Lipid Production from Dilute Alkali Corn Stover Lignin by Rhodococcus Strains

Biotransformation of lignin to lipids is challenging due to lignin’s recalcitrant nature as a phenolic heteropolymer with a nonuniform structure that imparts rigidity and recalcitrance of plant cell walls. In this study, wild and engineered Rhodococcus strains (R. opacus PD630 and R. jostii RHA1 VanA–) with lignin degradation and/or lipid biosynthesis capacities were selected to establish fundamental understanding of the pathways and functional modules necessary to enable a platform for biological conversion of biomass-derived lignin to lipids. Degradation of lignin (39.6%, dry weight) was achieved by performing cofermentation with wild type R. opacus PD630 and engineered R. jostii RHA1 VanA–. Co-fermentation of these two strains produced higher lipids yield than single strain fermentation. Profiles of metabolites produced by the Rhodococcus strains while growing on alkali technical lignin suggested that lignin was depolymerized to reactive intermediates, such as vanillin, 2,3-dihydro-benzofuran, 2-methoxy-4-vinylphenol, and 3-hydroxy-4-methoxy-benzaldehyde, for lipid biosynthesis. Additionally, fatty acids (C13–C24), especially palmitic acid (C16:0; 35.8%) and oleic acid (C18:1; 47.9%), were accumulated in cells of R. opacus PD630 and R. jostii RHA1 VanA– with lignin as the sole carbon source. Results suggest that the cofermentation strategy can depolymerize lignin into aromatics and promote the lipid production. The lipids produced during cofermentation of lignin by R. opacus PD630 and R. jostii RHA1 VanA– showed promising potential in biofuel production.