Some effects of nitrogen-fixing bacteria on the growth of non-leguminous plants

Abstract

During the course of an investigation on “The Cross-inoculation of the nodule-forming bacteria from Leguminous and non-Leguminous plants,”* it was noticed that in all bacterial cultures prepared from the algal zone of the root-tubercles of cycads taken from below the surface of the soil, Pseudomonas radicicola was associated with a species of Azotobacter . In Order to determine to what extent, if any, this association gave an increased power of assimilating free nitrogen, the two forms were obtained as pure cultures by successive platings on a medium composed of maltose 20 grammes, monobasic potassium phosphate 0·5 gramme, sodium chloride 0·5 gramme, calcium carbonate 0·5 gramme, ferrous sulphate 0·1 gramme, agar 15 grammes and distilled water 1000 c. c. Separate cultures of each and a mixed culture were then grown in fluid media in duplicate 500 c. c. Erelenmeyer flasks containing 250 c. c. Of the above medium, omiting the agar but adding 10 grammes of mannite. Control flasks were kept side by side with the inoculated flasks.