UC San Diego

Marine Synechococcus is an abundant, globally distributed group of picocyanobacteria that are highly diverse, with at least ten subclades described. Copper can be both a micronutrient and a toxicant and of the main phytoplankton groups marine Synechococcus is the most sensitive to copper toxicity, however, there are not many genes identified that are involved in copper response in marine Synechococcus. Global expression microarrays and copper growth assays were used to compare copper stress response between coastal and open ocean strains of marine Synechococcus and found that coastal strains are more tolerant to copper stress and that in one coastal strain the source of this tolerance may lie in its horizontally transferred genomic regions. This was further investigated through functional characterization of two copper- responsive genes in genomic islands. Through inactivation, both genes were found to provide copper tolerance and one of the genes was more abundant in the winter months at a coastal monitoring site. Two genes that were commonly induced by the coastal and open ocean strains were also characterized. One gene of unknown function that may bind copper was found to be involved in copper tolerance. The other gene, putative Deg-protease, was found to be essential for alkaline phosphatase induction and for outer membrane reorganization. Synechococcus clade IV is an important coastally abundant clade and clade IV representative CC9902 is missing some genes that were copper-responsive in the other two strains. Proteome and transcriptome analyses of CC9902 were done following copper stress and validated transcriptional copper stress response at the protein level as well as identified unique and common responses for this strain. Response of natural assemblages of coastal marine Synechococcus were assessed through transcriptional response to copper as well as shifts in diversity of the Synechococcus community following copper addition and verified several copper responsive genes from culture studies and furthermore found that a unique population was enriched following copper addition. For this dissertation, genes and pathways involved in marine Synechococcus copper stress response were identified and characterized, contributing to our understanding of the ecology and physiology of this globally important group with regards to this environmentally relevant metal