Genetic fidelity and genome stability in the hyperthermophilic archaeon Sulfolobus acidocaldarius

Hyperthermophilic archaea grow optimally at temperatures that accelerate DNA damage which raises important questions about how these organisms maintain genetic fidelity and genome stability. Archaea in general have reshaped our understanding of the different adaptations of cellular life and their uniqueness justifies their classification into a separate domain of life. The aim of the thesis research presented in this document was to investigate genetic fidelity and genome stability in hyperthermophilic archaea. The approach involved developing genetic assays based on conventional bacterial and eukaryal model systems as well as novel approaches to probe fundamental mechanisms of genome stability at the molecular level. An important component of genetic fidelity, DNA mismatch repair, was investigated in Sulfolobus acidocaldarius. Sulfolobus acidocaldarius was found to repair mismatches formed during homologous recombination (HR), which provides the first in vivo evidence for mismatch repair in hyperthermophilic archaea. However, the events seen in S. acidocaldarius were highly localized, involving individual or short patches of mismatches seen within long tracts of mismatched DNAs, and thus differed from that resulting from conventional mismatch repair. This process contributed to the unique properties of HR in S. acidocaldarius compared to known bacterial and eukaryotic counterparts. Evidence for genome stability and genetic fidelity in S. acidocaldarius was obtained by sequencing and comparing whole genomes of three natural isolates from local populations separated by large distances (∼8200 km). Only 40 polymorphisms were found across all three strains, which suggest a combination of efficient global dispersal and (novel) genetic mechanisms that limit replication errors and chromosomal rearrangements. DNA exchange via conjugation between S. acidocaldarius cells can contribute to this process. Preliminary studies of the size(s) of DNA fragment(s) transferred and direction of transfer show transfer capability of at least 122kb and provide insights into the processing of DNA by the recipient cell following transfer.