Classification of Bacteria

The classification of bacteria is determined on the basis of their form, structure, mode of nutrition, the environment they are living in or their habitat. Since bacteria are cosmopolitan and found everywhere on earth.

Classification of Bacteria

Classification of Bacteria is as follow:

  1. Archeobacteria

They are the most primitive organisms on the earth. The lack peptidoglycan in their cell wall. The live in the deep sediments of oceans.
Example: Methanogenic bacteria

Classification of Bacteria

Methanogenic Bacteria

  1. Actinomycetes

They form colonies of branching hyphae (tubular filaments resembling those of fungi). Reproduction takes place by fragmentation of the end of hyphae into spores. Most actinomycetes live in the organic litter of soil.
Example: Mycobacterium


  1. Chemoautotrophic bacteria

They obtain energy from oxidizing inorganic substances like NH3, NO3, and H2S. These bacteria are obligate aerobes. Thus, they are common in aerated soil.
Example: Nitrobactor


  1. Cyanobacteria

They are photoautotrophs with plantlike photosynthesis. They have chlorophyll a and two photosystems. Other accessory pigments are called pycoblins. They are typical blue-to-grayish-brown color. Cell walls are thick and gelatinous. Flagella absent.
Example: Anabaena, Nostoc, Oscillatoria


  1. Endospore Forming Bacteria

They are gram-positive bacteria. They have flagellated rods. They produce endospores. They are both obligate anaerobes and aerobes.

Example: Bacillus, Clostridium


  1. Enteric Bacteria

These. are gram-negative, facultative anaerobes. They undergo anaerobic respiration using NO3 as the electron donor. They inhabit the intestinal tracts of animals.

Example: Escherichia coli

Escherichia coli

  1. Mycoplasma

They are the smallest bacteria. They lack cell walls. They grow extracellularly. They are saprobes and animal pathogens.

Example: Mycoplasma


  1. Myxobacteria

They are soil-dwelling chemoheterotrophs. Individual cells move by gliding. The cells form fruiting body during dry season. Spores are released and grow into new colonies.

Example: Myxococcus


  1. Nitrogen Fixing Aerobic Bacteria

They are common free-living and mutualistic species. The genus Rhizobium lives in root nodules on leguminous plants. It fixes the atmospheric nitrogen.

Example: Azobacter, Rhizobium


  1. Phototropic Anaerobic Bacteria

They arc photoautotrophs. They have different photosynthetic equipment than plants. They use H2S as electron source. They are anaerobes. They are found in pond, lake, and ocean sediments. They have different groups like bacteria and the green sulfur bacteria.

Example: Chromatium














  1. Pseudomonads

They are present in nearly all aquatic and soil habitats. Their cells are rod-shaped with grain-negative cell wall. They are flagellated at one end. They are chemoheterotrophs

Example: Pseudomonas


  1. Rickettsias and Chiamydias

They are obligate intracellular parasites of animals. They have reduced gram-negative cell wall. Rickettsias alternate between arthropod and mammal hosts. They cause different diseases.

Example: Rickettsia Chlamydia

Rickettsia Chlamydia

  1. Spirochetes

They have helical cells. They sometimes become very long. They show corks screw like movement. They are free-living saprobes and parasites.

Example: Borrelia


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