The key finding
Mitochondria, the energy-producing structures inside our cells, possess a distinctive inner membrane architecture with elaborate folds called cristae. A 2025 review in the Journal of Cell Science synthesizes evidence that these specialized membranes—along with their unique lipid composition—likely evolved from structures found in ancient alphaproteobacteria. The review highlights how protein complexes like MICOS (mitochondrial contact site and cristae-organizing system) have homologs in modern bacteria that create similar membrane structures called intracytoplasmic membranes (ICMs). This suggests that when an Asgard archaea-related host cell engulfed an alphaproteobacterium over a billion years ago, the machinery for building complex internal membranes was already present and became adapted for mitochondrial function.
What the study looked like
This is a comprehensive review article that synthesizes findings from phylogenetic studies, genomic analyses, and metagenomic data rather than presenting new experimental results. The authors examined evolutionary relationships between modern mitochondrial proteins and their bacterial ancestors, comparing the structure and function of cristae in eukaryotic mitochondria with ICMs in diverse extant alphaproteobacteria. They analyzed both the protein machinery that shapes these membranes (like MICOS complexes) and the enzymes responsible for synthesizing mitochondrial-specific phospholipids. The review draws on recent advancements in multiple fields—evolutionary biology, structural biology, lipid biochemistry, and comparative genomics—to trace how mitochondrial membranes became specialized during eukaryogenesis, the process by which eukaryotic cells first arose.
Why researchers think this happened
The authors propose that mitochondrial membrane specialization occurred through co-evolution of lipid composition and protein architecture. When the ancestral alphaproteobacterium became an endosymbiont, it already possessed proteins capable of creating internal membrane structures. Over evolutionary time, these proteins adapted alongside newly evolving lipid synthesis machinery to create the cristae architecture we see today. The review suggests this wasn’t a sudden invention but rather a gradual refinement—the bacterial ancestor’s ICM-forming proteins provided a foundation that became increasingly specialized. The concurrent evolution of unique mitochondrial phospholipids and cristae-shaping proteins allowed mitochondria to maximize their surface area for energy production while maintaining structural integrity. This co-evolution model explains why mitochondrial membranes differ so dramatically from other cellular membranes: both the lipid building blocks and the protein scaffolding evolved together to support the intense metabolic demands of these organelles.
How to read this carefully
As a review article rather than original research, this work synthesizes existing evidence and proposes evolutionary models based on comparative analyses. The actual events of eukaryogenesis occurred over a billion years ago, making direct observation impossible—scientists must infer what happened by comparing modern organisms and their genomes. While the presence of MICOS-like proteins in alphaproteobacteria provides compelling evidence for evolutionary continuity, the exact sequence of events remains uncertain. The review also notes that the origins of lipid synthesis machinery have been “less explored” than protein complexes, meaning some aspects of the model require further investigation. Phylogenetic analyses can reveal relationships but cannot definitively prove causation or recreate the precise environmental conditions that drove these evolutionary changes. Readers should understand this represents our current best model, subject to revision as new genomic and experimental data emerge.
What this means for everyday life
Understanding mitochondrial evolution helps explain why these organelles are so central to human health and disease. When mitochondrial membranes malfunction—whether due to genetic mutations affecting cristae-shaping proteins or lipid synthesis—the consequences can include metabolic disorders, neurodegenerative diseases, and aging-related decline. The fact that our mitochondria retain architectural features from their bacterial ancestors highlights how evolution builds on existing structures rather than designing from scratch. This research reminds us that the efficient energy production powering every moment of our lives depends on billion-year-old membrane structures refined over countless generations. For scientists developing therapies for mitochondrial diseases, knowing which components are ancient versus newly evolved in eukaryotes might inform which systems can be safely targeted. While this knowledge won’t change your daily routine, it deepens appreciation for the remarkable evolutionary journey that made complex life—including us—possible.