Eubacteria

• They are characterized by the presence of a rigid cell wall and a flagellum (if motile).
• They include Autotrophs (photosynthetic and chemosynthetic) and Heterotrophs.

a. Photosynthetic autotrophs (E.g. Cyanobacteria):

• They have chlorophyll-a similar to green plants.
• Cyanobacteria (blue-green algae) are unicellular, colonial or filamentous, marine or terrestrial algae.
• The colonies are generally surrounded by gelatinous sheath.
• They often form blooms in polluted water bodies.
• Some of these can fix atmospheric nitrogen in specialized cells called heterocysts, e.g., Nostoc and Anabaena.

b. Chemosynthetic autotrophs:

• They oxidize various inorganic substances such as nitrates, nitrites and ammonia and use the released energy for their ATP production.
• They play a great role in recycling nutrients like nitrogen, phosphorous, iron and sulphur.

c. Heterotrophic bacteria:

• They are the most abundant in nature.
• The majority are important decomposers.