Scientists Engineer Bacteria to Work With 19 Amino Acids

Scientists just proved that life doesn't absolutely need all 20 of its traditional building blocks, taking a major step toward understanding how biology itself evolved.

Researchers from Columbia and Harvard successfully engineered parts of E. coli bacteria to work without isoleucine, one of the 20 amino acids that every living thing on Earth has used for billions of years. They focused on the ribosome, the cell's protein-making machine that's essential for life itself.

The team started by testing which amino acid they could most easily eliminate. Isoleucine stood out because it's chemically similar to two others (leucine and valine), and evolution had already shown it could often be swapped out in related species.

Their first experiments were encouraging. When they replaced isoleucine with valine in 36 essential genes, about half worked just fine. Some cells even tolerated the change in 45 different positions within a single protein.

But the real challenge came with redesigning the ribosome. The researchers tested swapping isoleucine for valine in 50 different ribosome proteins individually. While 18 worked perfectly, others caused problems or killed the cells entirely.

Here's where modern technology made the difference. The team used AI-powered protein design software to create new versions of the problematic proteins. Through iterative testing with four different programs, they successfully redesigned nearly all of them to work without isoleucine.

The ultimate test involved replacing all the genes in one part of the ribosome at once. The researchers tackled the small subunit, which contains 21 proteins clustered together on a 10,000-base stretch of DNA. They successfully replaced 17 of these genes simultaneously, though cells grew more slowly and replacing 18 proved fatal.

Why This Inspires

This research isn't just about removing an amino acid. It's about understanding life's flexibility and origins. Before all life on Earth shared a common ancestor, early organisms likely experimented with different genetic codes and simpler biology.

By showing we can engineer cells to work with fewer building blocks, scientists are proving that alternative forms of life are possible. This knowledge could help us understand how the first living things emerged from chemistry, and what other forms biology might take.

The fact that AI tools have matured enough to make this possible is equally exciting. Just a few years ago, redesigning dozens of proteins this way would have been nearly impossible.

While these bacteria grow more slowly without isoleucine, they do grow, proving that life's complexity might be more negotiable than we thought.