Isolation and Genetic Enhancement of Nitrogen-Fixing Rhizobacteria for Promoting Growth in Maize

(Background) Aiming to reduce synthetic fertilizer dependence and enhance soil fertility, this study isolated and characterized nitrogen-fixing bacteria from the maize rhizosphere. (Methods) Nitrogen-free selective media were used for bacterial isolation, followed by detection of the nifH gene and nitrogenase activity. Phylogenetic identification was conducted via 16S rRNA sequencing. Growth-promoting traits, stress tolerance, and pot-based plant inoculation effects were assessed. Genetic modification of strain GN8811 was performed to improve nitrogen fixation and growth promotion. (Results) Seven isolates that carried the nifH gene and exhibited nitrogenase activity were closely related to four genera. Several isolates showed phosphate solubilization, iron chelation, IAA production, or potassium solubilization, with GN2003 and GN8811 tolerating high salinity and variable pH. Inoculation with GN8811 promoted maize growth comparable to nitrogen fertilization, and its genetically modified derivative (ΔnifL::PrpoD) showed further improvement even under high nitrogen conditions. (Conclusions) These findings highlight the potential of combining microbial screening with genetic engineering to develop efficient bioinoculants for sustainable maize cultivation.