Write a short note on Eubacteria.

(N/A) $\rightarrow$ Eubacteria: There are thousands of different eubacteria or true bacteria.
$\rightarrow$ They are characterised by the presence of a rigid cell wall and, if motile, a flagellum.
$\rightarrow$ Cyanobacteria: The cyanobacteria (also referred to as blue-green algae) have chlorophyll $a$ similar to green plants and are photosynthetic autotrophs.
$\rightarrow$ Habitat: The cyanobacteria are unicellular, colonial or filamentous, freshwater/marine or terrestrial algae. The colonies are generally surrounded by a gelatinous sheath. They often bloom in polluted water bodies.
$\rightarrow$ Function: Some of these organisms can fix atmospheric nitrogen in specialised cells called heterocysts, e.g., $Nostoc$ and $Anabaena$.
$\rightarrow$ Chemosynthetic autotrophic bacteria: These bacteria oxidise 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.
$\rightarrow$ Heterotrophic bacteria: These bacteria are the most abundant in nature. The majority are important decomposers. Many of them have a significant impact on human affairs. They are helpful in making curd from milk, production of antibiotics, fixing nitrogen in legume roots, etc. Some are pathogens causing damage to human beings, crops, farm animals, and pets. Cholera, typhoid, tetanus, and citrus canker are well-known diseases caused by different bacteria.
$\rightarrow$ Reproduction: Bacteria reproduce mainly by fission.