Fixation of Dinitrogen by Free-Living Microorganisms

Abstract

The purpose of this article is not to review exhaustively all that is known about nitrogen-fixing microbes but to provide a reasonable coverage of more recent discoveries in the field. It is primarily concerned with the microbiology of the free-living nitrogen-fixing organisms, although casual reference to symbiotic systems has been made. With this in mind, I shall attempt not to burden the reader with microbiological minutiae but will restrict coverage to those biological aspects which help us understand how such a diverse assortment of microbes can grow with N2 gas as their sole nitrogen source. The discovery of the nitrogen-fixing character in a certain microorganism sometimes necessitates a reevaluation of its taxonomic position. Where necessary, this has been done.