Extreme bacteria - The Archaebacteria are generally found in environmental extremes (as far as we're concerned) in that they exist in hot springs at 100 degrees C (boiling water!), in the bottom of the ocean at ~110C and in water the density of lead, in saturated salt ponds and other environments that would seem to be inimitable to life. They can metabolize unusual substances for energy like methane, sulfur, and hydrogen gas. Their origin and relationship to Eubacteria and eukaryotes is currently being hotly debated among microbiologists. However, some of their biochemical characteristics resemble eukaryotes more than they do Eubacteria. Fortunately, there are no reports of any pathogenic Archaebacteria.
Eubacteria - There are an enormous number of Eubacteria species, with a bazillion new ones being discovered every time someone looks.
The size, shape and arrangement of the bacteria, is one method of identifying the many types. This characteristic is called their morphology. Bacteria come in a bewildering and exciting variety of morphologies.
Shape offers many advantages to the bacterium. The cocci shape is more resistant to drying than the rod, the rod has more surface area for nutrient absorption and the spirillum structure provides less resistance to movement. These shape differences are only superficial and mask many more important differences inside.
The Bacilli are rod-shaped (yellowish-green or light blue in the image above). The rods of the bacilli may be long, short, thick, thin, have rounded or pointed ends, or they may be thicker at one end than the other etc. The bacilli may be found mainly as single cells or as groups such as chains,
are round. Cocci
may be large, small, round or oval shaped to various degrees. Cocci also
are found as individuals or in various groups. Diplococci
are round bacteria that are found in twos (see the Cocci in the
are Cocci who remain joined after binary fission and form long "strings"
of bacteria, as in the image above. The
bacteria. These may be found as fat, thin, loose spirals or
very tight spirals.