Dr George B Stefano | Mitochondria Reconsidered: Unmasking the Ancient Bacterial Legacy in Human Health

Although often described simply as the cell’s powerhouse, mitochondria began life as bacteria and still carry many bacterial traits. Dr George Stefano, Visiting Professor at Charles University, Prague, explores whether mitochondria should be seen not only as symbiotic partners but also as the most successful chronic infection in history. He highlights how this perspective sheds light on human resilience, viral tolerance, and long-term health. By reframing mitochondria in this way, Dr Stefano and colleagues invite a broader conversation about ageing, disease, and the fine balance between host and microbe that continues to shape human biology today.

Background: From Ancient Bacteria to Cellular Powerhouses

Mitochondria originated more than a billion years ago when an early cell engulfed a bacterium that survived instead of being digested. Over time, this partnership deepened. Most bacterial genes moved into the host cell’s nucleus, while the bacteria themselves evolved into mitochondria. Despite this shift, mitochondria still look and behave like bacteria in many ways. Dr Stefano points out that this ancestry means mitochondria may not simply be harmless companions, but instead represent a tolerated long-term infection that became essential for survival.

New Insights into Mitochondria’s Role

Modern research has revealed that mitochondria are much more than energy suppliers. They help repair DNA, regulate cell death, and manage the body’s immune defences. In bats, for example, mitochondria help balance strong antiviral responses with low inflammation, allowing them to live with viruses that are deadly to other species. Dr Stefano explains that these discoveries show mitochondria as active decision-makers in health, shaping how organisms respond to stress, infection, and ageing.

Gaps in How We Think About Mitochondria

For decades, mitochondria have been described in textbooks as stable partners in cells. This narrative overlooks their bacterial heritage and underestimates their potential for dysfunction. Dr Stefano argues that by continuing to think of mitochondria only as symbionts, we miss the complexity of their role. Like bacteria, they replicate independently, carry their own DNA, and can even survive outside cells in human blood. These traits make them look less like harmless passengers and more like bacteria that never fully left their infectious roots.

Mitochondrial Quality and Human Disease

When mitochondria work well, they fuel cells and help maintain balance. But when quality control fails, problems arise. Damaged mitochondria can leak signals that trigger inflammation, contribute to neurodegeneration, or drive metabolic diseases like diabetes. Antibiotics, which target bacteria, can also damage mitochondria by mistake, linking treatment side effects to their shared ancestry. Dr Stefano and team highlight that the quality of mitochondrial function is central to human health and that overlooking this connection risks misinterpreting disease.

A Total System Perspective on Life and Illness

Dr Stefano and colleagues propose a ‘total system’ view of mitochondria, where their actions ripple through every aspect of biology. They are involved in immunity, energy, stress responses, and even how we age. Seeing mitochondria as both essential partners and persistent bacterial lodgers allows us to better understand why they influence so many diseases. Just as histology depends on every step of tissue handling, human health depends on the continuous fine-tuning of mitochondrial behaviour.

What Does the Future Hold: Reframing Mitochondrial Research

Dr Stefano calls for a revaluation of mitochondria’s place in science and medicine. His aim is not to dismiss their life-giving role but to invite dialogue on how their bacterial legacy still shapes us. By recognising mitochondria as both friend and infection, researchers can explore new ways to strengthen resilience, prevent disease, and rethink ageing. This perspective may lead to treatments that protect mitochondria, reduce chronic illness, and help humans live longer, healthier lives.