Aureobasidium pullulans NRRL 62042 as robust platform for efficient lignin valorization and sustainable cis,cis-muconic acid production

Lignin is a highly abundant source of renewable aromatics, but efficient microbial conversion remains challenging due to the limited substrate tolerance of many microorganisms. In this study, the polyextremotolerant yeast-like fungus Aureobasidium pullulans NRRL 62042 was identified as a robust host capable of growing on a range of lignin-derived monomers as well as on complex depolymerized lignins. One aromatic monomer generated during lignin depolymerization is catechol, which can be converted into the higher-value product muconic acid (MA) in a single enzymatic step. To channel catechol toward MA, a muconate cycloisomerase I deletion mutant was generated and evaluated in small-scale cultivations. MA production was further enhanced through the implementation of improved feeding strategies. Finally, fed-batch fermentation in a 1.2 L bioreactor showed efficient catechol conversion and production of 23 g L^-1 MA. These findings position A. pullulans as a strong platform organism for sustainable lignin valorization and MA production.