A team led by Professor Kate Adamala at the University of Minnesota has built SpudCell, a synthetic cell constructed entirely from known chemical components that is capable of performing a complete cell cycle, growing, replicating its genome, dividing, and undergoing selection and competition across multiple generations. The work, detailed in a preprint posted to bioRxiv by Nathaniel J. Gaut, Christopher Deich, Brock Cash, Tanner Hoog, Aaron E. Engelhart, and Katarzyna P. Adamala of the university’s Department of Genetics, Cell Biology and Development, marks what the researchers describe as the first time a fully bottom-up synthetic system has demonstrated this complete cycle.
A cell built from the ground up
SpudCell contains 36 purified enzymes, a roughly 90,000 base pair genome distributed across multiple separate DNA molecules, and a lipid membrane. What distinguishes SpudCell from earlier efforts in the field is its construction method: rather than starting with a living cell and stripping away non-essential components, as prior minimal-cell research has done, SpudCell is assembled entirely from individually purified, non-living parts. This bottom-up approach means every component in the system, and its exact concentration, is known from the moment of formation, giving researchers an unusually precise view of what is happening inside the cell at any given time.
Genetically controlled feeding replaces internal metabolism
One of SpudCell’s central innovations is how it grows. Rather than manufacturing its own nutrients through internal metabolism, a process that in natural cells requires hundreds of genes encoding metabolic enzymes, SpudCell grows by fusing with small “feeder liposomes” that deliver lipids for membrane growth along with nutrients including ribosomes, enzymes, and small molecules.
This fusion is directly controlled by the cell’s own genome. SpudCell produces a protein, using its own DNA, that locks onto the feeder liposome’s membrane to trigger fusion. Because the cell’s DNA governs whether this fusion protein is made, the genome directly determines whether SpudCell can feed, how quickly it grows, and how large it ultimately becomes. By outsourcing nutrient production to external feeder liposomes rather than building the full metabolic machinery natural cells rely on, SpudCell is able to complete an entire cell cycle using a genome far smaller than would otherwise be required.
Dividing without a cytoskeleton
Natural cells rely on an internal scaffolding system, the cytoskeleton, to physically divide. Building a functional cytoskeleton from scratch has long been a major bottleneck in synthetic cell research, since it requires dozens of proteins working in precise coordination. SpudCell avoids this challenge entirely: rather than using scaffolding to pull itself apart, the same surface protein involved in feeding accumulates on the cell’s membrane until the resulting mechanical stress causes the membrane to split.
Because this is the same protein responsible for feeding, cells that produce more of it not only grow faster but also divide more efficiently, creating a direct link between the genome and the cell’s reproductive success, without requiring any separate cytoskeletal system.
Selection and competition in a synthetic system
To test whether SpudCell could exhibit evolutionary dynamics, researchers introduced a genetic change that increased production of the fusion protein. Cells carrying this change grew faster and produced more offspring than the original population, and after five generations, the faster-growing variant had outcompeted the original line entirely. This competitive advantage grew even larger under conditions of nutrient scarcity, demonstrating that selection and competition, hallmarks typically associated with living organisms, can operate within a fully synthetic chemical system.
Genome architecture smaller than theoretical minimums
SpudCell’s roughly 90,000 base pair genome is distributed across several separate DNA plasmids rather than existing as a single chromosome, with each plasmid encoding specific functions. This modular architecture allows individual functions within the system to be modified independently of one another, a practical advantage for future engineering efforts. Notably, prior theoretical analysis had estimated that a minimal genome for a living cell would need to be at least 113 kilobase pairs; SpudCell’s genome, at roughly 90 kbp, falls below this previously proposed theoretical minimum.
Built on a fully defined protein expression system
For protein expression, SpudCell relies on the PURE (Protein Synthesis Using Recombinant Elements) system, a defined mixture of 36 purified enzymes derived from E. coli bacteria, including ribosomes, that reads DNA and synthesizes proteins. This represents a departure from earlier synthetic cell approaches that relied on crude bacterial cell extracts containing many unknown or uncharacterized components. Because every component in PURE, and its concentration, is precisely known, researchers using this system can track exactly what is happening inside SpudCell at a molecular level, rather than working with a partially opaque biochemical mixture.
Physically, SpudCell takes the form of a liposome, a hollow sphere made of lipid molecules similar to those that form natural cell membranes, containing the DNA genome and the PURE expression system inside. All of the proteins SpudCell needs to function are produced from within the cell, using its own genome and the enclosed PURE machinery, rather than being introduced from outside.
The molecular mechanism behind feeding
The specific molecular link enabling SpudCell to feed relies on a protein called α-hemolysin. When SpudCell produces this protein from its own DNA, the protein inserts itself directly into the cell’s membrane, spanning all the way through it. A chemical tag attached to the protein extends out from the membrane surface, where it binds to matching molecular hooks on feeder liposomes, triggering the fusion event that delivers new lipids and nutrients into SpudCell.
Remaining challenges on the path to greater autonomy
While the researchers describe SpudCell as demonstrating that many of the core processes of life can be reconstituted from fully specified, individually purified components, they also identify several significant challenges still to be addressed. Chief among them is the system’s current reliance on ribosomes sourced from E. coli bacteria; without the ability to build its own ribosomes, SpudCell can only run for five to ten generations before its protein-making machinery degrades. Building ribosomes from genetic instructions would require synthesizing dozens of proteins and RNA molecules and getting them to assemble correctly, a substantial engineering challenge in its own right.
A second challenge involves genome distribution during division. After five generations, only about 30% of daughter cells inherit the complete set of DNA plasmids needed for full function. Natural cells solve this problem using cytoskeletal machinery that actively pulls chromosomes apart during division, a mechanism SpudCell currently lacks. Improving genome inheritance will likely require more sophisticated division mechanisms than the current membrane-stress-driven approach.
Finally, the researchers note that SpudCell remains dependent on external inputs beyond feeder liposomes, including streptavidin and molecular linker proteins required for division, both of which must currently be supplied from outside the system. Reducing this dependence and moving toward a more autonomous synthetic cell will require building metabolic pathways capable of synthesizing these components internally from simpler starting materials.
A foundation for future synthetic biology
Taken together, the researchers describe SpudCell’s nanovesicle-based feeding approach as providing a foundation on which future synthetic cell research can build, even as substantial work remains to achieve greater autonomy, more reliable genome inheritance, and a fully self-sustaining protein synthesis system. As the first bottom-up synthetic system to demonstrate a complete cell cycle, including growth, division, and evolutionary competition, SpudCell represents a notable step toward understanding which components are truly essential for cellular life, and which functions can be offloaded to external systems without preventing a cell-like system from growing, reproducing, and evolving.
Researchers interested in the full technical details, including genome architecture, protein expression methodology, and experimental data on selection and competition, can access the complete manuscript through the preprint posted on bioRxiv.