Exploring the evolution of anaerobes within ciliate class Prostomatea by transcriptomics.

Area of Science:

• Evolutionary Biology
• Microbiology
• Biochemistry

Background:

• Mitochondrion-related organelles (MROs) are crucial for anaerobic eukaryotes surviving in oxygen-deprived environments.
• Ciliate adaptations to anaerobic conditions are often lineage-specific, with limited understanding of MRO metabolic diversity.
• The class Prostomatea, predominantly aerobic, offers a unique system to study the transition from mitochondria to MROs.

Purpose of the Study:

• To investigate the metabolic peculiarities and evolutionary history of MROs in anaerobic ciliate species from the Prostomatea class.
• To explore the convergent evolution of MROs across different ciliate lineages.

Main Methods:

• Transcriptome sequencing of four anaerobic Prostomatea species (Apolagynus and Holophrya).
• Prediction of mitochondrial metabolisms and reconstruction of phylogenomic and SSU rDNA trees.
• Ecological niche mapping and comparison of electron transport chain (ETC) pathways.

Main Results:

• Prostomatea is paraphyletic and closely related to Oligohymenophorea and Plagiopylea.
• Anaerobic Prostomatea species exhibit at least two distinct MRO phenotypes with varied ATP generation strategies (oxidative vs. substrate-level phosphorylation).
• Specific enzymes like ASCT, SCS, AK, and [FeFe] hydrogenase were identified, indicating diverse anaerobic metabolic pathways.

Conclusions:

• The MROs in anaerobic Prostomatea have evolved through repeated convergent evolution.
• This study expands our knowledge of MRO diversity and anaerobic adaptations in ciliates.
• Findings provide insights into the evolutionary trajectory of anaerobic eukaryotes within the Prostomatea class.