Species of Rhizobium bacteria form a symbiosis with legume roots where they fix atmospheric nitrogen and provide this to the host plant. Many rhizobia also utilise nitrate/nitrite and must carefully regulate this pathway to control nitric oxide formation, which inactivates nitrogenase. The legume-Rhizobium symbiosis has significant benefits for agricultural sustainability by decreasing the need for synthetic nitrogen fertilisers and associated environmental pollution. Furthermore, legume breakdown returns nitrogen to the surrounding soil and acts as a green fertiliser to enhance soil health.
Surprisingly little is known about the molecular mechanisms of rhizobial growth, its link to nitrogen utilisation and plant colonisation via infection thread structures. Bacterial growth can take place either at lateral or polar locations driven by cytoskeletal proteins. Rhizobiales species exhibit polar growth but very little is understood of the cytoskeletal network that controls this growth in these bacteria. Polar cytoskeletal complexes have been extensively studied in a different group of bacteria, the actinomycetes, where cytoskeletal complexes are not only essential for polar growth but also for cellular organisation of proteins with wide ranging functions.
This work will identify the molecular basis for polar growth amongst the Rhizobiales and determine how the rhizobial cytoskeleton controls the cellular localisation of enzymes for N-fixation and N-cycling. With our industrial partner (PGRO), we will study the sequence divergence of both cytoskeletal and N-cycling proteins by analysing field samples from selected UK locations. Overall, this work will shed new light on how the bacterial cytoskeleton affects the legume-Rhizobium symbiosis and regulates symbiotic nitrogen-fixation in agricultural contexts.