Modern agriculture relies on the copious application of synthetic nitrogen (N) fertilisers. These fertilisers are produced using vast amounts of fossil fuels and their use is associated with several environmentally deleterious effects, such as the eutrophication of water bodies and volatilisation as greenhouse gases. Thus, alternative, environmentally friendly strategies are needed to deliver N to crops. Root associated, N fixing bacteria have long been researched as an avenue to improve agricultural sustainability as a kind of plant probiotic. However, these have not been successfully implemented in a meaningful way and do not persist in the inherently competitive rhizosphere environment. Rather than studying these bacteria in isolation with their plant host, new evidence suggests that crop inoculants should be designed with regard to the entire root microbiome and its ecology. These novel inoculants are made up of multiple bacteria strains to make up synthetic communities (SynComs). Studies of root microbiomes largely conclude that a core group of bacteria consistently colonise specific plant species roots regardless of changes in environment, genotype or the starting soil bacteria population. While these core bacteria do not usually directly aid in reducing the effect of N starvation, they are being increasingly implicated as important regulators of microbiome structure. Additionally, they have been shown to improve the N fixation rate of SynComs and may also aid in root colonisation and longer-term persistence in the field.
The aim of this project is to develop a root associated SynCom for the model monocot Brachypodium distachyon to alleviate the effects of N starvation. The core root microbiome of B. distachyon will be defined from plants grown in a variety of soils. Concurrently, bacteria will be isolated from the roots of B. distachyon and screened for N fixation and plant hormone production. Currently, 141 isolates have been found. Using information about the root community taxonomy, isolates will be selected to make up SynComs containing N fixers and bacteria representative of the core B. distachyon root microbiome. N fixation rate of N fixers in isolation and as members of SynComs will be quantitively measured to determine whether non N fixing members of the core B. distachyon root microbiome increase N fixation in culture. Finally, the ability of SynComs and N fixers in isolation to promote the growth of B. distachyon under N limiting conditions will be assessed.