Pseudomonas putida as a platform for the synthesis of aromatic compounds

Aromatic compounds such as l-phenylalanine, 2-phenylethanol and trans-cinnamate are aromatic compounds of industrial interest. Current trends support replacement of chemical synthesis of these compounds by 'green' alternatives produced in microbial cell factories. The solvent-tolerant Pseudomonas putida DOT-T1E strain was genetically modified to produce up to 1 g l-1 of l-phenylalanine. In order to engineer this strain, we carried out the following stepwise process: (1) we selected random mutants that are resistant to toxic phenylalanine analogues; (2) we then deleted up to five genes belonging to phenylalanine metabolism pathways, which greatly diminished the internal metabolism of phenylalanine; and (3) in these mutants, we overexpressed the pheAfbr gene, which encodes a recombinant variant of PheA that is insensitive to feedback inhibition by phenylalanine. Furthermore, by introducing new genes, we were able to further extend the diversity of compounds produced. Introduction of histidinol phosphate transferase (PP_0967), phenylpyruvate decarboxylase (kdc) and an alcohol dehydrogenase (adh) enabled the strain to produce up to 180 mg l-1 2-phenylethanol. When phenylalanine ammonia lyase (pal) was introduced, the resulting strain produced up to 200 mg l-1 of trans-cinnamate. These results demonstrate that P. putida can serve as a promising microbial cell factory for the production of l-phenylalanine and related compounds.