Pili mediated DNA exchange in the third domain of life

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Inter- and intra species transfer of DNA plays a vital role in processes like survival under stress conditions, acquiring new traits by horizontal gene transfer and pathogenesis. Different organisms have evolved a variety of mechanisms to transfer DNA to other cells or the environment or take up DNA. The thermoacidophilic archaeon Sulfolobus acidocaldarius possesses a unique pilus system that is induced by treatment with UV light and is subsequently involved in DNA exchange between aggregated Sulfolobus cells. This project will employ biochemical and genetic methods to elucidate the mechanism of pilus assembly, sensing of other Sulfolobus cells and initiation of auto-aggregation. Deletion mutant analysis will determine which proteins are important for pilus assembly and recognition of acceptor or donor cells. Once the receptor in the pilus is identified, the component(s) will be identified which triggers the signal for aggregation, surface attachment and initiation of DNA transfer. A set of genes downstream of the pili operon might be involved in homologous recombination of exchanged DNA into the Sulfolobus chromosome. Deletion mutant strains of these genes will be used in conjugation assays to show their involvement in UV light induced DNA repair. At the end of this project we aim to elucidate the mechanism how the UV induced pili are involved in cell aggregation, DNA exchange and DNA repair by homologous recombination.