Physiology, biochemistry, and genetics ofazospirillumand other root‐associated nitrogen‐fixing bacteria

The advent of the acetylene reduction assay for determination of nitrogenase activity in the mid‐1960s had a great impact on the development of nitrogen‐fixation research, as a whole, and of plant‐diazotrophic bacteria associations, in particular. The number of diazotrophic rhizocoenosis increases continuously. Azospirilla, Azotobacteraceae, Enterobacteriaceae, Pseudomonadaceae, Bacillaceae, and other diazotrophs have been found closely associated with plant roots and could contribute substantial amounts of fixed nitrogen to the associated plant. Additionally, these bacteria may benefit the plant through the production of growth substances. In this article, the relevant literature on physiology, biochemistry, and genetics of these diazotrophs is reviewed. An integrated knowledge of these disciplines is essential for carrying out suitable manipulation of the environment and of the rhizocoenotic diazotroph for crop improvement.