Endophytic nitrogen-fixing Klebsiella variicola strain DX120E promotes sugarcane growth
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Klebsiella variicola bacteria are found in association with plants. Little is known about their colonization patterns, roles, and mechanisms during association with the plant hosts. Here, we identified a nitrogen-fixing bacterium, DX120E, which was isolated from surface-sterilized roots of the ROC22 sugarcane cultivar, as K. variicola by phylogenetic analyses of its 16S rRNA gene, RNA polymerase β-subunit gene, and DNA gyrase subunit A gene sequences. gfp-tagged DX120E was found to colonize at the roots and aerial parts of micropropagated sugarcane plantlets by fluorescence microscopy and confocal microscopy. DX120E was able to survive in soils and colonize in root epidermal cells, intercellular spaces in root cortices, and leaf mesophyll and vascular tissues. DX120E preferentially colonized at root maturation and elongation zones and entered roots via cracks at the emergence site of lateral roots and at disrupted epidermis. DX120E may penetrate root epidermal cells with the aid of their cellulose-degrading enzymes. 15N isotope dilution assay demonstrated that DX120E was able to fix N2 in association with ROC22 sugarcane plants under gnotobiotic condition. DX120E was also able to promote GT21 cultivar growth and plant uptake of N, P, and K under greenhouse condition. Together, this study for the first time shows that a K. variicola strain is able to colonize in its sugarcane plant hosts, to fix N2 in association with plants, and to promote plant growth.
KeywordsColonization Endophytic bacteria Klebsiella variicola Nitrogen fixation Plant growth-promoting bacteria Sugarcane
We thank Dr. Duli Zhao for reviewing the manuscript. This study was supported by the National Natural Science Foundation of China (31171504 and 31101122), Natural Science Foundation of Guangxi Provence (2011GXNSFF018002 and 2011GXNSFA018076), Guangxi Key Laboratory of Sugarcane Genetic Improvement (13-A-03-07), Guangxi Key Laboratory Construction Program (13-051-29), and Science and Technology Development Foundation of Guangxi Academy of Agricultural Sciences (2011YT01 and 2012YZ09).
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