On page 317–320, May et al. use directed evolution to invert the enantioselectivity of hydantoinase, an enzyme used in the industrial production of l-methionine by Escherichia coli. Since hydantoinases are typically selective for the d- over the l-enantiomer, a significant amount of nonproductive intermediates accumulate, reducing the productivity for the l-amino acid. By introducing random mutations into the wild-type gene for hydantoinase, and then screening for gene products with altered enantioselectivity, the researchers converted a d-selective enzyme into an l-selective one. When whole E. coli cells expressed the evolved enzyme, it reduced levels of the unwanted intermediate and boosted productivity of the process.