Metabolic engineering of Pseudomonas sp. NGC7 for glucose-free 4-hydroxybenzoic acid production

4-hydroxybenzoate (HBA) is an aromatic component that forms the basis of great number of specialty plastics and fine chemicals. In pursuit of a greener and sustainable production, this article described Pseudomonas sp. NGC7, which has been metabolically engineered for the production of HBA from a mixture of aromatic compounds from sugarcane bagasse fractionated by alkaline treatment. While biomass-derived saccharides will continue to be in use, alternative carbon feedstocks for bioproduction are also desirable. For this reason, our work focused on producing HBA from a complex mixture of aromatics derived from lignocellulosic biomass. Following a mild alkaline treatment of sugarcane bagasse, the extracts principally comprised an aromatic mixture of p-coumarate, ferulate, 4-hydroxybenzaldehyde, HBA, syringaldehyde, syringate, vanillin, and vanillate. An HBA hydroxylase gene (pobA) knockout of NGC7 could produce HBA while utilizing the alkaline extract as a carbon source. The regulator gene (ferR) associated with the degradation pathway of hydroxycinnamate derivatives in NGC7 was identified, and its disruption enhanced the production rate of HBA from the extract. The engineered ⊿pobA⊿ferR strain proliferated and produced >6 g/L HBA with a yield of exceeding 90 mol% efficiently from the alkaline extract in the absence of saccharides. This study proved that "glucose-free HBA production" is attainable through metabolic flux manipulation in NGC7.