Genetic characterization of mutants. In 40 mutants, targeted sequencing revealed mutations in lysC, hom, thrC and thrB, with some of the mutations already known from prior work (see text). Mutations that resulted in amino acid exchanges are indicated, along with growth rates and final external lysine titers. The mutation murE-G81E in strain K051 was identified by whole-genome sequencing. The second murE mutation, murE-L121F, was identified by subsequent targeted sequencing. In 15 mutants (plus K051), it was not possible to identify any mutation by site-directed mutagenesis.