1. Adams, T.H. and Chelm, B.K. (1988) J. Gen. Microbiol. 134, 611–618.
2. Alloway, D., Voesten, B. and O’Gara (1995) FEMS Microbiol. Lett. 128, 241–245.
3. Amar, M., Patriarca, E. J., Manco, G. and Bernard, P. (1994) Mol. Microbiol. 11, 685–693.
4. Appleby, C.A. (1974) in The biology of nitrogen fixation (Quispel, A. ed.), pp. 521–554, North Holland/Amer.Elsevier, Amsterdam/New York.
5. Appleby, C.A. (1984) Annu. Rev. Plant Physiol. 35, 443–478.