Inspiration

Our project was inspired by a goose with feathers dyed unnatural blue (Figure 1). This scene, beautiful at first glance yet disturbing upon reflection, turned out to be the result of textile dye pollution in the water. The picture shocked us and revealed the hidden cost of the fashion industry. It made us realize how chemical dyes, though common in textiles, can cause severe and irreversible damage to ecosystems. This moment of discovery prompted us to reflect on the textile industry and motivated us to search for a sustainable alternative.

Figure 1. The chemically-dyed blue goose feathers (Photo credit: AP Photo/Andre Penner).

Traditional Textile Industry: A Major Source of Pollution

The textile industry is the world's second-largest source of pollution, leaving a substantial ecological footprint^[1].

The fibers used in textile production primarily fall into two categories: synthetic fiber and natural fiber. Among them, approximately 90% of synthetic fibers are derived from petroleum-based sources^[2], with an estimated annual oil consumption of 342 million barrels^[3] . The manufacturing of these fibers is characterized by intensive energy use, high carbon emissions, and extreme resistance to degradation^[4]. Current estimates suggest that the textile sector emits around 2.1 billion metric tons of greenhouse gases each year^[5]. Even more concerning is the fact that synthetic fiber garments contribute to 35% of all microplastics in the ocean ^[6]. With the production of synthetic fibers continuing to rise rapidly, the environmental burden is expected to intensify further in the coming years (Figure 2).

Figure 2. Global population growth and fiber-type-based increase in textile production^[7].

In contrast, while natural fibers are biodegradable, their production and utilization are not without significant ecological costs. Studies show that producing one ton of natural fiber from cotton requires approximately 3,644 cubic meters of water. Moreover, cotton farming accounts for about 25% of global insecticide use and over 10% of pesticide consumption worldwide^[8]. Clearly, both synthetic and natural fibers exact a considerable environmental toll.

The widespread use of synthetic dyes, such as azo dyes which release carcinogenic aromatic amines, is another source of pollution^[9]. Nearly 7 million tons of synthetic dyes are produced globally each year^[10]. Due to their chemical properties, most of these dyes cannot be effectively removed by conventional wastewater treatment processes^[11]. As a result, they are frequently discharged into aquatic environments in their original or transformed forms^[12]. These serious threats to aquatic ecosystems and also endangers human health^[13].

In light of these multifaceted environmental challenges posed by the traditional textile industry, there is an urgent need to explore environmentally friendly alternatives and accelerate the transition toward a green, low-carbon, and sustainable future.

Shortcomings in Current Approaches: Lack of Integration between Bacterial Cellulose Synthesis and Dyeing

Fortunately, we found an ideal material to replace traditional textile fibers, namely bacterial cellulose. Because of its high purity, nanostructure, high mechanical property, excellent biocompatibility and degradability, bacterial cellulose thus possesses significant advantages in the fields of environmental textiles (Table 1).

Table 1. Comparison of bacterial cellulose and traditional textile materials.

Property	Bacterial Cellulose (BC)	Cotton / Flax (Plant Cellulose)	Polyester (PET)
Origin & purity	Microbial fermentation; high purity[14]	Agriculture; contains lignin & hemicellulose, requires purification[14]	Petroleum-derived, synthetic
Fibril structure	Nanofibers 20–100 nm, highly ordered network[14]	Larger, less homogeneous microfibrils[14]	Continuous polymer chains; no fibrous hierarchy
Mechanical properties	Tensile strength 200–300 MPa; Young's modulus 15–35 GPa[14]	Tensile strength 287–597 MPa; modulus 5–12 GPa[14]	Tensile strength ~55–75 MPa; Young's modulus ~2.8–3.1 GPa[15]
Biocompatibility	Excellent; already applied in wound dressings and scaffolds[14]	Good	Poor, requires finishing
Biodegradability	Fully biodegradable (weeks–months)[14]	Biodegradable (months)	Very poor (hundreds of years)

However, bacterial cellulose produces monochromatic colours, which hinders the promotion of bacterial cellulose in textile and fashion applications^[16].

