Abstract
Aims To study nitrogen contribution to cucumber derived from nitrogen fixation of Paenibacillus polymyxa WLY78.Methods The nif gene cluster deletion mutant (ΔnifB-V) of P. polymyxa WLY78 is constructed by a homologous recombination method. The GFP-labeled ΔnifB-V mutant was used to inoculate cucumber and to study colonization by confocal laser scanning microscope. The effects of plant-growth promotion were investigated by greenhouse experiments. The nitrogen fixation contribution was estimated by 15N isotope dilution experiments. Results Deletion of nif gene cluster of P. polymyxa WLY78 resulted in complete loss of nitrogenase activity. Observation by laser confocal microscopy revealed ΔnifB-V mutant can effectively colonize cucumber root, stem and leaf tissues, like wild-type P. polymyxa WLY78. Greenhouse experiments showed that inoculation with P. polymyxa WLY78 can significantly enhance the lengths and dry weights of cucumber roots and shoots, but inoculation with ΔnifB-V mutant can not. 15N isotope dilution experiments showed that cucumber plants derive 25.93% nitrogen from nitrogen fixation performed by P. polymyxa WLY78, but the ΔnifB-V mutant nearly can not provide nitrogen for plant growth. Conclusions This present study demonstrates that nitrogen fixation performed by P. polymyxa WLY78 is responsible for cucumber growth promotion.
Nitrogen Fixation by Paenibacillus Polymyxa WLY78 is Responsible for Cucumber Growth Promotion
