Fig. 6
Optimising phenylalanine production by minimising degradation and competition from tyrosine biosynthesis. KmASR.047′s aromatic amino acid biosynthetic flux was redirected by knocking down TYR1 expression using a weak promoter (ASR.047kd, ASR.047kd2), and restricting metabolism by knocking out the aromatic aminotransferase KmARO8 (KmASR.112). The most effective promoter knockdown, the REV1 promoter, was combined in the latter to produce KmASR.117. With the increased capacity for phenylalanine synthesis in this strain, we increased phenylalanine synthesis more by further supplying precursors using either KmENO1 or a combination of heterologous enzymes alongside KmARO3fbr to better utilise increased precursor levels. Data are the mean ± s.d. of at least three biological replicates. trains producing significantly higher amounts of 2-PE relative to that produced by KmASR.047 as determined by an independent t-test are marked by an asterisk (*p < 0.05) or a hash (#p < 0.005), and those producing significantly more 2-PE relative to KmASR.0117 are marked with a dagger (†p < 0.05). Data are the mean ± s.d. of at least three biological replicates. Km: Kluyveromyces marxianus, Bb: Bifidobacterium breve, Se: Salmonella enterica