Second-Generation Polyhydroxybutyrate Production From Pretreated Corn Lignocellulosic Fraction as a Strategy to Repurpose by Products From the Corn-Processing Chain.

Lignocellulosic residues are non-cost, non-edible, renewable feedstocks that can be used in polyhydroxybutyrate (PHB) production. PHB is a bioplastic synthetized by microorganisms, formed intracellularly under stressful growth conditions; however, its production costs are high, representing the major drawback for fossil-based plastics replacement. The use of lignocellulosic waste in PHB production can help to reduce its costs. Therefore, this work aimed to optimize the second-generation (2G) PHB production process from the lignocellulosic corn fraction (LCF). The LCF is a lignocellulosic by-product generated during first-generation (1G) PHB production from milled corn (Zea mays). A novel integrated citric acid pretreatment followed by enzymatic hydrolysis in just one-pot was employed. Two cellulolytic enzymes from a highly productive strain were employed at an enzyme loading of 11.64 mg β-glucosidase/g substrate and 0.6 mg cellulase/g substrate. These enzymes concentrations were employed in a hydrolysis assay in an agitated tank, reaching 47.37 g/L of total sugars (95.71% of glucose). This hydrolysate was employed as a low-cost carbon source for 2G PHB production by Cupriavidus necator LPB2327. In the optimized condition, 8.90 g/L of dry cell weight (DCW), and 7.64 g PHB/L (85.89% PHB accumulation) were achieved. Overall, high product yields of 0.254 g PHB/g substrate, and 0.127 g PHB/g LCF were obtained. These results indicate the feasibility of using this integrated approach for 2G PHB production within a corn biorefinery strategy.