Harnessing biological nitrogen fixation: Multi-scale engineering for self-sustaining agroecosystems

Certain prokaryotic microorganisms possess the extraordinary ability to convert atmospheric nitrogen gas into ammonia in a process known as biological nitrogen fixation. Harnessing this process as a substitute for chemical nitrogen fertilizers offers substantial benefits for agricultural productivity. Improving the efficiency of nitrogen fixation and enabling crops to fix nitrogen biologically are crucial research goals. This review explores molecular mechanisms governing nitrogenase activity, engineering strategies for enhancing nitrogen fixation efficiency in non-diazotrophic hosts, and evaluates synthetic biology approaches for establishing robust nitrogen-fixing systems. We emphasize the integration of multi-scale engineering - from nitrogen fixation circuit design in microbial chassis to rhizosphere microbiome reprogramming to engineered nitrogen-fixing crops and field applications at the ecosystem level - as critical pathways toward creating self-sustaining agroecosystems. We conclude by discussing key challenges and identifying research priorities to expand the practical applications of biological nitrogen fixation. This review provides a framework for developing multi-layered bioengineering solutions that enhance crop productivity while reducing ecological impacts, ultimately advancing the realization of self-regulating agricultural ecosystems.