Production of natural colorants by metabolically engineered microorganisms

The market demand and customer preference toward natural colorants are rapidly increasing for better environment and health. Systems metabolic engineering allows development of microbial cell factories capable of efficiently producing natural colorants from renewable resources. Metabolic engineering strategies, including flux and pathway optimization, high-throughput screening, substrate channeling, enzyme/membrane/lipid engineering, and process optimization, are employed for developing strains producing natural colorants. Combinatorial expression of pathway genes, the use of promiscuous enzymes, and directed evolution of key enzymes enable production of diversified natural colorants with enhanced properties. Advances in tools and strategies of enzyme discovery and engineering will contribute to the production of diverse natural colorants and their derivatives. Synthetic colorants have predominated over natural colorants mainly due to their relatively more stable color, larger synthesis scale, and lower manufacturing costs. However, the environmental and health impacts arising from the excess use of these chemicals have brought up increasing demand for natural colorants. Recent advances in microbial metabolic engineering are enabling an increasing number of natural colorants to be manufactured at large scale in a greener and sustainable manner. In this paper, we review the metabolic engineering tools and strategies employed for the microbial production of natural colorants and their derivatives, focusing on the enhanced production of major natural colorants and diversification of natural colorants with more desirable physicochemical properties. Future prospects and challenges are also discussed. Synthetic colorants have predominated over natural colorants mainly due to their relatively more stable color, larger synthesis scale, and lower manufacturing costs. However, the environmental and health impacts arising from the excess use of these chemicals have brought up increasing demand for natural colorants. Recent advances in microbial metabolic engineering are enabling an increasing number of natural colorants to be manufactured at large scale in a greener and sustainable manner. In this paper, we review the metabolic engineering tools and strategies employed for the microbial production of natural colorants and their derivatives, focusing on the enhanced production of major natural colorants and diversification of natural colorants with more desirable physicochemical properties. Future prospects and challenges are also discussed. a clustered group of multiple genes that are together involved in a specific biosynthetic pathway of a secondary metabolite. a fermentation strategy to produce a desired compound by culturing multiple microbial strains, sometimes each harboring different portions of the biosynthetic pathways. an RNA-guided gene expression knockdown tool that employs the catalytically dead Cas9 (dCas9) protein to inhibit target gene transcription. a process of performing multiple rounds of mutation and screening to isolate enzymes with desired activity or characteristics. an in silico technique to predict the best matching binding mode of a ligand to a protein. a strategy to predict the structure of a query protein using the already reported crystal structure of a template protein, which shows high sequence similarity to the query protein. intracellular globular membranous structures formed by the protrusion of bacterial inner membrane layer. colorants derived from natural resources. extracellular globular membranous structures formed by the protrusion of bacterial outer membrane layer, which can also be secreted to the culture medium. enzymes that have the activities to catalyze other reactions beyond its main one. a strategy employed to efficiently streamline the metabolic flux from a substrate to a product while minimizing the accumulation of intermediates. a cross-coupling Pd-catalyzed organic reaction where the coupling partners are a boronic acid and an organohalide for the creation of carbon-carbon bonds. artificially synthesized chemicals exhibiting colors, often produced from petroleum-based chemicals. a target gene knockdown tool employing a target-specific noncoding small RNA and a Hfq protein that together block translation of the target gene. an integrative field of study that integrates systems biology, synthetic biology, and evolutionary engineering with the traditional metabolic engineering. enzymes that are used to attach functional groups to target chemicals.