Control of gene expression in rhizosphere bacteria by plant metabolites

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With a growing human population expected to reach over 11 billion by 2100, it is vital that agriculture is able to grow correspondingly to sustain this population size. To date, increases in agricultural yield have been supported by reliance on synthetic fertilisers containing nitrogen produced by the HaberBosch process. However, this is neither environmentally nor economically sustainable. In the natural world, biological nitrogen fixation (BNF) is carried out by prokaryotes using the enzyme nitrogenase. A limited group of plants is able to form symbiotic associations with these prokaryotes, allowing them to benefit from BNF. The most well-studied example of this is the symbiosis between legumes and rhizobia. However, staple cereal crops such as wheat are unable to form a similar symbiosis, meaning that these crops are primarily dependent on Haber-Bosch nitrogen. An ongoing challenge in biological research in the 21st century is that of applying BNF to staple cereal crops. This project aims to extend BNF to cereals by linking nitrogen fixation and excretion in plant growth-promoting rhizobacteria (PGPRs) to a natural plant signal. Bacterial regulatory systems that respond to cereal root exudates will be identified using RNA sequencing, qRT-PCR and lux promoter fusions, and these root exudates characterised using mass spectrometry. Control circuits will be engineered to link these regulatory systems to genes encoding products involved in nitrogen fixation; in particular, the regulatory gene nifA. This will result in the formation of engineered bacterial strains that fix and excrete nitrogen in cereal rhizospheres.