Dinitrogen fixation by obligate and facultative anaerobic bacteria in association with cellulolytic fungi

The anaerobic bacterium Clostridium butyricum is the major contributor to nitrogen gains by a cellulolytic/nitrogen-fixing population isolated from straw. Growth of the anaerobe is supported by the products of fungal cellulases. The facultative anaerobe Enterobacter cloacae does not make a significant direct contribution to nitrogen fixation but in association with C. butyricum allows the anaerobe to grow under "aerobic" conditions. The major function of E. cloacae is thought to be provision of oxygen-depleted microsites.