Lignin valorization into vanillin: Paving the way for a sustainable aromatic bioeconomy

Lignin is the most abundant renewable aromatic resource on earth. The bioconversion of lignin into aromatic fine chemicals like vanillin aligns with the principles of sustainable “aromatic bioeconomy” concept. However, its recalcitrance and inherent heterogeneity pose significant challenges to efficient biological valorization. Therefore, this review provides a multidisciplinary perspective on aromatic ring-preserving, atom-economical pathways, emphasizing cutting-edge microbial strategies that bridge lignin-derived aromatics to vanillin production without sacrificing aromaticity. Depolymerization strategies are pivotal for enhancing the bioavailability of lignin derivatives, enabling their effective utilization as substrates for downstream vanillin biosynthesis. Furthermore, the design of robust microbial cell factories and the precise regulation of metabolic pathways increase the performance of vanillin biosynthesis. Additionally, advanced fermentation strategies are essential to alleviate vanillin cytotoxicity and enable high-titer production. Furthermore, techno-economic analysis was integrated to benchmark the industrial viability of lignin-based routes. Overall, continued advances in engineering strategies, from lignin depolymerization to vanillin biosynthesis, are reshaping lignin valorization paradigms and driving the development of a sustainable aromatic bioeconomy grounded in aromatic ring conservation.