Groupings of organisms based on similarities and relationships
Compared to many other organisms, bacteria as a group show the most extensive metabolic diversity
Bacteria
Some are autotrophic (synthesise their own food from inorganic substrates)
The vast majority are heterotrophs (depend on other organisms or dead organic matter for food)
They may be photosynthetic autotrophic or chemosynthetic autotrophic
Archaebacteria
Special bacteria that live in harsh habitats like extreme salty areas (halophiles) and hot springs (thermoacidophiles)
Differ from other bacteria in having a different cell wall structure which allows their survival in extreme conditions
Methanogens are present in the gut of ruminant animals and produce methane
Eubacteria (true bacteria)
Characterised by the presence of a rigid cell wall, and if motile, a flagellum
Cyanobacteria (blue-green algae) have chlorophyll a and are photosynthetic autotrophs
Cyanobacteria can be unicellular, colonial or filamentous, and often form blooms in polluted water bodies
Some cyanobacteria can fix atmospheric nitrogen in specialised cells called heterocysts
Chemosynthetic autotrophic bacteria oxidise inorganic substances and use the released energy for ATP production, playing a role in recycling nutrients
Heterotrophic bacteria are most abundant in nature and include important decomposers, as well as those helpful in making curd, producing antibiotics, and fixing nitrogen in legumes
