From Chlamydomonas reinhardtii to Caenorhabditis elegans: Investigations into the environmental regulation of eukaryotic Cu-handling mechanisms

This dissertation investigated the environmental factors that contribute to eukaryotic Cu homeostasis. Using a single-celled eukaryote, Chlamydomonas reinhardtii, this work expanded upon the knowledge of Cu uptake transporters (CTRs). The noncanonical CTR3 was found to be periplasmic and, despite validating mutant strains for the protein, was not identified to play any role in the accumulation of Cu in conditions that increased expression of CTR3 with CTR1 and CTR2. However, another soluble factor, glutathione (GSH), was found to contribute to Cu accumulation driven by canonical CTRs during Zn deficiency. However, despite this potential for increased accumulation through CTRs, GSH also consistently protected Chlamydomonas from nonessential Ag toxicity. The two canonical CTRs, CTR1 and CTR2, were further distinguished by their varying affinity for Cu during Cu deficient and Zn deficient conditions Therefore, it was concluded that CTR1 and CTR2 are not redundant because they could not substitute for one another’s function. In subsequent investigations, the use of Caenorhabditis elegans allowed for the study of bacterial Cu-resistance responses within a host-microbe system. These investigations identified increasing bacterial Cu-efflux as an environmental factor contributing to the sensitization of host C. elegans to Cu exposures by changing the spatial localization of metal stress within the adult nematode in a tissue specific manner instead of reducing the overall body burden of the metal exposure. Consequently, C. elegans raised on bacterial lawns with reduced bacterial Cu-efflux capacity, achieved by targeted deletions in the cusRS two component system in Escherichia coli, exhibited 1) increased survival, 2) reduced matricidal hatching, 3) improved growth, and 3) a shifted nuclear metal responsive gene (numr-1) reporter to the posterior of the pharynx where Cu accumulated by bacteria is released by the pharyngeal grinder in response to high environmental Cu stress. These investigations present health implications for the increasing Cu resistance observed in bacterial populations due to increased industry and metal deposition and for the compounding challenges facing transition metal homeostasis in these increasingly manmade environments