All life runs on 20 amino acids. These cells run key machinery on just 19

Scientists equipped Escherichia coli (example pictured) with ribosomes that lacked the amino acid isoleucine. Credit: James Cavallini/Science Photo Library All life on Earth depends on the same molecular alphabet: 20 amino acids that cells string together to make proteins. But now, scientists have reengineered bacteria to run a core part of their cellular machinery with just 19 of those amino acids — a feat akin to rewriting one act of a Shakespearean play without a common letter like “R” while …