To promote the development of bacterial cellulose in the fashion industry, researchers have developed a two-step process for dyeing bacterial cellulose based on Acetobacter xylinum. However, the acidic substances produced by the metabolism of Acetobacter xylinum are not suitable for pigment synthesis^{[17, 18]}. Therefore, this process requires the synthesis of bacterial cellulose by Acetobacter xylinum in a specific system at first, and then the obtained cellulose is transferred to an independent dye synthesis system to complete the dyeing process^[19] (Figure 3). It is evident that, in the two-step process, the multi-stage system transfer and independent operations significantly increase energy consumption and time costs; moreover, the step switching and the discharge of reaction waste increase the burden and cost of waste liquid treatment, which is contrary to the concept of "Environmentally Friendly Fashion" advocated by the public.

Figure 3. Schematic diagram of two-step method^[18].

Then, an important question emerges from these challenges: is it possible to integrate the dyeing process with fabric synthesis, enabling microorganisms to create textiles that are both visually appealing and sustainable?

Acetobacter xylinum lacks metabolic pathway diversity and a complete genetic engineering toolkit, and its metabolism acidifies the medium, disrupting pigment synthesis; thus, intrinsic limitations currently hinder integration of cellulose and pigment production. Therefore, Escherichia coli came into our sight. Compared with Acetobacter xylinum, Escherichia coli exhibits rapid growth, high genetic tractability, and broad metabolic versatility (Table 2), which therefore makes it an ideal chassis for integrating bacterial cellulose and pigment production.

Table 2. Comparison of key characteristics of Escherichia coli and Acetobacter xylinum.

Parameter	Escherichia coli	Acetobacter xylinum
Bacterial cellulose yield	~1 g/L (1 day, engineered strain)[20]	Up to 10 g/L (7–14 days)[19]
Dye/pigment synthesis	Competent to produce various pigments (e.g., indoles, anthocyanins)[21]	Not suitable for certain pigments
Ease of genetic manipulation	Well-established tools; easy to manipulate (CRISPR, plasmids, promoter libraries available)	Limited genetic tools; relatively difficult to manipulate
Growth rate	Fast (generation time ~20-30 min)	Slow (generation time >3-4 h)
Carbon source preference	A wide range of carbon sources (e.g., glucose, glycerol)	Glucose, mannitol; narrower range

Our Solution

To handle these problems, NAU-CHINA 2025 established an Escherichia coli–based weaving and dyeing integrated system for one-step synthesis of colored bacterial cellulose via temperature control. This project enabled a customizable and pollution-free dyeing process by expressing natural pigments. Additionally, we covered bacterial cellulose with hydrophobic to form a hydrophobic coating, enhancing the waterproof performance of the fabric. We hoped that such solution would alleviate the current crisis in the fashion industry and promote the coexistence of environmental protection and fashion.

Overview

The complexity of the traditional two-step coloured bacterial cellulose production strategy blocks its further development to a new environmentally friendly fashion alternative^[19]. Therefore, we constructed a temperature-controlled one-pot production platform which consisted of four parts: temperature regulation module, cellulose synthesis module, dyeing module and waterproof module. In the future, we hope to apply our design in industry to promote fashion to a new generation (Figure 4).

Figure 4. The graphic abstract of temperature-controlled one-step synthesis of colored bacterial cellulose in engineered bacteria.

Temperature Regulation Module

To precisely control the whole process, we integrated the thermo-sensitive sensor with our one-pot strategy. Our team placed CI857, a temperature-associated transcriptional regulator derived from bacteriophage λ^[22], under the control of a constitutive promoter P_{BBa_J23119}.

At 25°C, CI857 monomers polymerize to form dimers that bind to the R promoter region, while the FourU RNA thermometer adopts a stem-loop structure^[23], cooperatively preventing the expression of the downstream phlF which encodes PhlF, a TetR-family repressor towards phlF promoter^[22]. The inhibition of the repressor activates the cellulose synthesis process guided by the phlF promoter (Figure 5).

Figure 5. The mechanism of cI857 and FourU^[23] and the gene circuit of the temperature regulation module and its realization at 25°C.

In contrast, at 37°C, with the dissociation of CI857 dimers and the stem-loop structure of FourU^{[22, 23]}, R promoter starts the transcription of phlF, restraining its corresponding promoter^[22], which terminates the cellulose production module and initiates the dyeing part (Figure 6).

