Enhancing plant nutrition with rhizosphere microbes


Providing sustainable food yields to an ever increasing global population is one of the greatest challenges of this century. New techniques are needed that will provide increased crop growth without damaging the environment. Inoculation of cereal crops with plant growth promoting (PGP) bacteria is such a technique, which provides an increase in plant growth either by stimulating nitrogen fixation, protecting against pathogen attack, or through hormonal effects. Although this technique has great potential, the efficiency of the process is quite variable, partly because interactions between the inoculant bacterium and the specific crop cultivar used may be suboptimal, but also because plant growth may be limited by supply of nutrients other than nitrogen, such as phosphorus and sulphur. Provision of these nutrients for plant nutrition is largely dependent on cycling of organic forms of these elements by the soil microflora. The diversity of the soil microbial community is directly affected both by soil conditions and by plant species, and. understanding the three-way partnership of these organisms has considerable implications for the success of inoculation with beneficial microbes.


Associate Professor Michael Kertesz, Professor Richard Trethowan

Research Location

Sydney Institute of Agriculture - Australian Technology Park

Program Type



In the absence of fertilizers, nitrogen supply to crops is largely dependent on symbiotic and nonsymbiotic N-fixation, but the rhizosphere community also plays an essential role in transformation and mobilization of P and S. The diversity and activity of P and S-mobilizing strains in wheat and legume rhizospheres are affected by plant genotype and N-fixing inoculum. A better understanding of the interactions between plant cultivar, N-fixing bacteria and the organisms responsible for P and S metabolism will allow us to make more accurate predictions for crop management. The proposed Ph.D. project will use cutting edge molecular tools to examine how variations in crop cultivar and inoculant regime affect the dynamics of the rhizosphere community, and the activity and identity of the organisms that catalyse phosphorus and sulfur cycling in agricultural soils. The student will:
Screen crop cultivars (legumes or wheat) for those that respond most strongly to inoculation with nitrogen-fixing organisms, and analyze stability of colonization;

  • Characterize the rhizosphere microbial community structure for these cultivars, using T-RFLP and/or denaturing gel electrophoresis (DGGE) and gene sequencing to assess the impact of colonization by N-fixers;
  • Characterize the impact of increased N-fixation on mobilization of S and P by specific expression analysis of soil bacteria genes known to be involved in these processes;
  • Extend the results obtained in pot experiments to larger field trials, in order to test the hypotheses generated in a more applied environment.

Additional Information

This project would suit a student with an interest in soil microbiology, and some background in molecular genetics. The plant work will be primarily in the glasshouse, under controlled conditions, and some experience with plant cultivation would therefore be useful, though it is not essential. Potential applicants may be interested in reading the following publications:

  • Kennedy, I.R., Choudhury, A. T. M. A. and Kecskés, Mihály. (2004) Nonsymbiotic bacterial diazotrophs in crop-farming systems: Can their potential for plant growth promotion be better exploited? Soil Biology & Biochemistry 36, 1229-1244.
  • Kertesz, M. A., Fellows, E. & Schmalenberger, A. (2007). Rhizobacteria and plant sulfur supply. Adv. Appl. Microbiology 62, 235-268,

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soil, rhizosphere, Nitrogen fixation, plant growth promotion, sulfur, phosphorus, crop, Azospirilllum

Opportunity ID

The opportunity ID for this research opportunity is: 1101

Other opportunities with Associate Professor Michael Kertesz