Blue Bacterial Pigment Boosted 2.3-Fold Shows Diabetes and Obesity Potential

A vivid blue pigment made by bacteria is stepping out of the laboratory and into the spotlight as one of the most versatile natural colorants yet described. In a new study published in MicrobiologyOpen, researchers report that indigoidine, a non-ribosomal peptide pigment produced by a nonpathogenic recombinant strain of Escherichia coli BL21-DE3, can be overproduced sustainably through careful fermentation engineering, and that the purified pigment does far more than add color. According to the study, indigoidine strongly inhibits two digestive enzymes central to obesity and type 2 diabetes, activates the AMPK and AKT signaling pathways that govern glucose and energy metabolism, and does so with remarkably low toxicity toward human cells.

The drive to replace synthetic dyes has never been more urgent. Common artificial colorants such as Allura Red, Tartrazine, Sunset Yellow, and Ponceau have been linked in various studies to oxidative damage in multiple organs, systemic inflammation, immune suppression, reduced male fertility, and allergic reactions affecting the skin, respiratory tract, and digestive system, particularly in children. Their environmental footprint is equally troubling: the same chemical stability that makes synthetic dyes attractive to manufacturers makes them poorly biodegradable, allowing them to persist and accumulate in water, soil, plants, and animals, with transformation products that may be toxic or potentially carcinogenic. Natural pigments from microalgae, lichens, plants, and bacteria have emerged as safer alternatives, and bacterial pigments in particular combine renewability, biocompatibility, and documented bioactivities ranging from antioxidant to anti-inflammatory and antimicrobial effects.

Indigoidine has long intrigued scientists because of its striking blue hue and its pharmacological promise, but producing it at industrially meaningful yields has been a persistent bottleneck. The new work began with a systematic comparison of culture media, screening Nutrient Broth, Tryptic Soy Broth, Peptone Glycerol Broth, and Luria-Bertani (LB) medium. Although Peptone Glycerol Broth supported the fastest bacterial growth, standard LB medium proved the most productive for pigment synthesis, yielding 75.8 milligrams of indigoidine per liter per 24 hours. The researchers then applied a two-stage statistical optimization strategy, first using a Plackett-Burman mixture design to identify the most influential nutritional and physicochemical variables, and then refining the three dominant factors with a central composite design implemented in Minitab software.

The results of that optimization were dramatic. Raising tryptone to 1.52 percent and yeast extract to 0.81 percent, introducing glucose at about 1 percent along with l-glutamine, magnesium sulfate, and potassium phosphate, and adjusting the culture to pH 7.8, 29 degrees Celsius, and 200 rpm agitation lifted indigoidine output to 177.4 milligrams per liter per 24 hours, a 2.34-fold increase over the standard medium. The response surface model predicted a maximum near 180 milligrams per liter, and the experimental value landed almost exactly on target, validating the statistical approach. The authors attribute the gains to a richer supply of amino acid and peptide precursors, improved ATP and cofactor availability, better oxygen transfer from increased agitation, and the metabolic support provided by magnesium and phosphate ions. Molecular oxygen is especially critical because it reoxidizes flavin mononucleotide during the enzymatic step catalyzed by the pigment-synthesizing enzyme BpsA.

Purification and characterization confirmed the quality of the product. Following ultrasonic disruption of the bacterial cells and a series of centrifugation and filtration steps, the pigment was recovered as a lyophilized powder with a purity of 92.3 percent, verified by LC-MS and by UV-visible spectroscopy showing the characteristic absorbance maximum at 612 nanometers. Stability testing then mapped how the pigment behaves under food-processing conditions. Indigoidine was most stable near neutral pH, with a half-life of about 150 hours at pH 7.8, but degraded rapidly at extremes, dropping to half-lives of just 3 hours at pH 1 and 10 hours at pH 12. Temperature told a similar story: the pigment endured for 240 hours at 4 degrees Celsius but lost half its content within 2 hours at 100 degrees Celsius. Darkness preserved it best, with a 220-hour half-life, while ultraviolet exposure cut that figure to 20 hours. These findings suggest that indigoidine is well suited to neutral-pH, refrigerated, light-protected applications.

