Comprehensive Study Guide on Eubacteria and Cyanobacteria

General Characteristics of Eubacteria

Eubacteria are distinguished as the "true bacteria" and are characterized by several definitive morphological features. A primary structural hallmark of this group is the presence of a rigid cell wall, which provides protection and maintains the cell's shape. The motility of Eubacteria is determined by the presence or absence of flagella; if flagella are present, the organism is classified as motile, whereas the absence of flagella renders the bacterium non-motile.

Cyanobacteria: The Blue-Green Algae (BGA)

Cyanobacteria, commonly referred to as Blue-Green Algae (BGA), are a major group of Eubacteria that function as photosynthetic autotrophs. These organisms contain $Chlorophyll \, a$, the same photosynthetic pigment found in green plants, enabling them to produce oxygen through oxygenic photosynthesis. In terms of morphology, Cyanobacteria can be unicellular, colonial, or filamentous. They are found across diverse environments, including freshwater, marine, and terrestrial habitats. When existing in colonial forms, they are typically surrounded by a protective gelatinous or mucilaginous sheath.

Nitrogen Fixation and Heterocysts

Within the group of Cyanobacteria, there are specific organisms capable of atmospheric Nitrogen ($N$) fixation. This process is carried out in specialized, thick-walled cells known as heterocysts, which provide an appropriate environment for the chemical reactions involved in converting nitrogen into a biological form that can be used for making food. Notable examples of bacteria that utilize heterocysts for nitrogen fixation include the genera $Nostoc$ and $Anabaena$.

Chemosynthetic Autotrophs and Nutrient Recycling

Beyond photosynthetic varieties, the Eubacteria domain includes chemosynthetic autotrophs. These bacteria do not rely on light energy; instead, they generate energy by oxidizing various inorganic substances. This energy-releasing process is crucial for the production of $ATP$ (Adenosine Triphosphate). Furthermore, chemosynthetic Eubacteria play a vital role in global biogeochemical cycles by facilitating the recycling of essential nutrients. They are specifically involved in the recycling of Iron ($Fe$), Sulphur ($S$), Phosphorus ($P$), and Nitrogen ($N$) within the environment.