Abstract
Bioengineering advances have made it possible to fundamentally alter the genetic codes of organisms. However, the evolutionary consequences of expanding an organism's genetic code with a noncanonical amino acid are poorly understood. Here we show that bacteriophages evolved on a host that incorporates 3-iodotyrosine at the amber stop codon acquire neutral and beneficial mutations to this new amino acid in their proteins, demonstrating that an expanded genetic code increases evolvability.