What are microorganisms like Azotobacter, Bacillus, Clostridium, and Rhizobium frequently referred to as?

Nitrogen fixers are known for their ability to fix atmospheric nitrogen into a form that can be easily used by plants, such as ammonia or nitrates. This process is critical for soil fertility and the growth of plants, as nitrogen is an essential component of DNA, proteins, and chlorophyll. While Azotobacter and Bacillus are free-living nitrogen fixers, Clostridium and Rhizobium form a symbiotic relationship with plants, with Rhizobium commonly associated with legume plants. Nitrogen-fixing bacteria play a crucial role in maintaining soil health and agricultural productivity.