The spermosphere model. I. Its use in growing, counting, and isolating N2-fixing bacteria from the rhizosphere of rice

The composition of the N2-fixing microflora of a rice rhizosphere was studied by a new enrichment and isolation procedure: rather than using an artificial C source, the exudates from a germinating seed ("the spermosphere model") are used. In this study, this system gave N2-fixing isolates with a frequency of 65%. Thirty-two of the many isolates obtained have been studied in detail; these were Klebsiella oxytoca, Enterobacter cloacae, Pseudomonas paucimobilis, and Azospirillum. All these bacteria were present at densities higher than 105 per gram of dry soil in the intial rice rhizosphere.

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