Figure 6. The gene circuit of the temperature regulation module and its realization at 37°C.

Cellulose Synthesis Module

We introduced the bacterial cellulose synthase (bcs) operon from Komagataeibacter sucrofermentans to leverage Escherichia coli to produce bacterial cellulose. The operon is primarily comprised of 4 genes: bcsA, bcsB, bcsC and bcsD. After the cellulose biosynthesis regulatory protein BcsB binds to the cyclic di-GMP-positive effector, the main bacterial cellulose synthase enzyme encoded by bcsA incorporates UDP glucose units in the cytoplasm into a 1,4-glucan cellulose chain through periplasm where BcsD crystallizes four glucan chains and at last, BcsC exports the bacterial cellulose micro-fibrils into the extracellular space (Figure 7)^[24].

Figure 7. Genetic organization of bcs operon^[1]
When BcsA (green) is activated by c-di-GMP, it incorporates glucose units into a cellulose chain in the cytoplasm using UDP glucose as a substrate. BcsB (blue) guides the glucan chain through the periplasm; BcsD (orange) crystallizes four glucan chains in the periplasm, and finally, BcsC (gray) exports the BC micro-fibrils into the extracellular space.

To enlarge the production, we introduced a cyclic amplification circuit based on the luxI/luxR quorum sensing system. When the translation of phlF is suppressed, the LuxI enzyme catalyzes the synthesis of acyl-serine lactone (AHL) molecules. The combination of AHL and its receptor protein LuxR renders the efficient expression of the ­lux promoter. As we put another luxI gene after the promoter, more AHL molecules are generated to bind to the LuxR receptor, which realizes the cyclic amplification effect (Figure 8a)^[25]. Thus, a tremendous number of σ factors encoded by ECF11_3726 accumulates inside cells, activating the ecf11_3726 promoter that starts the expression of the bcs gene cluster (Figure 8b)^[26].

Figure 8. Amplifier in bacterial cellulose production.

Dyeing Module

Different colours are necessary for manufacturing clothes and we found two pigments that enable the dyeing of bacterial cellulose: eumelanin and indigo.

As for eumelanin synthesis, tyrosinase1 (TyrBm) from Bacillus megaterium catalyzes the hydroxylation of L-tyrosine to L-DOPA and the conversion from L-DOPA to dopaquinone which is oxidized to eumelanin spontaneously in the presence of oxygen (Figure 9)^[19].

Figure 9. The mechanism of TyrBm that catalyzes the transformation of L-tyrosine to dopaquinone^[19].

With regard to the production of indigo, we employ CYP102A, a kind of cytochrome from Streptomyces cattleya that assists C-5 specific hydroxylation of indole produced by Escherichia coli through tryptophan to 3-hydroxylation with NADPH as coenzyme, resulting in indigo production (Figure 10)^{[27, 28]}.

Figure 10. The mechanism of CYP102A that catalyzes the transformation of indole to 3-hydroxyindole^[28].

Waterproof Module

Besides the colourful appearance, practical functions such as hydrophobicity attach the same importance. Thus, we engineered a biofilm-surface layer protein A with a double cellulose binding module (BslA-dCBM) from Bacillus subtilis to connect the recombinant protein with the cellulose (Figure 11b)^[29]. Once induced by IPTG, T7 promoter starts the expression of bslA-dcbm, hence forming a waterproof coat over our bio-based textiles (Figure 11a).

Figure 11. The implementation and circuit of the waterproof module.
a. The gene circuit of the waterproof module. b. Ideal interaction of BslA-CBMs with BC fibres^[30].

Our project aims to develop an integrated temperature-controlled weaving and dyeing system, which enables bacterial cellulose production and dyeing in one same pot by setting different temperatures. Additionally, we look forward to covering our dyed substrate with recombinant hydrophobic protein coatings to endow the fabric with more functions so as to better adapt to various environments. To sum up, our project is dedicated to providing new solutions to the challenges in bacterial cellulose-based items production in the fashion industry, promoting the commercialization of environmentally textile production. In the future, we anticipate synthesizing more kinds of pigments based on customers' demands and modify the products with abrasive resistance, breathability and other characteristics in order to produce fabrics that combine aesthetic appeal with practicability.

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