What are the types of bacteria?

There are various groups of bacteria, which belong to same family and are evolved from same bacteria (ancestor). However, each types of bacteria posses its own characteristics (those which are evolved after separation from the original specie).

Classification of Bacteria:
Bacteria are mainly classified into phylums (phylum is a scientific classification of organisms). For simplification, bacteria can be grouped into the following groups:

Bacteria classification based on shapes:
As already mentioned, before the advent of DNA sequencing, bacteria were classified based on their shapes and biochemical properties. Most of the bacteria belong to three main shapes: rod (rod shaped bacteria are called bacilli), sphere (sphere shaped bacteria are called cocci) and spiral (spiral shaped bacteria are called spirilla). Some bacteria belong to different shapes, which are more complex than the above mentioned shapes.

Aerobic and anaerobic bacteria:
Bacteria are also classified based on the requirement of oxygen for their survival. Bacteria those need oxygen for their survival are called Aerobic bacteria and bacteria those do not require oxygen for survival. Anaerobic bacteria cannot bear oxygen and may die if kept in oxygenated environment (anaerobic bacteria are found in places like under the surface of earth, deep ocean, and bacteria which live in some medium).

Gram Positive and Gram Negative bacteria:
Bacteria are grouped as ‘Gram Positive’ bacteria and ‘Gram Negative’ bacteria, which is based on the results of Gram Staining Method (in which, an agent is used to bind to the cell wall of the bacteria) on bacteria.

Autotrophic and heterotrophic bacteria:

This is one of the most important classification types as it takes into account the most important aspect of bacteria growth and reproduction. Autotrophic bacteria (also known as autotrophs) obtain the carbon it requires from carbon-dioxide. Some autotrophs directly use sun-light in order to produce sugar from carbon-dioxide whereas other depend on various chemical reactions. Heterotrophic bacteria obtain carob and/or sugar from the environment they are in (for example, the living cells or organism they are in).