Some bacteria navigate using the Earth’s magnetic field. They produce chains of iron-rich nanoparticles inside their own cells, using them like a biological compass to orient themselves in low-oxygen environments. For decades, scientists have studied these organisms out of pure curiosity. Now, engineers at Aston University in Birmingham are turning that navigation system into a tool for fighting cancer.
The project, led by Dr Alfred Fernandez-Castane, reader in chemical and biochemical engineering at Aston, has been awarded €1.2m through the Marie Skłodowska-Curie Actions (MSCA) Staff Exchanges programme. The funding supports 18 European and US partner organisations and 67 researchers - 34 at an early-career stage - across disciplines including biochemical engineering, oncology, immunology, and materials science. The goal is to develop a magnetobot cancer treatment: a system in which living magnetic bacteria are engineered to carry anti-cancer payloads and delivered precisely to tumours under the guidance of external magnetic fields.
The bacteria at the centre of the project are magnetotactic organisms found in lakes, rivers, sediments, and other low-oxygen environments. What makes them useful is the magnetosome: a membrane-enclosed nanoparticle of magnetite (Fe₃O₄) or greigite (Fe₃S₄) that the bacterium synthesises internally with remarkable precision. Magnetosomes are typically 30-120 nanometres in diameter and are arranged in a chain along the length of the cell. The chain acts as a biological compass needle, aligning the organism with magnetic field lines and allowing it to swim toward lower oxygen concentrations - a behaviour called magnetotaxis.
The engineering challenge is to redirect this natural navigational ability from detecting oxygen gradients to detecting tumours. The plan, as outlined by the Aston team, involves attaching “payloads” to the surface of the bacteria - anti-cancer drugs, drug-loaded liposomes, or immune-stimulating materials - and then using external magnetic fields to guide the loaded organisms through the bloodstream to the site of a tumour.
Once there, the bacteria can be tracked using magnetic resonance imaging (MRI) because the iron nanoparticles they carry serve as contrast agents. This makes the system simultaneously diagnostic and therapeutic. The technical term for this combination is theranostics - a somewhat inelegant portmanteau that captures precisely what the technology does: diagnosis and therapy in a single platform.
The cancers being targeted are among the most difficult to treat with conventional approaches. Pancreatic, breast, lung, and colorectal cancers all present challenges for standard chemotherapy, which distributes drugs throughout the body rather than concentrating them at the tumour. The resulting toxicity to healthy tissue is one of the main reasons cancer treatment is so gruelling for patients. A magnetobot cancer treatment that delivers drugs directly to the tumour and reduces systemic exposure could significantly change that calculus.
Aston’s specific responsibilities within the wider collaboration focus on the biological production side. Growing magnetotactic bacteria at scale is not straightforward. The organisms are fastidious. They require precisely controlled oxygen concentrations, carefully calibrated nutrient supplies, and specific temperature and pH conditions. Producing too much oxygen, the magnetosomes fail to form. Produce too little, and growth stalls. The team will work on bioreactor design, process monitoring using digital sensors, and the scale-up of bacterial production from laboratory flasks to volumes that might eventually be clinically relevant.
This is not the first time the Aston group has worked with magnetotactic bacteria. Previous projects used the organisms to recover proteins from blood serum and extract critical metals from industrial waste streams - applications that exploit magnetosomes’ magnetic properties for purposes entirely unrelated to medicine. That experience with bioreactor control and bacterial production gives the team a practical foundation for the new project.
Engineering Deep Dive: The Physics and Biology Behind Magnetobot Cancer Treatment
The magnetobot cancer treatment concept sits at the junction of magnetic physics, cell biology, and chemical engineering. Breaking down each component helps clarify both the opportunity and the remaining engineering challenges.
