Towards Design of Endophytic Bacteria That Can Deliver Fixed Nitrogen to Cereal Crops

Most cereal crops require a significant amount of nitrogen fertilizer to reach their yield potential. Acquiring nitrogen fertilizers is difficult for poor farmers in developing countries. In contrast, the excessive use of nitrogen fertilizers in developed countries leads to significant environmental and sustainability problems. Unfortunately, unlike legumes, most cereals cannot obtain a significant amount of nitrogen through biological nitrogen fixation. Low oxygen levels (micro-aerobic conditions) and carbon availability are two prerequisites for efficient biological nitrogen fixation with most aerobic bacteria. We hypothesized that these two features may be more available deep inside of root tissues than on their surface. Bacterial endophytes can colonize plant tissues internally without eliciting significant host defense responses. These endophytic bacteria enter root tissues through cracks caused by lateral root formation or wounds. Thus, we are aimed at designing endophytic bacteria residing in cereal roots such that they are capable of fixing nitrogen efficiently and providing nitrogen to the plant. Preliminary evidence shows the activity of nitrogenase after the colonization of maize with some engineered endophytic bacteria. The control of nitrogen fixation is therefore ready to be placed under synthetic control, for example, of plant-derived signals in chassis organisms.