Bacteria can be found in every envirnonment on earth, from oceans, lakes and ponds to deserts and around aquatic volcano vents, on mountains even other organisms. Bacteria may have been present for longer than any other organism on the planet- the oldest known fossils in the world are formed from blue-green algae, and have been found to be up to 3.5 billion years old.
The fundamental characteristic defining a bacterium is where the organisms genetic material is stored. In plants, animals and fungi, the DNA is stored in a membranous container inside their cells, which is termed the nucleus. Organisms which keep their DNA in nuclei (plural of nucleus) are termed eukaryotes. Bacteria, on the other hand, do not have their DNA contained in a nucleus, and are termed prokaryotes. Prokaryotes tend to be simple organisms- they are composed of one or a few cells only and are typically measured in micrometers (millionths of a metre)
Bacteria may be further classified according to a range of different characteristics, such as their physical shape, source of energy or even their sensitivity to magnets.
When bacteria are classified by shape, they can be termed either cocci (spherical), bacilli (rod shaped) or spirochetes (cork-screw shaped). If bacteria are classified according to their energy source, then they are termed either photoautotrophes (obtain their energy from the sun, like plants), chemoautotrophes (obtain their energy from inorganic chemical compounds, such as sulphides) or heterotrophes (obtain their energy by consuming other organisms, like animals).
Magnetotactic bacteria are classified by their reaction to magnetic fields - magnetotactic bacteria will move in a predictable way when exposed to one end (pole) of a bar magnet. Observations of magnetotactic bacteria in Western Australia so far have shown the existence of both "north-seeking" and "south seeking" bacteria. However the majority in any drop will tend to move northwards, all things being equal. "North-repelled" bacteria have also been observed in the same samples, and these tend to move away from a presented North pole. Fairly little is known of these magnetotactic bacteria. Do they somehow "learn" which way is north or do they inherit it when they separated from the previous bacterium during cell division? What would happen if a whole bunch of them were kept in a magnetically neutral environment for many generations? Would they still know north when they were let out?