Safety and bioavailability assessments added further credibility to the pigment’s industrial prospects. In a hemolysis assay using freshly isolated human erythrocytes, indigoidine caused less than 2 percent hemolysis at concentrations between 0.5 and 10 micrograms per milliliter, and even at the highest tested dose of 50 micrograms per milliliter hemolysis reached only 5.29 percent, within the generally accepted nontoxic threshold. A membrane distribution experiment showed that the pigment readily penetrates human cell membranes: at low concentrations more than 87 percent of the indigoidine was found inside the erythrocytes, indicating efficient cellular uptake, a property that could allow the molecule to reach intracellular targets in food and pharmaceutical contexts.

The most striking results, however, concerned metabolism. In what the study describes as a first, indigoidine was tested against key enzymes implicated in obesity and diabetes. The pigment inhibited alpha-amylase, the enzyme that breaks down starch and drives postprandial glucose spikes, with an IC50 of 0.69 micrograms per milliliter, close to the 0.36 micrograms per milliliter of the clinical drug acarbose. Molecular docking supported the finding, with a binding energy of minus 7.4 kilocalories per mole versus minus 7.7 for acarbose, and hydrogen bonds to ASP197, ASP300, and GLN63 plus pi-pi interactions with TRP59 stabilizing the complex. Against pancreatic lipase, the fat-digesting enzyme targeted by the anti-obesity drug orlistat, indigoidine actually outperformed the reference compound, achieving an IC50 of 0.37 micrograms per milliliter compared with 0.62 for orlistat, and a stronger docking score of minus 8.1 versus minus 6.9 kilocalories per mole.

Beyond blocking digestion, indigoidine activated the two master switches of cellular energy handling. AMPK, the cellular fuel gauge and a major therapeutic target for diabetes and insulin resistance, was stimulated in a dose-dependent manner up to 65.1 percent activation, with an EC50 of 1.36 micrograms per milliliter, near the 0.98 micrograms per milliliter of the reference activator A-769662. AKT, or protein kinase B, the linchpin of insulin signaling, glucose transport, and glycogen synthesis, was activated up to 65.6 percent with an EC50 of 4.59 micrograms per milliliter and a docking affinity almost identical to that of the standard activator SC79. To test these effects in a living, highly metabolic human cell system, the researchers exposed spermatozoa to the pigment. Glucose consumption rose to 133.4 percent of control at 20 micrograms per milliliter, AMPK activity peaked at 128.9 percent, and AKT activity reached 121.4 percent, all while showing less toxicity at high doses than either A-769662 or SC79, which suppressed metabolism sharply at elevated concentrations.

The convergence of enzyme inhibition, signaling activation, membrane penetration, and low hemotoxicity positions indigoidine as a rare multitarget natural compound, one that could serve simultaneously as a food colorant and a functional bioactive ingredient. The authors caution, however, that several hurdles remain before the pigment can move toward therapeutic use. In vivo studies are needed to confirm the metabolic effects observed in vitro, comprehensive toxicity and safety evaluations must be completed, pharmacokinetics and bioavailability in the body remain uncharacterized, and the precise molecular mechanisms of AMPK and AKT modulation require deeper investigation. Formulation optimization and scale-up of production will also be essential for any commercial application.

Even with those caveats, the study marks a significant advance on two fronts at once. It demonstrates that rational, statistics-guided fermentation can more than double the yield of a bacterial pigment without genetic manipulation of the production strain, and it reveals that the same molecule coloring our foods may also help regulate the digestive enzymes and metabolic pathways implicated in two of the world’s most widespread chronic diseases. As pressure mounts to phase out synthetic dyes and to find gentler, multifunctional alternatives, the deep blue chemistry of indigoidine may prove to be one of microbiology’s most colorful contributions to human health.

Subject of Research: Sustainable fermentation overproduction of the bacterial pigment indigoidine and its inhibitory and activating effects on enzymes involved in obesity, diabetes, and insulin signaling

Article Title: Sustainable Overproduction of the Bacterial Pigment Indigoidine as a Natural Colorant: Stability Evaluation, Inhibition of Obesity‐Diabetes‐Related Digestive Enzymes, and Activation of AMPK–AKT

Article References: Sustainable Overproduction of the Bacterial Pigment Indigoidine as a Natural Colorant: Stability Evaluation, Inhibition of Obesity‐Diabetes‐Related Digestive Enzymes, and Activation of AMPK–AKT. (n.d.). https://doi.org/10.1002/mbo3.70429

Image Credits: AI Generated

DOI: 10.1002/mbo3.70429

Keywords: indigoidine, bacterial pigment, natural colorant, fermentation optimization, alpha-amylase inhibition, pancreatic lipase, AMPK activation, AKT signaling, type 2 diabetes, obesity, Escherichia coli, food safety