show Abstracthide AbstractSelection based study where E. coli tryptophan auxotrophs harboring heterologously expressed beta subunits of the tryptophan synthases of Thermotoga maritima (TmTrpB) were grown in exogenous indole. E. coli harboring more active TmTrpBs, which convert indole to tryptophan, grow at a faster rate. Sequencing data from this library generates a fitness landscape mapping protein sequence to growth rate.