Different morphological characteristics such as size, shape, staining characterstics, flagellation etc are used to clas-sify the eubacteria.
Size – Bacteria are microscopic. Normally their diam-eter varies from 0.2 to 1.5 micron and length varies from 2 to 10 micron and the length of rod-shaped or bacillus bacteria varies from 0.3 to 15 micron. The largest bacterium is Baggiatoa mirabilis. It’s diameter is 16 to 45 micron and length is 80 micron or more.
Shape – On the basis of shape, the bacteria are of following types
1. Coccus or spherical bacteria-They are spherical and their diameter is 0.5 to 1.25 micron.
They are non- flagellated and are of following types
(i) Micrococci – Solitary
Example: Micrococcus agilis, Micrococcus aureus etc.
(ii) Diplococcus – Two or in pair
Example: Diplococcus pneumoniae
(iii) Tetracoccus – Four round cells
Example: Micrococcus tetragcnus Neisseria etc.
(iv) Streptococcus – They are chajn shaped
Example: Sireptococcus lacts
(v) Staphylococcus – Round and forn in grape – like clusters.
Example: Siaphylococcus aurcus
(vi) Sarcinae – Spherical bacteria
Example: Sarcina luteus etc.
2. Bacillus or Rod shaped bacteria
(i) Monobacillus – Single rod-like bacteria.
Example: Bacillum
(ii) Diplobacillus – Two rods arranged side by side with each other.
Example: Coryne bacterium diptherae
(iii) Streptobacillus – Rods arranged in chains.
Example: Bacillum iuberculosis
3. Spiral or cuboidal bacteria
They are spiral or helical shaped and flagellated.
Example: Spirillum minus, spirillum volutans.
4.Vibrio or coma
They arc curved-rod shape or comma shape and monoflagcllated.
Example: vibrio cholerae
5.Filanientous bacteria – They arc very long thin filament-shaped. Some of them form branching filaments
ExampIe: Beggiatoa. Cladothrix, Leptothrix etc.
6.Pleoniorphic bacteria – They are able to alter theirshape or size in response to enironrnental conditions.Hence. they are found m more than one form.
For example: Acetobactor. Minute or long rod(Bascillus) or chain of minute rods (Streptobacillus)