Nitrogen

• Bacteria are the only organisms that fix nitrogen. Nitrogen compounds are needed by all living organisms in order to survive. These bacteria are kept in the roots of some plants such as bean plants.
  
  

Decomposition

• Like fungi, bacteria play a role in breaking up dead compounds, freeing them to become a part of the life cycle again.
  
  

Digestion

• Many animals rely on bacteria to break down the cell walls of plants, because digestive juices are unsuccessful in breaking down these tough walls.
  
  

Replacement Biotics

• Good bacteria often produce chemicals that damage or scare away harmful bacteria, allowing the good bacteria to have exclusive domain over an area.
  
  

Viruses

• Some bacteria produce hydrogen peroxide that can destroy harmful viruses.
  
  

Cancer

• Some bacteria protect animals from cancer by neutralizing nitrates that lead to cancer.