1. Aguilar O M and Favelukes G 1982 Requirement for carbon dioxide for nonsymbiotic expression of Rhizobium japonicum nitrogenase activity. J. Bacteriol. 152, 510–513.
2. Akkermans A D L 1971 Nitrogen fixation and nodulation of Alnus and Hippophaë under natural conditions. Ph.D. Thesis, University of Leiden, The Netherlands.
3. Akkermans A D L, Roelofsen W, Blom J, Huss-Danell K and R Harkink 1983 Utilization of carbon and nitrogen compounds by Frankia in synthetic media and in root nodules of Alnus glutinosa, Hippophaë rhamnoides and Datisca cannabina. Can. J. Bot., 2793–2800.
4. Arias J M, Fernandez-Vivas A, Montoya E 1983 Evidence for an activating substance related to autolysis in Myxococcus coralloides D. Arch. Microbiol. 134, 164–166.
5. Baker D, Torrey J G and Kidd G H 1979 Isolation by sucrose-density fractionation and cultivation in vitro of actinomycetes from nitrogen-fixing root nodules. Nature London 281, 76–78.