The curious case of vanishing mitochondria

Area of Science:

• Eukaryotic cell biology
• Evolutionary biology
• Microbial genomics

Background:

• Mitochondria are vital for eukaryotic energy metabolism and essential functions like iron-sulfur cluster assembly.
• Mitochondrion-related organelles (MROs) are reduced forms found in low-oxygen environments, often lacking ATP production but retaining other functions.
• The existence of eukaryotes entirely lacking mitochondria or MROs was previously unknown.

Discussion:

• Monocercomonoides represents the first characterized *bona fide* amitochondriate eukaryote, lacking all canonical mitochondrial proteins.
• This organism utilizes a bacterial sulfur mobilization (SUF) system instead of the canonical mitochondrial iron-sulfur cluster assembly (ISC) pathway.
• This finding highlights the remarkable plasticity of eukaryotic cell evolution and metabolic adaptation.

Key Insights:

• Discovery of a eukaryote completely devoid of mitochondria and MROs.
• Identification of a functional bacterial sulfur mobilization (SUF) system replacing the mitochondrial iron-sulfur cluster assembly (ISC) pathway.
• Demonstration of alternative pathways for essential cellular functions in eukaryotes.

Outlook:

• Further investigation into the evolutionary origins and mechanisms of the SUF system in amitochondriate eukaryotes.
• Exploring other microbial eukaryotes for similar mitochondrial absences and alternative metabolic strategies.
• Re-evaluating the definition and essentiality of mitochondria across the eukaryotic domain.