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Analysis of quorum-quenching factor(s) of bacterial isolates selected from potato rhizosphere


Virulence of the plant pathogenic bacteria Erwinia carotovora subsp. carotovora (Ecc) depends on the production and secretion of the extracellular plant cell-wall degrading enzymes, which synthesis is controlled by a complex regulatory system. N-acyl homos erine lactones (HSLs) are involved in induction of the cell wall degrading enzymes synthesis. The HSLs are common signaling molecule of Gram-negative bacteria and play an important role in cell to cell communication between bacterial cell as well as in the interaction between bacteria and higher organisms. Synthesis of HSLs is dependent on the population density and a phenomenon known as "quorum-sensing". Soil bacteria have been identified to be able to degrade HSLs and thus interfere with quorum-sensing. S o far two enzymatic activities have been characterised: an acyl-HSL-lactonase from Bacillus sp. and Agrobacterium tumefaciens and an HSL-acylase from Variovorax paradoxus. Potentially, these enzymes offer a new tool to interfere with virulence factors of ( plant) pathogenic bacteria, which synthesis is regulated by HSLs. The aim of this project will be to characterise an HSL degrading factor produced by bacterial soil species never described before (Ochrobactrum sp. or Delftia). In the initial studies the so il isolates were tested for their capacity to degrade HSL and to inhibit Ecc pathogenicity. One of the pre-selected isolates will be selected for further analysis. Genes involved in HSL-degradation/inactivation will be cloned, and the putative protein will be expressed and purified. Transposon mutagenesis or a cosmid library of a genomic DNA of selected isolate will be used as the potential strategies for a characterisation of the gene encoding HSL-degrading enzyme. The DNA sequence of the putative gene wil l be analysed and the potential protein will be purified. The effect of HSL-degradation of the purified protein will be tested. For that, a Green Fluorescence Protein #

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ul. Bazynskiego 1a

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