Anaerobic Nitrogen-Fixing Consortia Consisting of Clostridia Isolated from Gramineous Plants

We report here the existence of anaerobic nitrogen-fixing consortia (ANFICOs) consisting of N 2 -fixing clostridia and diverse nondiazotrophic bacteria in nonleguminous plants; we found these ANFICOs while attempting to overcome a problem with culturing nitrogen-fixing microbes from various gramineous plants. A major feature of ANFICOs is that N 2 fixation by the anaerobic clostridia is supported by the elimination of oxygen by the accompanying bacteria in the culture. In a few ANFICOs, nondiazotrophic bacteria specifically induced nitrogen fixation of the clostridia in culture. ANFICOs are widespread in wild rice species and pioneer plants, which are able to grow in unfavorable locations. These results indicate that clostridia are naturally occurring endophytes in gramineous plants and that clostridial N 2 fixation arises in association with nondiazotrophic endophytes.