacterium. The smallest bacterium have sizes down to 0.1 - 0.2 microns. Looking at it the other way, there is a giant bacterium found in Sturgeon fish. This bacterium called Epulopiscium fishelsoni is over 0.5 mm long.

Species Size in Microns
Epulopiscium fishelsoni 600x50
Bacillus megterium 4x1.5
Escherichia coli 3x1
Streptococcus pneumoniae 0.8x0.8
Haemophilus influenzae 1.2x0.25
Rhodospirillum photometricum 30x3
Chromatium buderi 7x4

Lions and leopards have been known to attack and kill humans, but it's the tiger who earned the label "man-eater", and nowhere are their attacks more prevalent, than in India.

From 1902-1910 the country recorded an average of 851 deaths due to tiger attacks, but in 1922, there was a whopping 1603. One tiger, from the Champawat area, was reputed to have killed 434 people by itself, before being shot. However, given the higher population of the animals back then, and the fact that they attack from behind, it's questionable whether it was the same animal.

The tiger will not normally stalk human prey. In fact, they are a somewhat lazy hunter, following potential victims from behind and then making a rush to leap on their backs. But if they miss, they seldom pursue their lost meal.

Their normal diet is comprised of larger animals like young buffalo, who are brought down either with a bite to the back of the neck, or by knocking them down, and then grabbing them by the throat until the animal suffocates. This has the benefit of keeping the tiger out of the way of horns and hooves, as well.

Once the prey is down, the tiger will start dining, eating up to 85 lbs. of meat at a time. If the kill is undisturbed, they will return to it for 5-6 days until it is gone. This means that a major kill is only made every 6-8 days, depending on the family unit.

A tiger hunts alone, but they have been observed with family members all hunting in the same area. Actual kills in the wild are rarely observed by researchers, who base much of their data on the tiger's attack habits, by studying tethered prey.

For many animals that don't practice parental care, growing up is a very risky proposition. You start out very small, which exposes you to predation by a host of animals. Due to your large surface-to-volume ratio, you're also more prone to drying out, absorbing toxic levels of pollutants, etc. And mommy and daddy aren't there to protect you. To compensate for your low probability of reaching maturity, your parents also gave you a multitude of siblings, with which you may have to compete for food. (Sound familiar? This is Darwin's "struggle for survival.")

As if growing up isn't hard enough, some species also face tremendous time pressure to do so. For example, many amphibians lay their eggs in temporary ponds or puddles, requiring the hatching larvae to grow and metamorphose into terrestrial adults (frogs, toads, or salamanders) before their first home dries up. And to make it a real crapshoot, there's no way of predicting how long they'll have or how much competition for resources they'll face. If the spring is dry, the pond may dry up before any adults emerge. And if many females lay their eggs in the same pond, competition for food such as algae and detritus may be so intense that growth and development rates are slowed, so none may mature in time even in a normal spring.

To increase the odds that at least some individuals mature even in years when resources are scarce due to overpopulation (i.e., when the population greatly exceeds its carrying capacity), a few amphibian species have evolved a novel strategy. Basically, a small number of individuals develop into cannibals! Not only do they acquire a taste for their own species' flesh, but they also develop into a distinctly different "morph" (form). Cannibal morphs have larger heads and bigger teeth that make them better at capturing and consuming their own kind. This process has been extensively studied in the spadefoot toad (Scaphiopus spp.) and tiger salamander (Ambystoma tigrinum). One curious finding is that becoming a cannibal is not genetically programmed, but brought on by an environmental cue such as crowding. So the cannibals differ phenotypically but not genotypically from the "normal" herbivorous or omnivorous morph. Also, cannibals can identify their own brothers and sisters, preferentially feeding on other families' members if given the chance.

The benefits of this strategy are obvious. Not only is the resource base available to these lucky cannibals increased (and, by virtue of being biochemically identical, species-mates are also highly nutritious), but the number of their competitors is decreased. This brings the population below carrying capacity, speeding growth and development and increasing the chance of maturing in time. As a result, the population becomes more stable as well. Is there a downside to this behavior? Eating your own kind may make you more likely to acquire diseases [] from your food than if you eat more distantly related species. This is because conspecifics are more likely to carry diseases to which you are ...

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