Investigations on the Mitochondrial Protein Composition of Microbial Eukaryotes from Diverse Physical Environments

Ciliates are a group of microbial eukaryotes that are found in diverse environments, which have been identified to contain different classes of mitochondria. It is understood that mitochondria have modified their functions overtime depending on the environment of their host; these differences in adaptations allow mitochondria to be classified into five different groups/classes. Four of these classes generate adenosine triphosphate (ATP), while the fifth has undergone evolutionary reduction having no apparent role in ATP synthesis. The aim of this project was to evaluate the diversity of these organelles in ciliates. This was carried out using computational methods, where we analysed and translated genomic and transcriptomic data collected from 27 ciliates found in diverse environments. The ciliate data were searched against a database of nine different mitochondrial proteomes and multiple anaerobically functioning proteins in order to assemble the potential mitochondrial proteome for each organism based on sequence similarity.

Our method allowed the prediction of mitochondrial class diversity within one "group" of eukaryotes, identifying all five classes throughout the 27 ciliates, including the proposal of a potential mitosome present within the rumen-living ciliate Entodinium caudatum, as well as confirming the existence of hydrogenosomes present within Polyplastron multivesiculatum. By analysing functional proteins of the citric acid cycle and the electron transport chain, as well as identifying any proteins that function in anaerobic conditions; we have been able to make clear distinctions between each mitochondrial class and provide a strong likelihood that all five mitochondrial classes are present across the ciliate clade,

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along with the possible presence of intermediated organelles that do not fit the already classified groups.

This diversity of mitochondrial class seen throughout the ciliate clade further supports the claim of anaerobically functioning mitochondria potentially being the ancestral mitochondria of ciliates.