The bioconversion of lignin derivative aldehydes into high-value aromatic alcohols and lipids via Lipomyces starkeyi

Lignin carries great potential as an attractive alternative to petroleum-based products. In particular, biological lignin conversion to various value-added products has recently gained attention owing to its promising benefits in supporting the future bioeconomy. The oleaginous yeast Lipomyces starkeyi is a promising organism due to its impressive native abilities to tolerate and metabolize various lignin monomer derivatives and its ability to synthesize single-cell oil (lipids) inside the cells. Herein, we investigated the coupling abilities of lignin monomer metabolism and lipid biosynthesis via L. starkeyi. Three representatives of lignin derivative aldehydes (4-hydroxybenzaldehyde (H-lignin), vanillin (G-lignin), and syringaldehyde (S-lignin)) were converted into their alcohol forms (4-hydroxybenzyl alcohol, vanillyl alcohol, and syringyl alcohol, respectively) without the formation of undesirable byproducts, and each was maintained in its alcohol form for the remaining cultivation. In addition, a double concentration of syringaldehyde in individual lignin fermentation promoted cell growth (17.01 g L-1) and lipid accumulation (30.72% (w w-1)). However, mixed fermentation of all lignin aldehydes resulted in heavy inhibition of the cells. Hence, combination fermentation strategies of high initial inoculum size using a medium with a high C:N ratio were beneficial to improving the fermentation time and lipid titer increment up to 2.6-fold. Overall, this study describes the first prospective of lignin alcohol and lipid production from lignin derivative aldehydes via L. starkeyi.