iCASE Studentship with Legume Technology: Understanding bacterial colonisation of legume roots and nodules

Colonisation by bacteria of the zone surrounding plant roots (rhizosphere) is crucial to plant productivity. In spite of its importance rhizosphere colonization is poorly understood but recent advances in genome sequencing and analysis makes it possible to address this complex topic in exciting new ways. Global food security depends on sustainably maximising crop yield whilst decreasing use of costly fertilizers, which cause release of the potent greenhouse gas N2O from soils. The largest input of fixed nitrogen in the biosphere comes from the biological reduction of atmospheric N2 to ammonium, mainly through Rhizobium–legume symbioses, within which bacteria reduce N2 to ammonia for supply to the host. This frees many of the world’s major crops (e.g. soybeans, alfalfa, and peas) from nitrogenous fertilizer application and transferring nodulation to non-legume crops is a long term goal almost certain to trigger a second, environmentally sustainable, green-revolution. However, only the bacterial symbiont fixes N2 so for successful transfer we must also understand how rhizobia grow in the rhizosphere of plants and colonize their roots. We have developed radically new methods to image bacteria in their interaction with roots both temporally and quantitatively using lux fusions. This allows us to genetically dissect the bacterial and plant pathways needed for attachment, colonisation and for nodulation of legume hosts by rhizobia.

One of the biggest problems in the use of legumes is that the most efficient bacteria at fixing nitrogen (i.e. effective bacteria) are often not the most competitive (i.e. infective) at colonising and nodulating the plant. We have begun developing methods to analyse the competitiveness and effectiveness of rhizobia in highly parallel screens using nifH::lux and nifH:celB/gusA detection of bar coded bacteria. In this project this will be adapted to a wide range of rhizobia, including pea, phaselous bean and soybean infecting rhizobia. This will require extensive genetic manipulation of the detection systems, including its engineering into a Tn7 integration system for soybean infecting rhizobia. A wide scale screen for competitive bacteria in 2-3 crops plants will then be undertaken using field isolated bacteria. Finally, in the specific case of pea the genetic determinants of the most competitive bacteria will be assessed by an InSeq screen using the mariner transposon specifically adapted for use in rhizobia. This will allow the student to move from the highly applied to fundamental aspects of bacterial physiology and genetics. The project will be conducted in the Department of Plant Sciences at Oxford with a 3 month rotation at Legume Technology in Nottingham.

This project is supported through the Oxford Interdisciplinary Bioscience Doctoral Training Partnership (DTP) BBSRC Industrial CASE (iCASE) studentship programme. The student recruited to this project will join a cohort of students enrolled in the DTP’s interdisciplinary training programme, and will be able to take full advantage of the training and networking opportunities available through the DTP. For further details please visit www.biodtp.ox.ac.uk.

Prospective applicants should contact the project supervisor Professor Philip Poole ([Email Address Removed]) prior to submitting an application.

Applications for this project will be made via the Oxford Interdisciplinary Bioscience DTP. For further details please visit www.biodtp.ox.ac.uk.

Attributes of suitable applicants:

A background in bacterial or plant sciences or molecular biology or biochemistry would be suitable.