Living bacteria embedded in silicone can absorb green LED light and re-emit it as red, offering a potential sustainable alternative to rare-earth phosphors in lighting.
(Nanowerk Spotlight) Imagine a future where the color of light in your home comes not from rare metals mined from the earth, but from living bacteria genetically programmed to fluoresce.
The idea builds on decades of work with fluorescent proteins, molecules that absorb light at one wavelength and re-emit it at another. Scientists first extracted one such protein from the crystal jellyfish Aequorea victoria in the 1960s, but the real breakthrough came in the 1990s when researchers learned to clone the gene and express it in other organisms. That work eventually earned the 2008 Nobel Prize in Chemistry and revolutionized cell biology by giving scientists a way to tag and track molecules inside living cells.
The idea of harnessing these proteins for practical lighting has attracted engineers ever since. A biological color converter could, in principle, be biodegradable and free from toxic materials. But the gap between a glowing protein in a laboratory dish and a functional lighting component remains wide.
One promising approach focuses not on replacing LEDs, but on improving the filters that sit atop them. Modern light-emitting diodes are remarkably efficient, but they typically produce blue or green light. To create the warm white glow that consumers prefer, manufacturers coat LED chips with phosphors, materials that absorb high-energy photons and re-emit lower-energy light in reds, yellows, and greens.
The problem is that most commercial phosphors rely on cerium-doped yttrium aluminum garnet, a rare-earth material requiring energy-intensive mining. Some manufacturers use cadmium-based quantum dots, which offer excellent color quality but raise toxicity concerns. Policy roadmaps in the European Union and the United States emphasize the need for sustainable alternatives by 2030.
Could bacteria producing fluorescent proteins serve as biological phosphors? The concept builds on work demonstrating that single cells can function as gain media in biological lasers and as intracellular sensors. Yet translating these findings into practical devices has stumbled on a fundamental problem.
The workhorse bacterium of molecular biology, Escherichia coli, does not survive well when embedded in polymer coatings. The cells aggregate into visible clumps, scatter light, and often lose viability, releasing their contents and destroying the fluorescence that makes them useful.
A research team based at the Technical University of Munich has now demonstrated a more practical approach. In a paper published in Advanced Materials (“Integrating Vibrio natriegens for Photon Manipulation in Living Lighting Devices”), the scientists report that Vibrio natriegens, a marine bacterium famous for its extraordinary growth rate, can be genetically engineered to produce red fluorescent protein and embedded directly into a silicone matrix without extensive preprocessing. The resulting filters, placed atop conventional green LEDs, powered the first red-emitting bacterial hybrid lighting devices.
Under direct operation, color stability lasted several days; under optimized low-temperature, remote configurations, it extended to two weeks.
Screening of cultivation conditions in independent triplicates with respect to the changes of the ϕ of DsRed pelleted cells using cultivation times of (A) 48 h and (B) 24 h at different temperatures. The comparison was done in baffled and non-baffled flasks. (C) Picture of a V. natriegens cell culture after optimizing cultivation temperature and incubation time. (D) Absorbance (E) emission (solid line; λex = 280 nm) and excitation (dashed line; λem = 630 nm) spectra of purified DsRed produced by E. coli and V. natriegens (n = 3 batches). (F) Emission (solid line; λex = 450 nm) and excitation (dashed line; λem = 640 nm) spectra of purified DsRed (orange) and V. natriegens cells expressing DsRed in suspension (grey). (Image: reproduced from DOI:10.1002/adma.202514435, CC BY) (click on image to enlarge)
The choice of V. natriegens reflects a calculated bet on the organism’s unusual biology. This salt-loving bacterium boasts the fastest doubling time of any established platform for producing foreign proteins, replicating in less than 10 minutes under ideal conditions. Its metabolic flexibility allows it to use a wide variety of carbon and energy sources.
Perhaps most importantly, V. natriegens produces sugar-based protective coatings around its cells and possesses a membrane adapted to high-salt environments. The researchers hypothesized that these features might help the bacteria survive encapsulation in water-repelling materials that would kill ordinary E. coli.
The team engineered V. natriegens to express DsRed, a red fluorescent protein originally derived from coral. After optimizing cultivation conditions, they found that incubating the bacteria at 25 °C for 24 hours yielded the best results. At this temperature, the protein folded correctly and its light-absorbing chemical core matured properly.
Higher temperatures led to misfolding and lower quantum yields, a metric describing how efficiently absorbed light converts into emitted light. At 37 °C, quantum yields dropped to just 23 %, while 25 °C produced values around 58 % to 60 %.
Comparing engineered V. natriegens with E. coli producing the same protein, the researchers found similar final concentrations of purified DsRed: approximately 119 mg L⁻¹ for E. coli and 102 mg L⁻¹ for V. natriegens. The crucial difference lay in volumetric productivity, which measures how quickly bacteria generate the target protein. V. natriegens achieved 4.25 mg L⁻¹ h⁻¹, a 1.7-fold improvement over E. coli’s 2.48 mg L⁻¹ h⁻¹.
With protein production optimized, the team turned to embedding the bacteria in silicone. When E. coli cells were mixed into the material, they formed large aggregates unsuitable for device fabrication. V. natriegens, by contrast, dispersed into small, homogeneous clusters that appeared uniform to the naked eye.
Crucially, the bacteria remained alive inside the silicone. The researchers demonstrated this by placing fresh coatings into liquid growth medium and inducing protein expression. The bacteria resumed growing and producing fluorescent protein. This means the filters are not merely biodegradable but potentially renewable: spent coatings could, in principle, be recultivated to yield fresh bacteria for new devices. Silicone-embedded cells retained quantum yields of approximately 58 %, essentially unchanged from cell pellets before encapsulation.
The team fabricated hemisphere-shaped filters and placed them onto commercial 520 nm green LEDs. These devices achieved photon down-conversion efficiency exceeding 95 %, converting most green light into red emission centered at 590 nm. Luminance values reached approximately 35,000 cd m⁻² at 200 mA.
Device stability depended strongly on temperature. At 28 °C, devices maintained stable output for roughly 72 hours before losing half their initial intensity. At 37 °C, that figure dropped to about 18 hours. In a remote configuration operating below 25 °C, with the filter positioned 2 cm from the LED, color stability persisted for 14 days.
Separate thermal experiments confirmed that temperature, rather than light exposure, posed the primary threat to longevity. Filters incubated at 44 °C lost half their fluorescence within 2 hours; those held at 31 °C survived roughly 8 hours.
This work represents a conceptual shift. Previous efforts using E. coli required converting bacteria into spheroplasts, cells with outer walls partially removed, and embedding them in water-absorbing polymers. That process demanded additives and multiple steps. The V. natriegens approach allows untreated bacteria to mix directly into industrially relevant silicone.
Significant challenges remain. The narrow temperature window limits practical applications. The team acknowledges the need for strains with improved thermal tolerance and for life-cycle analyses to assess true sustainability benefits.
Nevertheless, this research establishes V. natriegens as a promising platform for living optoelectronics. The bacterium’s combination of rapid growth, efficient protein production, compatibility with hydrophobic materials, and recultivability opens possibilities for sustainable lighting, bio-imaging, and photovoltaics. Bacteria serving as color converters in household lighting still sounds improbable, but it has moved measurably closer to reality.
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