Isolation and characterization of nitrogen-fixing bacteria from sugarcane rhizosphere.

Abstract

 The seven nitrogen fixing bacterial strains were isolated from rhizosphere soil and surface sterilized roots of sugarcane. The aimed of this study were to isolate nitrogen-fixing bacteria, determine the nitrogen-fixing ability and test the indole acetic acid production. It was found that the five isolated species were distributed in the two genera as Klebsiella and Burkholderia based on 16S rRNA sequence. The PCR amplification of nifH gene showed that seven produced the expected 360-bp amplification product. The molecular identification results from 16S rRNA analyses of these bacteria were also corroborated with the morphological and biochemical data. The nifH gene sequences from the strains belonging to Klebsiella showed that the strains clustered with Klebsiella sp but the nifH gene for Burkholderia was not detected. The ability to fix nitrogen was verified by the acetylene reduction assay and the variation of nitrogenase activities were 1.29±0.4 to 29.63±0.3 nmol C2H4/h/mg protein. The highest nitrogenase activity found in Gp47, the type strain Klebsiella pneumoniae strain sctcc295; was 29.63±0.3 nmol C2H4/h/mg protein. Diazotrophic strains were assessed for plant-growth-promoting trait such as indole acetic acid production. The highest indole acetic acid production was found in Gp10, the type strain Klebsiella sp. strain zmmo which was 99.0±7 µg/ml.