In the last three years one of the most fundamental changes in our perception of microbial ecosystems, is the recognition that most bacteria have specialised cell to cell diffusible signalling systems (quorum) sensors) that allow them to constantly monitor their cell density. This is achieved by secretion of N-acyl homoserine lactones (AHLs); as these compounds accumulate they are recognized by regulatory proteins that induce (and possibly repress) expression of genes in a cell-density dependent manner. It is now apparent that "cross talk" can occur by bacteria from one genus reacting to AHLs made by bacteria from another genus. These signalling systems appear to be particularly important in soil bacteria, resulting in the induction of genes that influence a range of physiologically diverse processes that are important for pathogenesis, symbiosis, plasmid transfer, enzyme secretion and production of small metabolites (antibiotics etc) important for survival in soils and in the rhizosphere. These processes are all likely to be important with respect to the efficacy of inoculant strains.
Undoubtedly, most (if not all) commercial bacterial inoculants that are currently used (or are being developed) as biofertiliser, biocontrol or bio- remediation agents, utilise AHL based communication systems. However, although those physiological traits crucial for inoculant efficacy are probably controlled by AHL-based signalling, we currently know very little about the role of quorum sensing systems with regard to plant microbe interactions or on the effects on the indigenous micro-flora. The design of inoculant strains must now take cognisance of quorum sensing and there is a need to evaluate this type of communication with regard to inoculant development and environmental impact. The objectives of this proposal are: (a) Characterise the quorum sensing systems used by Pseudomonas and Rhizobium inoculant strains. (b) Identify the genes involved in quorum sensing in these inoculant strains . (c) Synthesise novel quorum sensing molecules to test their role in plant microbe interactions.
(d) Initiate an Analysis of the role of quorum sensing systems in general performance in-vitro and in efficacy of biofertilisers and biocontrol bacteria using mutants defective in production and/or perception.
(e) Assess the potential for: inoculant improvement; alterations in viability (both in shelf life and soil survival) and effects of inoculants on plasmid transfer in soil and on pathogenicity of specific indigenous soil plant pathogens.
Funding SchemeCSC - Cost-sharing contracts
91190 Gif Sur Yvette
2333 AL Leiden
HP2 7SU Hemel Hempstead