Biorefinery approach for rhamnolipid production by metabolically engineered Pseudomonas taiwanensis VLB120

Abstract

Most biorefinery processes based on lignocellulosic biomass (LCB) focus only on the utilization of sugars hydrolysate from the pre-treated biomass, thus underutilizing or not utilizing lignin. Although there is considerable focus on metabolic engineering for bioconversion of synthetic lignin-related aromatics, it has been far less on using depolymerized lignin as a substrate due to its complex nature. In this work, we demonstrate an integrated biorefinery approach to co-utilize all components of corncob biomass for bioconversion to rhamnolipids by using a metabolically engineered Pseudomonas taiwanensis VL120. Our results show that sequential processes of steam explosion, enzymatic hydrolysis, and base catalysis could result in sugar-rich and lignin-rich streams that can be used for rhamnolipid production. We first show that base-catalyzed depolymerization of lignin-rich fraction of corncob (leftover from the cellulose hydrolysis of pre-treated corncob LCB) results in 5.6 g/L of p-coumarate as the predominant monomer in the aromatic mixture. This was used as a substrate by P. taiwanensis VL120 to achieve 500 mg/L of rhamnolipid. In addition, the sugar-rich hydrolysate obtained from corncob with glucose and xylose as major sugars was used to produce 1.4 g/L rhamnolipids. Further, 650 mg/L rhamnolipid production was achieved from a substrate mixture containing the sugar-rich hydrolysate and p-coumarate-rich depolymerized lignin. This is the first report demonstrating rhamnolipid production in a single-pot fermentation by utilizing all three major monomers from hydrolyzed corncob biomass.