Magnetite (Fe₃O₄) is a ferrimagnetic material: its iron atoms are arranged in two sublattices with opposing magnetic moments, but the moments do not cancel completely, leaving a net magnetic moment per unit cell. At the nanoscale, magnetite particles can exist as single-domain magnets - meaning the entire particle acts as one magnetic dipole rather than being divided into multiple domains. This makes individual magnetosome nanoparticles very efficient magnetic agents. A chain of 15-20 magnetosomes produces a magnetic moment large enough to align the bacterium with geomagnetic field lines of just 50 microtesla (the Earth’s surface field strength).
External magnetic fields used to guide the bacteria to tumours would be far stronger - typically in the range of tens to hundreds of millitesla, achievable with permanent neodymium magnets or clinical electromagnets placed outside the body. At these field strengths, the bacteria experience a torque that aligns them with the field direction. By moving the magnet, or by using arrays of electromagnets to steer the field, researchers can, in principle, guide a population of bacteria along a chosen path through tissue.
The physics of magnetic guidance through biological tissue is complicated by blood flow, tissue density, and the branching geometry of tumour vasculature. Tumours develop their own blood vessel networks through a process called angiogenesis, but these vessels are typically disorganised and leaky. This is both a problem and an opportunity: the leakiness means nanoparticles (and bacteria-sized objects) can escape from blood vessels into tumour tissue through gaps that are too small for larger immune cells. This phenomenon, known as the enhanced permeability and retention (EPR) effect, is one of the reasons nanomedicine has attracted such interest as a cancer treatment strategy.
Liposomes - the drug carriers that may be attached to the bacteria’s surface - are spherical vesicles made from phospholipid bilayers, structurally similar to cell membranes. They can encapsulate water-soluble drugs in their interior or incorporate fat-soluble drugs within their lipid bilayer. Liposomes have been used in clinical cancer treatment since the 1990s, most notably in liposomal doxorubicin formulations, because they reduce the cardiac toxicity associated with doxorubicin when administered in free form. Attaching liposomes to magnetotactic bacteria would combine the drug-carrying capacity and biocompatibility of established liposome technology with the bacteria’s magnetic guidance.
The role of MRI in tracking bacteria connects to a different branch of physics. MRI relies on the magnetic resonance of hydrogen nuclei (protons) in water molecules. Iron oxide nanoparticles act as T2 contrast agents: they create local magnetic field inhomogeneities that cause nearby protons to dephase more rapidly, darkening the MRI signal in regions where the bacteria accumulate. Clinical iron oxide contrast agents such as ferumoxytol are already approved for certain MRI applications. The magnetosomes in magnetotactic bacteria are structurally similar, meaning that existing MRI infrastructure could, in principle, detect the bacterial payload without requiring new imaging equipment.
The bioreactor challenge that the Aston team is addressing connects chemical engineering to biology. Magnetotactic bacteria produce magnetosomes only under microaerobic conditions - oxygen concentrations significantly below atmospheric levels but above zero. Too much oxygen suppresses the expression of genes encoding magnetosome synthesis proteins; too little kills the bacteria. Controlling dissolved oxygen in a bioreactor with the precision required means using fast-response dissolved oxygen sensors, feedback-controlled gas sparging, and carefully characterised growth models. The Aston group’s experience from their earlier projects on protein recovery and metal extraction means they already have some of this instrumentation and process knowledge in place.
Scale-up adds another layer. The volumetric productivity of magnetotactic bacteria - the mass of biomass (and magnetosomes) produced per litre of culture per hour - is lower than for common industrial bacteria like Escherichia coli. Increasing productivity without losing magnetosome quality requires understanding how bacterial growth rate, iron availability, and oxygen tension interact. Digital monitoring systems that track multiple parameters simultaneously and feed data into predictive models will be central to this work and to establishing whether clinical-scale production is economically viable.
Magnetobot cancer treatment is not yet a clinical therapy. The Aston project is at the engineering and biological research stage, with the immediate goals being reliable bacterial production and proof-of-concept targeting in laboratory models. But the logic of the approach - use the organism’s own magnetic navigation, redirect it with an external field, track it with existing imaging infrastructure - is sound. The components already exist. The question is whether they can be brought together in a system robust enough to work in a patient.
