Bacteria Types

Bacteria refer to single-celled microscopic organisms. Bacteria exist in a variety of shapes and sizes. They are measured in micrometers (a millionth part of meter). These tiny organisms can be found anywhere in the environment. Before the advent of DNA sequencing, bacteria were classified on the basis of their sizes–a technique called morphology. Today, both techniques are followed–i.e., morphology and DNA sequencing–to classify a bacterium. Several other factors are also taken into account in bacterial classification. These are metabolic activities, habitat, biochemical nature and antigenic qualities.

Types Based on Shapes

Bacteria are classified on the basis of biochemical properties and shapes. There are three primary shapes–i.e. spherical-, rod-, and spiral-shaped bacteria. Rod-shaped bacteria (e.g., Bacillus anthracis) are known as bacillus while spherical (e.g., Staphylococcus aureus) and spiral types (e.g., Vibrio Cholerae) are called coccus and spirillum, respectively.

Aerobic and Anaerobic Bacteria

Another way of classifying a bacterium is assessing it through its oxygen requirement for survival. Bacteria that require oxygen for survival are aerobic bacteria (e.g., Mycobacterium tuberculosis), and those which do not need oxygen for survival are classified as anaerobic bacteria (e.g., Clostridium tetani).

Gram-Positive and Gram-Negative Bacteria

One classification is based on the Gram’s stain through which an agent is utilized to bind to the bacteria’s cell wall. Gram’s stain is a method for the differential staining of bacteria by treatment with a watery solution of iodine. The bacteria that hold the purple dye when stained by Gram’s stain are gram-positive bacteria (e.g., clostridium) while Gram-negative bacteria (e.g., Pseudomonas) do not hold the purple dye of Gram’s stain.

Autotrophic and Heterotrophic Type

Bacteria are also classified based on the growth and reproduction patterns. Autotrophic bacteria receive carbon from atmospheric carbon dioxide and prepare own food in the form of organic molecules (glucose) in the presence of sunlight. Heterotrophic bacteria require complex organic compounds of nitrogen and carbon for metabolic synthesis, which they obtain from plant or animal matter.

Phylum Classification

A major bacteria classification is known as phylum that is not only based on morphology but also on DNA sequencing and biochemistry. According to phylum, bacteria are differentiated into 16 groups–i.e., Aquificae, Xenobacteria, Chrysogenetes, Thermomicrobia, Cyanobacteria, Chlorobia, Proteobacteria, Firmicutes, Planctomycetes, Spirochaetes, Fibrobacter, Bacteroids, Flavobacteria, Sphingobacteria, Fusobacteria and Verrucomicrobia.

This classification also differentiates the bacteria according to their natural habitats such as ocean water, sweet water, extreme weather conditions (too hot or cold), high acidic or alkaline atmosphere, and radioactive fields. Some bacteria are also fond of nestling in moist places.

About this Author

Steve R. Kevin has been involved in the medical science article industry for more than six years. He is a Maryland-based writer focusing on neuroscience articles. His articles have been published in PLoS Medicine. He also holds a Doctor of Philosophy in neuroscience from the University of Maryland.