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Biological inoculants for seed/plant establishment

Exploitable results

Most nicroorganisms require iron at micromolar concentrations for growth. Bacteria and fungi have therefore evolved high-affinity iron uptake systems to import iron into the cell. Such siderophore-mediated iron assimilation is an important physiological trait required for the survival of microbes in a diverse range of environments. Furthermore, fluorescent siderophores produced by fluorescent pseudomonad strains have been implicated in the biological control of pathogenic fungi and the suppression of plant disease. The objectives of this project involved the integrated assessment of fluorescent Pseudomonas strain M114 with regard to its biological control ability and the elucidation of the mechanisms mediating its production of a fluorescent siderophore. In summary, a gene (pbsC) encoding the biosynthesis of the fluorescent Pseudomonas M114 siderophore was successfully identified and cloned. In the environment, iron-free siderophores are released from bacterial cells where they bind to ferric iron, forming a ferric-siderophore complex. This complex is then transported into the cell. In this project, the gene (pbuA) responsible for the synthesis of an iron uptake protein involved in this process was also cloned from strain M114. In addition, further analysis of the complex regulation of siderophore production, and the production of other extracellular factors, by strain M114 resulted in the identification of pbrA which is an alternative sigma factor and a member of the ECF family of sigma factors. Understanding the mechanisms involved in key physiological traits such as iron assimilation and the production of extracellular compounds may have considerable implications for the development of effective microbial inoculants with potential applications in the areas of biological control of crop pests and bioremediation. In addition, these recent observations may prove significant in providing us with a clearer understanding of the interactions that occur between infecting microorganisms and their environments. An example of such an interaction may be that which occurs between the cystic fibrosis lung and the pathogenic strain of Pseudomonas aeruginosa.