Scientists use various systems for classifying bacteria into different types. One of the simplest systems is by shape. Other systems depend on oxygen use, source of carbon, and response to a particular dye.
Classification by shape
Most bacteria come in one of three shapes: rod, sphere, or spiral. Rod-shaped bacteria are called bacilli. Spherical bacteria are called cocci, and spiral or corkscrew-shaped bacteria are called spirilla. Some bacteria come in more complex shapes. A hairlike form of spiral bacteria is called spirochete. Streptococci and staphylococci are well-known disease-causing bacteria among the cocci (Betsey, 2003).
Aerobic and Anaerobic Bacteria
Scientists also classify bacteria according to whether they need oxygen to survive or not. Aerobic bacteria require oxygen. Anaerobic bacteria cannot tolerate oxygen. Bacteria that live in deep ocean vents or within Earth are anaerobic. So are many of the bacteria that cause food poisoning.
Autotrophic and Heterotrophic Bacteria
All bacteria require carbon for growth and reproduction. Bacteria called autotrophs (“self-feeders”) get their carbon from CO2. Most bacteria, however, are heterotrophs (“other feeders”) and derive carbon from organic nutrients such as sugar. Some heterotrophic bacteria survive as parasites, growing within another living cell and using the nutrients and cell machinery of their host cells. Some autotrophic bacteria, such as cyanobacteria, use sunlight to produce sugars from CO2. Others depend instead on energy from the breakdown of inorganic chemical compounds, such as nitrates and forms of sulfur (Betsey, 2003).
Gram-Positive and Gram-Negative Bacteria Another system of classifying bacteria makes use of differences in the composition of cell walls. The difference becomes clear by means of a technique called Gram’s stain, which identifies bacteria as either gram-positive or gram-negative. After staining, gram-positive bacteria hold the dye and appear purple, while gram-negative bacteria release the dye and appear red. Gram-positive bacteria have thicker cell walls than gram-negative bacteria.........
