ABSTRACT
Bacteria must have got something right. If the earth was formed approximately 4 to 5 billion (1109 million) years ago, it is estimated that bacteria appeared a billion years later (Figure 1.1), whereas, in relative terms, animals and plants have only just appeared. The diversity of bacteria is difficult to comprehend fully since it is estimated that around 90 per cent of all bacterial types have not yet been successfully grown in the laboratory. Microbiologists who concentrate on bacteria that interact with humans will encounter a tiny, specialist collection of organisms that is not representative of the tremendous variation that can be seen in more diverse environments. Bacteria have a variety of shapes, which presumably reflects the extreme range of habitats they occupy. Bacteria thrive at temperatures that range between below freezing and greater than the boiling point of water. Bacteria grow faster than all other organisms, and utilise a broad spectrum of chemicals as nutrient sources and energy sources. Yet, at the other extreme, under adverse conditions (for example, low available water and nutrient levels) bacteria have survival strategies of which the production of endospores yields the most resilient form.
