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 and found living bacteria.
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.
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.
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|
Some bacteria can move. A few can glide across a surface and some aquatic species can control their buoyancy, and thus their depth in the water, through internal gas vesicles (bubbles). Most bacteria however move by means of one or more flagella (singular flagellum). A bacteria that possesses one or more flagella is termed 'flagellated' and there are 3 main different styles of flagellation. If the bacterium has just one or two flagella placed at either one, or both ends of its cell (this applies to rod and spirochaetic bacteria) it is said to have Polar Flagellation. A bunch of flagella coming from one end of the cell is called Lophotrichous flagellation (tufted) and if it the flagella come out at random points around the cell it is called Peritrichous Flagellation. The flagella are not straight but are twisted in a sort of wave shape. The distance between each wave crest or trough is fixed for a species and is often important in identification. Bacteria move not by flexing their flagella the way a fish flexes its tail and fins, but by rotating them like a propeller. This can enable them to obtain speeds as high as 0.00017 kilometres per hour. This may not seem very fast, but to put it into perspective remember that we are talking about very small organisms. Looked at another way, they are travelling at about 50-60 body lengths per second. This would be the equivalent of a 1.8 metre (6 feet) tall man running at 100 metres per second, 9 times faster than the world record. Cheetahs, are the fastest animals on land but even they only move at about 25 body lengths per second.
|Type of Flagellation||Bacterial Species|
|Polar flagellation||Rhodospirillum centenum|
|Lophotrichous flagellation||Rhodospirillum photometricum|
|Peritrichous flagellation||Salmonella typhi|
Bacteria do not only live in extreme environments, but like us they are found in their greatest numbers where the living is easy. Where it is warm and moist, with plenty of easily obtainable nutrients. Anywhere that dead and decaying matter is present is a good home for bacteria. So also is anything living. Bacteria live both on and in animals and plants. Every human being has a particular flora of bacteria that inhabit every surface of our bodies, on our skin, in our mouths, our stomachs and intestines etc. even in and around our genitalia (see The Human Body as a Bacterial Environment).
Bacteria are a major component of the unseen world of 'Micro-organisms' and as such they play a decisive role in the maintenance of life on this planet. This life is not a static process, instead it is a series of dynamic fluxes or flows. What is soil, becomes grass, becomes a cow, becomes you and me and then becomes soil again. Bacteria, and other micro-organisms are essentially important in the cycling of nutrients and energy, particularly in the breakdown of dead organic matter to make the resources locked up in things like dead trees available again to other living organisms. They also play a central role and the fixation of atmospheric Nitrogen into organic molecules and in the cycling of minerals such as Carbon and Sulfer. Further to this some bacteria also play an important role in trapping the suns energy so that it can be used by living organisms. Any cycle or system you look at has bacteria playing a crucial supportive role in it somewhere. Bacteria are an essential in the maintenance of these flows of energy and nutrients throughout our world. Without them the whole ecosystem would collapse.