Synthetic Metabolic Solutions for Enhanced Agricultural Production with Cyanobacteria

The global population continues to increase and food self-sustainability is still an issue for many. Synthetic biology can contribute towards enhancing our food self-sustainability and simultaneously minimizing the impact of the agricultural industry on planetary resources. Two such strategies can reduce our reliance on fossil fuels and enhance productivity. In the first case we are constructing synthetic metabolic solutions that lower the resource demand (in this case N fertilizer), and in the second case the aim is to directly enhance the photosynthetic yield by minimizing the negative impact of photorespiration. In both cases, cyanobacteria acts as the provider, with the intention to either supply nutrients to crop plants, or directly provide feed and food. Taking a systems metabolic engineering approach, our first goal was to enhance our understanding of a model nitrogen fixing cyanobacteria, by constructing a highly curated two-cell model of Anabaena sp. PCC 7120. Optimum solutions for metabolic exchange between heterocysts and vegetative cells were found to exceed the exchange hypothesized from wet-lab experiments. Strains with modified N-metabolism were thereafter used to construct model synthetic consortia and evaluated under varying conditions. The N-metabolism of an amt mutant of Anabaena 7120 responded differently to other model N organisms (e.g. Rhodobacter capsulatus) in terms of NH₃-excretion, but displayed a similar conditional capability to rescue non N-fixing strains as reported previously for Azotobacter vinelandii. In order to implement entirely synthetic pathways that allow for enhanced photosynthetic yield, we are developing more robust engineering methods and studying the conditional importance of the three different photorespiration routes in Synechocystis spp. PCC 6803.