Design of a Bio-Based Adipic Acid Microbial Cell Factory: The Challenging Choice of Microbial Host and Metabolic Pathway

Adipic acid is a six carbon- dicarboxylic acid used mainly as a building block in the nylon industry for the synthesis of nylon 6,6. According to the report (Bioenergy Task 42, Biorefinery) released by the International Energy Agency (IEA), adipic acid is the dicarboxylic acid derived from fossil raw materials with the highest annual production volumes. The aim of this study is to engineer a microbial host that would be able to convert sugars deriving from renewable bio-based materials, such as forest residues, into adipic acid. In this work, we present the metabolic pathway of our choice, using lysine as substrate. Preliminary results on the characterization of enzymes we identified as good candidates to catalyze specific metabolic steps are presented. Furthermore, we show the results of a study aimed to define the tolerance to adipic acid of an array of potential microbial hosts, including three yeast species, the filamentous fungus Aspergillus niger and bacterial species, such as Escherichia coli and Corynebacterium glutamicum. The results of this study give crucial indications on the choice of the most suitable microbial host to be considered for the design of an adipic acid microbial cell factory.