Bacteria are divided into two groups based on the presence or absence of oxygen.
1. Aerobic Bacteria: Bacteria that cannot survive without the presence of oxygen are called aerobic bacteria. For example- Bacillus anthracis, Azobacter beijerinckii.
2. Anaerobic Bacteria: Bacteria that can survive without the presence of oxygen are called anaerobic bacteria. For example, Clostridium tetani.