Endophytic Colonization Of Rice By Plant Growth-Promoting Bacterium Klebsiella Oxytoca Strain HMLR8 And Roseateles Depolymerans Strain HMLR13

35 endophytic diazotrophic bacteria from surface-sterilized roots and stems of Echinochloa crusgalli which grows luxuriantly with no additional nitrogen fertilizer were isolated. Of all these bacteria, two isolates HMLR8 and HMLR13 showed the ability of infecting rice variety ZH-11 seedlings and growth-promoting property. These isolates were identified as Klebsiella oxytoca strain HMLR8 and Roseateles depolymerans strain HMLR13 respectively on the basis of 16S rDNA sequence and biochemical tests analysis. Amplification of nifH by polymerase chain reaction (PCR) and detection of nitrogenase activity by acetylene reduction assay confirmed the diazotrophic nature of HMLR8 and HMLR13. As an endophytic diazotrophic bacterium never been reported, HMLR13 was tagged with gfp gene and the resulting conjugant was inoculated to endophyte-free rice seedlings to detect its colonization and distribution in the tissues of rice seedlings. The results demonstrated that:(1) incubation of these two isolates especially HMLR8 resulted in significant increase in root/shoot length and nitrogen content of rice seedlings; (2) Roseateles depolymerans strain HMLR13 was a new endophytic diazotrophic bacterium which displays maximum nitrogenase activity of 406.5593 nmol C2H4ml-1h-1 when using glycerine as single carbon source.