Indigo is an ancient dye uniquely capable of producing the signature tones in blue denim; however, the dyeing process requires chemical steps that are environmentally damaging. We describe a sustainable dyeing strategy that not only circumvents the use of toxic reagents for indigo chemical synthesis but also removes the need for a reducing agent for dye solubilization. This strategy utilizes a glucose moiety as a biochemical protecting group to stabilize the reactive indigo precursor indoxyl to form indican, preventing spontaneous oxidation to crystalline indigo during microbial fermentation. Application of a β-glucosidase removes the protecting group from indican, resulting in indigo crystal formation in the cotton fibers. We identified the gene coding for the glucosyltransferase PtUGT1 from the indigo plant Polygonum tinctorium and solved the structure of PtUGT1. Heterologous expression of PtUGT1 in Escherichia coli supported high indican conversion, and biosynthesized indican was used to dye cotton swatches and a garment.

靛蓝是一种古老的染料，能够在蓝色牛仔布上产生标志性色调。然而，染色过程需要对环境造成破坏的化学步骤。我们描述了一种可持续的染色策略，该策略不仅避免了在靛蓝化学合成中使用有毒试剂，而且还消除了对染料溶解还原剂的需求。该策略利用葡萄糖部分作为生化保护基团来稳定反应性靛蓝前体吲哚酚以形成靛蓝，从而防止微生物发酵过程中自发氧化为结晶靛蓝。应用β-葡萄糖苷酶可去除靛蓝的保护基团，从而在棉纤维中形成靛蓝晶体。我们从靛蓝植物蓼中鉴定出编码葡萄糖基转移酶 PtUGT1 的基因，并解析了 PtUGT1 的结构。 PtUGT1 在大肠杆菌中的异源表达支持高印度聚糖转化，生物合成的印度聚糖用于对棉布样本和服装进行染色。