Agrobacterium tumefaciens Is a Diazotrophic Bacterium

摘要

This is the first report that Agrobacterium tumefaciens can fix nitrogen in a free-living condition as shown by its abilities to grow on nitrogen-free medium, reduce acetylene to ethylene, and incorporate ¹⁵N supplied as ¹⁵N2. As with most other well-characterized diazotrophic bacteria, the presence of NH4⁺ in the medium and aerobic conditions repress nitrogen fixation by A. tumefaciens. The system requires molybdenum. No evidence for nodulation was found with pea, peanut, or soybean plants. Further understanding of the nitrogen-fixing ability of this bacterium, which has always been considered a pathogen, should cast new light on the evolution of a pathogenic versus symbiotic relationship.