Nitrogen Fixation in Sugarcane and Pseudomonas Stutzeri with Host Rice

Seventeen bacterial strains were isolated from rhizosphere soil and surface-sterilized roots of sugarcane and were found to represent 12 species distributed in the 6 genera Klebsiella, Burkholderia, Erwinia, Enterobacter, Bacillus, and Ralstonia based on 16S rDNA sequences. A number of oxidation of substrate utilization patterns were observed in the Rifr mutants of P. stutzeri that utilization of carboxylic acids and amino acids significantly increased in several Rifr mutants than that of wild type. To investigate the plant-microbe interaction mechanism, a set of 20 genes responsible for chemotactic motility and root surface colonization was selected and their expression was determined in the presence of rice root exudates. After induction of 1h, it was found that pilK, metE and rpoN transcription increased 5.7, 6.4, and 3.4-fold, respectively, whereas in the fdhE gene has no expression. Consequently, after inductions of 4h, the pilK, fdhE, metE, and rpoN genes were decreased -1.9, -4.4, -0.2 and -0.8-fold, respectively. These results suggest that plant-microbe interaction is controlled by complex regulatory systems.