Open Collections

George, Emma E.

University of British Columbia

Genome evolution of bacterial symbionts has led to different evolutionary outcomes including stable symbiosis, extinction, and rarely organelle formation (e.g., mitochondria and plastids). Symbiont genome evolution has mostly been studied in animal endosymbionts, but microbial eukaryotes (protists) contain diverse symbionts with various functional roles and evolutionary trajectories. However, symbiont genome reduction and functional relationships with protist hosts are largely unexplored. Additionally, how bacteriophage (phage) infection impacts symbiont-eukaryotic interactions and symbiont genome evolution is relatively unknown in protists. Here, I used DNA and RNA sequencing and microscopy methods to characterize endosymbionts and symbiont-infecting phages from diverse protists, including marine diplonemids, freshwater cryptomonads, and termite gut parabasalids. The diplonemid and cryptomonad endosymbionts belonged to intracellular bacterial groups Rickettsiales and Holosporaceae (Alphaproteobacteria), and they harboured an arsenal of proteins with putative eukaryotic-interacting domains (e.g., leucine-rich repeats and ankyrin repeats). The diplonemid endosymbionts had extremely small genomes with reduced metabolic potential compared to other Rickettsiales and Holosporaceae endosymbionts. Despite this, they retained a small cluster of gene transfer agent (GTA) genes also highly conserved in Rickettsiales and Holosporaceae, and evidence of GTA gene expression was found. An endosymbiont-infecting phage was also characterized in an undescribed Cryptomonas species, and the temperate phage encoded several eukaryotic-interacting proteins. Finally, phages from the hindgut of wood-feeding insects were sequenced and predicted to infect protist endosymbionts and hindgut bacteria. Overall, this work highlights the complex interactions between phages, bacteria and protists from diverse environments and provides valuable insights into the evolution of all three groups.

Text

2022-08-24

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/82492

Botany

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/