- Bacteria are the sole members of the Kingdom Monera.
- Bacteria are grouped under four categories based on their shape
- spherical Coccus
- rod-shaped Bacillus
- comma-shaped Vibrium
- spiral Spirillum.
Fig. Categories of bacteria
- Bacteria are divided into two major groups
- They live in some of the most harsh habitats such as extreme salty areas called as halophiles, hot springs and so, named as thermoacidophiles, marshy areas and hence, named as
- The can survive in extreme habitats due to a different cell wall structure.
- Methanogens are present in the guts of several ruminant animals and they are responsible for the production of methane (biogas).
- Eubacteria are known as true bacteria, and are cauterized by the presence of a rigid cell wall, and if motile, a flagellum.
- The cyanobacteria or blue-green algae have chlorophyll a similar to green plants and are photosynthetic autotrophs.
- The cyanobacteria are unicellular, colonial or filamentous, marine or terrestrial algae, and the colonies are generally surrounded by gelatinous sheath.
- Some of the cyanobacteria can fix atmospheric nitrogen in specialized cells called heterocyst. For example- Nostoc and Anabaena.
Chemosynthetic autotrophic bacteria oxidize various inorganic substances such as nitrates, nitrites and ammonia and use the released energy for their ATP production.
- Heterotrophic bacteria are important decomposers.
- They are helpful in making curd from milk, production of antibiotics, fixing nitrogen in legume roots.
- Some are pathogens causing damage to human beings, crops and cause cholera, typhoid, tetanus to human being.
- Bacteria reproduce mainly by fission, or producing spores under unfavorable conditions or by a sort of sexual reproduction transferring DNA from one bacterium to other.
- The Mycoplasmas are organisms that completely lack a cell wall, and they are the smallest living cells known, which can survive without oxygen.