Engineering Rhizobacteria for Biological Nitrogen Fixation in Cereals

An increasing global population puts a greater burden on food productivity and security. New
crop varieties are being bred for greater yield and pest resistance, however they still require
fertilisation to supply nitrogen which is normally limited in the soil. Nitrogen fixing bacteria in
the soil provide an opportunity to reduce the dependency of agriculture on in-organic fertiliser
produced by industry, which pollute ground water and release the potent greenhouse gas N2O.
However, biological nitrogen fixation is currently mainly limited to legumes which require
complex two-way signalling and physiological changes to establish symbiosis with nitrogen fixing
rhizobia. The traits required for colonisation by rhizobia are poorly understood and therefore
difficult to extend to cereal crops. Our aim is to use cereal endophytes, such as the versatile
nitrogen fixer Azorhizobium caulinodans, as a chassis to engineer and enhance biological
nitrogen fixation and ammonia release to the host in cereals. A synthetic orthogonal transkingdom signal will be used to establish a plant-microbe interaction between cereals and
rhizobacteria and control nitrogen fixation and other plant growth promoting traits in
engineered microbes.