Which organisms are referred to as "biological nitrogen fixers"?

The term "biological nitrogen fixers" refers to microorganisms such as bacteria, archaea, and certain types of cyanobacteria that are capable of converting atmospheric nitrogen gas into a form that can be used by plants and other organisms. These microbes play a vital role in the nitrogen cycle, which is the process by which nitrogen is converted into different forms and cycled through the environment. Lichens are not typically involved in nitrogen fixation, although they can absorb nitrogen from the atmosphere in small quantities. Animals and fungi also do not play a direct role in nitrogen fixation, although they can indirectly benefit from the nitrogen that is made available through this process.