The work published by the KAIST Sang Yup Lee group on November 12, 2025, in Trends in Biotechnology (formal issue March 2026; Vol. 44, No. 3, pp. 766-791; DOI 10.1016/j.tibtech.2025.09.019), titled "One-pot production of colored bacterial cellulose." The core innovation is compressing two steps — "spinning" and "coloring" — into a single fermentation vessel, so that when the material grows out, it is already colored, functional, and alive.
🦠What Each of the Two Bacterial Strains Does in the Reactor
- Komagataeibacter xylinus (formerly Gluconacetobacter xylinus) : Feeds on glucose/glycerol/carbon sources. The membrane-bound cellulose synthase polymerizes glucose into β-1,4 nanofibers, which crosslink and self-assemble into bacterial cellulose (BC) membranes/sheets. BC itself is pure white, high-strength, high water-holding capacity, biodegradable, and has long been considered a candidate alternative substrate for petroleum-based polyester/nylon.
- Engineered E. coli : Rather than "extract-then-dye," this strain re-routes natural pigment pathways inside the cell:
- Violacein family (violacein and its derivatives deoxyviolacein, proviolacein, prodeoxyviolacein) covers the green-blue-navy-purple cool-toned spectrum;
- Carotenoid pathways (astaxanthin, β-carotene, zeaxanthin) cover the red-orange-yellow warm-toned spectrum.
The key lies in in-situ color locking: the pigment-producing E. coli secretes pigments extracellularly (via membrane vesicle engineering to relieve intracellular toxicity from pigment accumulation). As the BC fiber network grows, these pigments are physically entrapped and anchored via hydrogen bonding/hydrophobic interactions into the three-dimensional pores. The color is not surface adsorption but co-precipitation with the fibers during growth. Consequently, subsequent tests for wash-fastness, acid/alkali resistance, and high-temperature steam sterilization show no fading — violacein-series color fastness even exceeds some synthetic dyes.
⚗️How "One-Step Growth" Is Coordinated
Direct mixed culture initially failed: the two strains inhibited each other, resulting in either no BC production or no color. KAIST's solution was temporal segregation by color family:
- Cool tones (purple/blue/green) : Let K. xylinus run for 48 hours to build the fiber network first, then introduce violacein-producing E. coli (delayed co-culture). Pigments are secreted and entrapped synchronously during BC formation.
- Warm tones (red/orange/yellow) : Grow pure BC sheets first, then immerse them in carotenoid-producing E. coli culture broth (sequential culture). Color is adsorbed and fixed through the porous structure.
- Fed-batch fermentation scaled up to 6.6 L reactors confirmed: violacein titer reached 8.09 g/L, deoxyviolacein reached 16.92 g/L — both the highest reported in literature at the time. The entire process takes approximately 13 days to produce a full set of seven-colored BC sheets from one pot.
Therefore, "one-step growth from CO₂/sugar" means precisely: carbon source (sugar; long-term vision can interface with CO₂-fixing chassis) → same fermentation system → material + color + functional molecule produced simultaneously, skipping the entire petroleum-based dyeing-and-finishing chain of "spinning → desizing → dyeing → washing → fixing."
🪅Why It Is Being "Re-evaluated by the Natural Pigment Community"
Historically, the natural pigment narrative was about replacing synthetic dyes: extracting indigo, carmine, carotenoids from plants/microbes, then applying them to cotton/silk/polyester. This still requires water, auxiliaries, and wastewater treatment — fundamentally an "extract-apply-fix" paradigm. KAIST's approach shifts the boundary:
- Pigments do not need to be extracted and never contact the fabric; they are born on-site during material synthesis;
- The material is not a textile carrier but a "grown living material" where color, antibacterial properties, and porous structure are co-products of a single fermentation;
- Violacein itself possesses broad-spectrum antibacterial, anti-biofilm, and moderate antioxidant activity. When embedded into BC — which already has high water retention and an extracellular-matrix-like structure — the combination directly yields a self-colored antibacterial wound dressing without requiring post-loading of silver ions or antibiotics.
This is exactly what it's meant by "being reclassified as a grown material rather than a pigment substitute" — it competes for the market share of medical dressings, wearable bioelectronic substrates, and packaging films, not for competing with disperse dyes in garment dye baths.
⚕️Logic for Spillover into Medical Dressings
Bacterial cellulose as a dressing material is already a mature direction (high water retention, conformable to wounds, drug-loadable, with established ISO 10993/FDA 510(k) pathways). Adding violacein-series in-situ coloring brings three additional layers of value:
- Antimicrobial property as structural attribute: Active against S. aureus and P. aeruginosa, eliminating the need for additional drugs in chronic ulcers/burn wounds;
- Color as indicator function: Violacein exhibits significant color shifts under different pH/oxidation states, enabling visual wound pH monitoring;
- No synthetic dye leaching: Avoids the toxicological assessment burden associated with traditional dyed dressings (e.g., iodine-loaded, methylene blue-loaded).
Current bottlenecks remain straightforward: the 13-day cycle is too long; substrate competition between the two strains during scale-up; BC sheets require further processing into nonwoven/fiber form; cost cannot yet compete with petroleum-based polyester (Lee himself estimates commercialization is at least 5 years away). However, medical dressings, high-end biodegradable packaging, and other small-area, high-value-added, green-premium-tolerant scenarios will achieve commercial landing before apparel.
