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The bacteria are the sole members and they are the most abundant micro-organisms. The bacteria occur almost everywhere and present in a handful of soil.

They also live in extreme habitats such as hot springs, deserts, snow and deep oceans and many of them live in or on other organisms as Parasites.

Habitat

. Sole members are Bacteria.
. Most abundant micro-organisms.
. 100s of then in a handful of soil.
. Extreme habitats where few life from survive.

Shape:

. Spherical ----> Coccus (Cocci)
. Rod Shaped ---> Bacillus (Bacilli)
. Comma shaped -> Vibrium (Vibrio)
. Spiral -------> Spirillum (Spirilla)

Size:

0.15 – 1.5 micrometer (diameter)
1.00 - 20 micrometer (length)

Smallest Bacteria : Dialister pneumosintes (0.15 micrometer)
Largest Bacteria : E.fishelsonil (0.3 micrometer)
Longest Bacteria : Spirillum laidlow (15 micrometer)

Weight: 2 picometer

Structure: Very simple

Archaebacteria

These bacteria live in some harsh habitats such as highly salty areas (halophiles), hot springs (thermoacidophiles) and marshy areas (methanogens). Archaebacteria differ from other bacteria because they have a different cell wall structure.

This characteristic is responsible for their survival in extreme conditions. Methanogens are present in the intestines of many ruminant animals such as buffaloes and cows.

They are responsible for the production of methane (biogas) from the dung of these animals.

Eubacteria

Eubacteria or Truebacteria are a variety of bacteria characterized by the presence of a rigid cell wall and, if motile, a flagellum. Cyanobacteria have chlorophyll similar to green plants and are photosynthetic autotrophs.

Cyanobacteria are unicellular, colonial or filamentous, freshwater/marine or terrestrial algae. Colonies are usually surrounded by a gelatinous sheath.

They often bloom in polluted water bodies. Heterotrophic bacteria are most abundant in nature. The majority are important decomposers.

Many of them have a significant impact on human

They are helpful in making curd from milk, making antibiotics, fixing nitrogen in pulses.