Characters identification and sugarcane growth promotion analysis of an endophytic nitrogen fixing bacteria GXS16

Abstract:

[Background] The nitrogen fertilizer input for sugarcane crop production is very high in China, which result in the high planting costs and cause the field pollution. Sugarcane can obtain high levels of nitrogen via N₂-fixation by associated N₂-fixing bacteria. It is imperative to substantially reduce the nitrogen fertilizer inputs and to substitute nitrogen fertilizers with biological nitrogen fixation to develop a high benefit-cost ratio and environmentally benign sugarcane production in China. [Objective] The aim of this study was to systematically identify efficient endophytic nitrogen fixing bacteria of sugarcane, as well as demonstrate their potential for associative nitrogen fixation and plant growth promotion ability. [Methods] An endophytic diazotroph strain GXS16 was isolated from the roots of sugarcane, and its nitrogen fixation ability was tested by acetylene reduction assay and nifH gene sequence amplification. Strain GXS16 species classification was identified by its culture and the microscopic observation characters, Biolog detection and 16S rRNA gene sequence analysis together. Strain GXS16 was inoculated with micro propagated sugarcane seedlings to detect its growth promotion ability and associative nitrogen fixation activity with ¹⁵N isotope dilution method. [Results] Strain GXS16 showed a high acetylene reduction activity of 2.42 µmol-C₂H₄/(h·mL). Based on phenotypic characteristics, Biolog system test, 16S rRNA gene, nifH and acdS gene sequence analysis, GXS16 was classified into Burkholderia sp. Furthermore, GXS16 containing ACC deaminase activity, and other plant growth promoting traits as IAA production and phosphate solubilization ability. GXS16 significantly promoted the growth of sugarcane seedlings. Compared with the uninoculated controls, GXS16 increased plant height and dry weights more than 15% and 20%, respectively. ¹⁵N isotope dilution assays demonstrated that the associative nitrogen fixation rates of GXS16 in the sugarcane roots, stems and leaves were 7.69%, 15.64% and 8.72%, respectively, which were higher than that of model strain G. diazotrophicus PAL5. [Conclusion] Strain GXS16 has a great potential to efficiently fix N₂ in sugarcane and promote sugarcane growth.