Achieving high productivity of 2-pyrone-4,6-dicarboxylic acid from aqueous aromatic streams with Novosphingobium aromaticivorans†

Enhancing the production of biochemicals from lignocellulosic biomass is one potential way to decrease society's dependence on fossil fuels. Aromatic compounds obtained from plant biomass can be used as substrates for microbial production of dicarboxylic acids such as 2-pyrone-4,6-dicarboxylic acid (PDC) and cis,cis-muconic acid, which are building blocks for the manufacturing of polymer-based fibers and materials. In this study, we used an engineered strain of the bacterium Novosphingobium aromaticivorans to investigate how to increase PDC productivity in flow-through bioreactors receiving aqueous solutions of aromatics. At the best operational conditions tested, we achieved stable PDC production rates of 0.77 g_PDC L⁻¹ h⁻¹ with p-hydroxybenzoic acid, 1.93 g_PDC L⁻¹ h⁻¹ with syringic acid, and 1.53 g_PDC L⁻¹ h⁻¹ with the products from alkaline pretreated poplar biomass. PDC titers in these reactors ranged from 7.7 to 15 g L⁻¹ (42 to 80 mM) and were limited by aromatic solubility in the case of syringic acid, or by accumulation of protocatechuic acid from p-hydroxybenzoic acid when high aromatic loading rates were used. The use of high aromatic loading rates, hollow-fiber membranes to concentrate the microbial cells, and NH₄OH for pH control were factors that contributed to this study achieving the highest PDC productivities reported to date. Overall, our findings demonstrate strategies that can be used to increase bioreactor productivity when aromatic substrates are delivered in aqueous form. These findings may also provide useful insight for production of other biochemicals from aromatic streams using N. aromaticivorans or other microbial chassis.