The 'oxygen paradox' of dinitrogen-fixing bacteria

N-2 fixation by aerobic bacteria is a very energy demanding process, requiring efficient oxidative phosphorylation, while O-2 is toxic for the nitrogenase complex. N-2-fixing bacteria have evolved a variety of strategies to cope with this apparent "O-2 paradox". This review compares strategies that azospirilla and other well-known N-2-fixing soil bacteria use to overcome this O-2 paradox. Attention will be given to the relationships between the natural habitat of these soil bacteria and their prevailing adaptations. In view of this knowledge the following questions will be addressed: are the specific adaptations observed in azospirilla sufficient to allow optimal proliferation and N-2 fixation in their natural habitat? Could improving the O-2 tolerance of the N-2-fixing process contribute to the development of more efficient strains for the inoculation of plants