Bacteria from the outside in
What do bacteria look like?
"Morphology" describes the shape, size and arrangement of microbial cells. By viewing bacteria in the light microscope, you can easily see a cell's morphology. While there are certainly variations on the theme, bacteria generally fit into one of the shapes shown below:
Clustered cocci |
Rods |
Spiral-shaped |
Appendaged (Courtesy of William C. Ghiorse) |
While a "typical" bacterial cell is usually abut 1 x 3 um in size, bacteria range from 0.1 um to 2.0 um in width to 100 um long. The amazing exception is a bacterium called Euplopiscium fishelsoni, which is 50-100 um in width and over 500 um long. This bacterium can even be seen with the naked eye! Most bacteria are very small compared to eukaryotic cells (which range from 2 to 200 um wide). But compared to viruses (which range in size from 0.02 to 0.2 um), bacteria are very large indeed.
Cells can be arranged in many different ways. This arrangement is not at all random, but is a consequence of the cell's physiology, For example, some cells divide is such a way as to form clusters, chains or aggregates (see below). Some bacteria (namely the coryneform or "snapping" bacteria) divide in such a way to produce characteristic "v"-shaped cells.