Mutant and wild-type C. sporogenes were incubated with phenylalanine, tyrosine and tryptophan derivatives of each of the four coloured compounds and metabolites were assayed by LC-MS/MS. Compared to wild-type, the fldH, fldC and acdA mutants were deficient in reductive metabolism of phenylalanine, tyrosine and tryptophan (rows 1–4, column 5, red and green traces). Relative to wild-type, the porA mutant was deficient in oxidative metabolism of phenylalanine and tyrosine, but not tryptophan (rows 1 and 5, column 1, red and green traces). Representative chromatograms from n = 3 biological replicates. Phe, phenyl; 4-OH-Phe, 4-hydroxyphenyl.