Centre for Rhizobium Studies - image

Research activities

The major research activities of the CRS can be broadly summarised within the following themes :

1. Optimising nitrogen fixing symbiotic interactions to improve legume productivity

This research area has a focus on understanding the current challenges for optimizing nitrogen-fixing symbiotic interactions to improve legume productivity in agriculture. For maximum productivity the inoculum strain-legume host partnership needs to fix high amounts of N, and this requires the bacteria to infect roots and develop in the nodule into nitrogen-fixing bacteroids. A key question this research addresses is “what are the biological mechanisms determining a compatible (high nitrogen-fixing) rhizobia strain-legume host combination?” We know there are many strains of rhizobia that can nodulate a particular legume, but only relatively few can fix a high amount of N. Current inoculants strains used in agriculture have been selected by a long and time-consuming ‘trial and error’ process. Understanding the biology of nitrogen fixation compatibility will lead to more efficient targeted screening protocols, yielding improved inoculant strains that fix high amounts of N across diverse target host legumes.

2. Physiology and molecular biology of the root nodule bacteria

Not only are the RNB capable of forming nitrogen-fixing symbiotic interactions with legumes, but they are also successful free-living soil inhabitants. Studying the physiology and molecular biology of these organisms is therefore a crucial component of understanding how these organisms survive and thrive in these two very different ecological niches. Specifically, research at the CRS in this area seeks to unravel the molecular mechanisms by which RNB survive soil stresses such as low pH; how they completely change their way of life and cellular machinery to ultimately be converted into nitrogen-fixing ‘factories’ for the plant’s benefit; what is the genetic basis for highly effective and highly competitive RNBs.

3. Domesticating new legumes for agriculture

Because of the critical role symbiosis has in legume adaptation, the CRS has been active in developing and domesticating new legumes for agriculture, particularly for acid and sandy soils. Through the CRS, Murdoch University is a 50% owner with DAFWA of the new early flowering serradella cv Eliza. With funding from ACIAR, and assistance from collaborators in South Africa, CRS has been domesticating suffrutescent perennial legumes collected from the fynbos the Western Cape. Lebeckia is the most advanced example of this.

4. Genomics of root nodule bacteria

The CRS genome sequencing program aims to establish the genomes of a diverse range of root nodule bacteria (RNB) encompassing both commercial and non-commercial strains. Strains already completely sequenced include Sinorhizobium medicae WSM419, strains of the clover nodulating Rhizobium leguminosarum bv. trifolii and 3 strains of Mesorhizobium spp. The genomes of an additional 20 strains including 11 Rhizobium leguminosarum bv trifolii strains, 3 Rhizobium leguminosarum bv viciae strains, 4 Lupin nodulating strains and 2 Microvirga strains are emerging from the sequencing pipeline. An international consortium of scientists from the CRS, the US Department of Energy’s Joint Genome Institute and members of the international RNB and nitrogen fixation community are also working to establish the genomes of 100 RNB isolates in the Genomic Encyclopedia for Bacteria and Archaea-Root Nodule Bacteria (GEBA-RNB) project. The sequencing of so many RNB genomes represents a huge investment in nitrogen fixation research and will provide a scaffold for future genetic studies.

5. Australian native legume symbioses

Australia boasts a large array of native legume species. However, there is currently very little information available detailing the relationships between these native legumes and their RNB symbionts, particularly in Western Australia. The CRS has conducted several studies to better understand the microbial diversity of native legume-nodulating bacteria. One approach has been to identify RNB with the potential for agricultural applications as inoculants on existing legume crops. Another is assessing the use of indigenous RNB with provenance legumes to rehabilitate long term degraded sites in dryland areas. Members of the CRS have also studied the diversity of RNB populations on the legumes of the South-West of WA.

6. MINTOPE: Overcoming challenges in transition from mining to agriculture