Microbial 'Parasites' Meet Climate Change : Marine Cyanobacteria as Viral Puppets

• Main Author: Redgwell, Tamsin
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-2019
• Subjects: Biogeochemistry; Biological oceanography; Chemical Oceanography; Genes; Genetic engineering; Genetics; Metabolism; Microbiology; Mutagenesis; Photosynthesis

Cyanophages play a significant role in oceanic biogeochemistry through lysis of their host and possession of auxiliary metabolic genes (AMGs). AMGs are homologues of host genes that can manipulate the metabolism of their cyanobacterial host during infection, and are widespread in nature. Many cyanophages have been found to contain genes that play roles in photosynthesis, including one of the most well studied AMGs, psbA. PsbA forms part of the core photosystem II complex and is thought to maintain host photosynthesis during infection to optimise phage infection. A major aim of my thesis was to understand the function of the viral psbA and its associated regulatory elements. Components of the cyanophage S-PM2d psbA region were heterologously expressed in a Synechocystis sp. PCC6803 strain lacking its own psbA copies. I showed successful expression of a cyanophage psbA in Synechocystis; however, photophysiological measurements suggest it is not capable of maintaining photosynthesis. The reasons behind this require further investigation. The identity of other AMGs in cyanophages is limited by the lack of a genetic system. Another aim was to create a random chemical mutagenesis system to create mutants of cyanophages and identify novel AMGs. I successfully used hydroxylamine mutagenesis to create mutants of S-PM2d with SNPs identified using high throughput sequencing. I characterised these mutants phenotypically, leading to the identification of novel gene functions, including a SNP in the S-PM2d psbA gene causing an amino acid change. This mutant shows markedly different infection kinetics compared to wild type. This thesis makes an important contribution towards our understanding of how cyanophages manipulate host metabolism, through analysing the function of the cyanophage encoded psbA gene. Additionally, this work has led to the identification of novel gene functions through chemical mutagenesis. Through this we have increased our understanding of how cyanophages interact with their cyanobacterial hosts.