Gallic Acid Bioproduction: From Tannin Hydrolysis to De Novo Biosynthesis by Engineered Microbial Cell Factories

Gallic acid (GA) is a value-added phenolic compound widely applied in the food, pharmaceutical, and cosmetic industries. Traditionally obtained through chemical hydrolysis of tannins, its production faces limitations related to environmental impact, substrate dependency, and process sustainability. In recent years, microbial platforms have emerged as promising bioproduction alternatives, driven by advances in metabolic engineering and synthetic biology. This review discusses the transition from conventional enzymatic tannin hydrolysis to the engineering of microbial cell factories to enable de novo GA biosynthesis via shikimate pathway reprogramming. This work summarizes reported strategies, including tannase-mediated bioconversion, exploration of native GA-producing microorganisms, and rational pathway reconstruction in model chassis such as Escherichia coli, Corynebacterium glutamicum, and Pseudomonas putida. Emphasis is given to recent approaches involving carbon flux redirection, deletion of competing catabolic routes, enzyme engineering, dynamic regulatory circuits, and tolerance improvement. Current challenges related to metabolic bottlenecks, product toxicity, and industrial scalability are critically analyzed. By integrating enzymatic, metabolic, and systems-level strategies, this review highlights the progress achieved in microbial GA production and outlines perspectives for the development of robust and sustainable biotechnological platforms.