THE FIXATION OF NITROGEN BY BACTERIUM AEROGENES AND RELATED SPECIES

Abstract

Of 23 strains of Bact. aerogenes isolated from soil, flour and water, 2, possibly 3, strains were found which fixed atmospheric N when grown in routine N-free media. Not all strains of Bact. radio-bader were found to fix N. Bact. aerogenes or Bact. radiobader, often both, were always encountered in isolation of Azotobader, and Bact. radiobader was found nearly always in isolation of nodule bacteria. Bact. cloacae was more often found in soil than Bact. aerogenes; no strains were found to fix N. Bact. radici-cola is very closely related phylogenetically to Bact. radiobader and Bact. aerogenes. The placing of the genus Rhizobium by Bergey among the autotrophic bacteria (family Nitrobacteriaceae) has no scientific justification. If maintained as a genus it belongs in or near the colon-typhoid group. Need for further work on Bact. radiobader is indicated.