DNA repair processes are crucial for the growth and survival of all organisms. This is especially true for organisms, that inhabit extreme habitats, like the Antarctic Dry Valleys. The Dry Valleys are one of the coldest and driest desert environments on Earth. The conditions in the Dry Valleys, including high levels of UV radiation, low temperatures, multiple daily freeze-thaw cycles, desiccation, and low nutrient levels, are highly damaging to the genomic DNA of the organisms inhabiting them. The Dry Valleys are dominated by microorganisms, which have a range of adaptations to survive in this extreme environment. Previous studies focus largely on the metabolic adaptation of Dry Valley inhabitants. In this thesis, the DNA repair machinery of bacteria in the Dry Valleys was examined to determine how organisms survive the DNA-damaging conditions. Our understanding of DNA repair and replication in bacteria pathways is largely based on studies of isolated organisms and pathogens, which have been extensively studied. Methods such as metagenomic sequencing allow us to find novel proteins from currently unculturable organisms. In a search for novel DNA repair proteins in bacterial metagenomes from the Dry Valleys, two unique nuclease proteins were chosen for structural and biochemical characterisation. One of these nuclease proteins belongs to the currently uncharacterised protein domain UPF0102. This protein is distantly related to the archaeal Holliday junction resolvases and is a Type II restriction endonuclease type protein. The activity of DV-Hjc and the UPF0102 domain was characterised in vitro using biochemical assays and in vivo in E. coli knockout cells. Biochemical characterisation of the protein showed that the protein has strong binding affinity with double-stranded DNA substrates and Holliday-junction mimicking substrates. The structure of the protein was determined via X-ray crystallography at a resolution of 0.9 Å and structural features were related to its activity, revealing an extensive DNA binding surface and an active site similar to that of archaeal Holliday junction resolvases. The second nuclease characterised in this thesis is part of a unique nuclease-ligase fusion protein and belongs to the nuclease group of MBL-β-CASP proteins. The biochemical characterisation of the protein showed its ability to bind and cleave DNA, specific activity was observed with abasic site substrates.