La, SoRi2023-05-082023-05-082022https://hdl.handle.net/10539/35470A dissertation submitted in fulfilment of the requirements for the degree of Master of Science to the Faculty of Science, School of Geosciences, University of the Witwatersrand, Johannesburg, 2022Programmed Cell Death (PCD) genetic toolkits and mechanisms of death in prokaryotes, particularly archaea, are poorly understood and whether PCD mediated conflict in eukaryogenesis remains controversial. This study aimed to investigate C14 peptidases, the key effectors of PCD, in archaea and their evolutionary histories prior to eukaryogenesis. Their wide taxonomic distribution and phylogenetic reconstruction revealed that C14 peptidases were present before the divergence of prokaryotes. Furthermore, phyletic pattern and death domain architecture analyses revealed that they were likely associated with pro-survival functions before their co-option in PCD, supporting Ameisen’s ‘original sin’ hypothesis for PCD origins. In vivo analysis to explore potential caspase- and metacaspase-like activity in Halobacterium salinarum under oxidative stress showed negative results, in accordance with PCD being a black queen trait in the microbial loop between H. salinarum and Dunaliella salina. This study provides a detailed evolutionary history of C14 peptidases prior to eukaryogenesis.enDissertation