Bacteria

Actinobacteria

Groups and identification

[[image:bacteria_shape.png|right|framed|Bacteria come in a wide variety of shapes:A. Rod-shaped

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B. Round-shaped or spherical.

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C. Round-shaped in clusters.

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D. Round-shaped in twos.

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E. Spiral-shaped.

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F. Comma-shaped.]]

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Bacteria come in a variety of different shapes. Most are rod-shaped, sphere-shaped, or helix-shaped; these are respectively referred to as bacilli, cocci, and spirilla. An additional group, vibrios, are comma-shaped. Shape is no longer considered a defining factor in the classification of bacteria, but many genera are named for their shape (e.g. Bacillus, Streptococcus, Staphylococcus) and it is an important part in their identification.

Related Topics:
Bacilli - Cocci - Spirilla - Vibrio - Streptococcus - Staphylococcus

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Another important tool is Gram staining, named after Hans Christian Gram who developed the technique. This separates bacteria into two groups, based on the composition of their cell wall. The first formal grouping of bacteria into phyla was based largely on this test:

Related Topics:
Gram staining - Hans Christian Gram

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• Gracilicutes - bacteria with a second cell membrane containing lipids, giving them Gram-negative stains
• Firmicutes - bacteria with a single membrane and thick peptidoglycan wall, giving them Gram-positive stains
• Mollicutes - bacteria with no second membrane or wall, giving them Gram-negative stains

The archeabacteria were originally included as the Mendosicutes. As given, these phyla are no longer believed to represent monophyletic groups. The Gracilicutes have been divided into many different phyla. Most gram-positive bacteria are placed in the phyla Firmicutes and Actinobacteria, which are closely related. However, the Firmicutes have been redefined to include the mycoplasmas (Mollicutes) and certain Gram-negative bacteria.

Related Topics:
Firmicutes - Actinobacteria - Mycoplasma

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