A room wall whose color does not fade – an international research team has come a step closer to this goal. The subject of their research was colored bacterial cultures. The principle behind it is identical to how butterflies present their colors: These are not created by absorbing certain wavelengths, as in conventional pigments, but by refraction of light. Nanoscopic particles create an optical interference that appears colored to our eyes.
It has long been known that some bacterial colonies also produce such glittering and shimmering structural colors. An example can be seen above: The marine bacterium Marinobacter alginolytica produces ordered structures in its cells that act like a photonic crystal. Their wavelength-specific light refraction creates the shimmering color impression.
To find out how these are produced and what genetic instructions lie behind them, Aldert Zomer from the University of Utrecht and his colleagues analyzed the DNA of 87 colored and 30 colorless bacterial strains. In addition, the international research team trained an artificial intelligence to use the respective genome to determine whether a particular bacterium will develop a color and which one. “With this model, we analyzed over 250,000 bacterial genomes and 14,000 environmental samples from international open science repositories,” explains senior author Bas Dutilh from the University of Jena.
The genetic analyses showed that bacteria from oceans, freshwater areas and the deep sea exhibit a strikingly high frequency of the gene combinations responsible for structural colours. “In contrast, microbes in host-associated habitats, such as the human microbiome, exhibit very little structural colour,” reports Dulith.
But what use is a color that only becomes visible when exposed to light to the bacteria in the pitch-black depths of the sea? The researchers assume that the gene sequences also perform other functions in the organism, such as protecting the bacteria from viruses. In this case, the coloring would just be a nice side effect. A side effect that humans could take advantage of: Sustainable colors that do not contain toxic heavy metals such as chromium and still fade slowly would be one possibility.