Breaking the Salinity-Nitrogen Fixation Trade-Off: Engineering A Synthetic Nitrogen-Fixing Vibrio natriegens Strain

SUMMARY Inefficient nitrogen fixation in legumes under saline stress threatens food security, while conventional symbiotic nitrogen fixation is limited by host specificity and saline stress inhibition. This study engineered Vibrio natriegens with nitrogen fixation genes, creating a saline-tolerant, broad-host-range nitrogen-fixing bacteria that enhances plant-microbe interactions through reprogrammed nitrogen metabolism. We demonstrated that engineered nitrogen-fixing V. natriegen significantly enhanced soybean growth and nodulation under saline stress. It also activated nitrogenase gene ( nifHDK ) expression in rhizosphere bacteria and increased the abundance of rhizosphere diazotrophs. This study presents a novel approach for developing stress-resilient crop-microbe symbioses, offering a sustainable solution to improve crop growth under saline stress.