Introduction of a stress-responsive gene, yggG, enhances the yield of l-phenylalanine with decreased acetic acid production in a recombinant Escherichia coli

A stress-responsive gene, yggG, was introduced into an l-phenylalanine producer, Escherichia coli AJ12741. In shake-flask culture, the yggG-containing recombinant strain (named AJ12741/pHYGG) produced 6.4 g l-phenylalanine l−1 at the end of culture and its yield on glucose was 0.16 g l-phenylalanine g glucose−1. These values are much higher than those of the original AJ12741 strain (3.7 g l-phenylalanine l−1 and 0.09 g l-phenylalanine g glucose−1, respectively). On the other hand, AJ12741/pHYGG strain produced only 4.5 g acetic acid l−1 and its yield on glucose was about a half of that of the AJ12741 culture. Analysis of gene expression revealed that in late growth phase, the expression levels of genes involved in acetic acid production (pta, ackA, and poxB) were relatively low in AJ12741/pHYGG cells. In particular, the level of poxB expression in AJ12741/pHYGG strains was one-seventh of that of the original strain. These results suggest that the formation of a bottleneck for acetic acid production brings about a metabolic flow favorable to l-phenylalanine synthesis in the recombinant strain over-expressing the yggG gene.