Recent Advances on Natural Pigment Indigoidine: Occurrence, Biosynthetic Approaches, and Applications.

Indigoidine, a natural biopigment with a planar conjugated structure comprising two pyrrolidinone rings linked by a central double bond, exhibits unique chromogenic properties. Growing environmental concerns over synthetic and plant-derived pigments have driven interest in microbial pigments as sustainable alternatives. Despite the potential of nonribosomal peptide synthetases (NRPSs) to optimize indigoidine biosynthesis, mechanistic insights into their catalytic functions remain limited. This review systematically outlines the discovery and evolution of indigoidine, focusing on the structural features of NRPSs and associated biosynthetic pathways. It evaluates current strategies for enhancing production, including host engineering, metabolic flux optimization, genome-wide screening, transcriptional regulation, and scale-up processes. Additionally, the applications of indigoidine in textile, agricultural, and biomedical industries are critically examined. By proposing a novel research framework for microbial pigments synthesis optimization, this review contributes theoretical and technical advancements toward sustainable biopigment manufacturing.