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Eubacteria (“True Bacteria”)
- Characteristics:
- Rigid cell wall
- Flagellum (if motile)
- Cyanobacteria (Blue-Green Algae):
- Contain chlorophyll a (similar to plants)
- Photosynthetic autotrophs
- Forms: Unicellular, colonial, filamentous
- Habitats: Freshwater, marine, terrestrial
- Often form blooms in polluted water
- Some fix nitrogen in specialized cells called heterocysts (e.g., Nostoc, Anabaena)
- Chemosynthetic Autotrophs:
- Oxidize inorganic substances (nitrates, nitrites, ammonia) for energy (ATP production)
- Important in nutrient recycling (nitrogen, phosphorus, iron, sulfur)
- Heterotrophic Bacteria:
- Most abundant type of bacteria
- Roles:
- Decomposers
- Food production (e.g., curd from milk)
- Antibiotic production
- Nitrogen fixation in legume roots
- Pathogens: Cause diseases in humans, crops, animals (e.g., cholera, typhoid, tetanus, citrus canker)
- Reproduction:
- Fission: Primary mode of reproduction
- Spore formation: Under unfavorable conditions
- Primitive form of sexual reproduction: DNA transfer between bacteria
- Mycoplasma:
- Lack a cell wall
- Smallest living cells known
- Can survive without oxygen
- Many are pathogenic to animals and plants
