Iridescent Colonies of Bacteria

[Recusant]

"Get your act together you microbes, it's showtime!" The scientists understand the how of it, but why the show? According to the article they don't know, but they have a few hypotheses. 

"We Finally Know How Bacteria Shimmer in Brilliant Colors Without Pigment" | Science Alert

[Sparing you the garish GIF you'll find at the article . . .]

When the marine bacteria Marinobacter alginolytica gather into colonies they form
photonic crystal shapes that can produce color through interference effects.
Image credit: Colin Ingham.

From shifting skink rainbows to dazzling hummingbird metallics, many creatures display brilliant hues created by nano-structures weaving wavelengths of light.

Researchers led by Utrecht University bioinformatician Aldert Zomer have now pinpointed genes that allow bacteria to make use of this vivid phenomenon too.

Where colors emitted by pigments are the leftover parts of the visible light spectrum that aren't absorbed, structural colors arise from the way light interferes as it is reflected.

The projected colors depend on how small-scale structures on the surface of a material direct light, causing some wavelengths to combine or cancel. What a viewer sees can shift according to their viewing angle, causing dramatic changes in color intensity or iridescent color transitions.

Individual microbes, such as the marine bacterium Marinobacter alginolytica, can act as nanostructures, coordinating with each other to form colonies in a precise pattern that allows them to reflect specific wavelengths.

[. . .]

Surprisingly, structural color even appeared in bacteria that live where there's no light to reflect.

"We discovered that the genes responsible for structural color are mainly found in oceans, freshwater, and special habitats such as intertidal zones and deep-sea areas," explains University of Jena viral ecologist Bas Dutilh. "In contrast, microbes in host-associated habitats such as the human microbiome displayed very limited structural color."

That structural color appears in the ocean's depths suggests the nanostructures involved likely serve biological processes other than dazzling observers. For example, they may act as defensive structures against viruses or help the cells latch onto floating food particles, the researchers explain.

Or structural color in bacteria may even have arisen merely as a side effect of how bacteria organize themselves into their colonies.

Understanding how nature creates structural colors could allow us to develop environmentally friendly materials with enduring colors and other desirable properties like light weight paint for planes.

[Link to full article.]

The paper is open access:

"Structural color in the bacterial domain: The ecogenomics of a 2-dimensional optical phenotype" | PNAS

Abstract:

Structural color is an optical phenomenon resulting from light interacting with nanostructured materials. Although structural color (SC) is widespread in the tree of life, the underlying genetics and genomics are not well understood.

Here, we collected and sequenced a set of 87 structurally colored bacterial isolates and 30 related strains lacking SC. Optical analysis of colonies indicated that diverse bacteria from at least two different phyla (Bacteroidetes and Proteobacteria) can create two-dimensional packing of cells capable of producing SC.

A pan-genome-wide association approach was used to identify genes associated with SC. The biosynthesis of uroporphyrin and pterins, as well as carbohydrate utilization and metabolism, was found to be involved. Using this information, we constructed a classifier to predict SC directly from bacterial genome sequences and validated it by cultivating and scoring 100 strains that were not part of the training set. We predicted that SCr is widely distributed within gram-negative bacteria.

Analysis of over 13,000 assembled metagenomes suggested that SC is nearly absent from most habitats associated with multicellular organisms except macroalgae and is abundant in marine waters and surface/air interfaces. This work provides a large-scale ecogenomics view of SC in bacteria and identifies microbial pathways and evolutionary relationships that underlie this optical phenomenon.

[Tank]

Fascinating

[Asmodean]

Cool!

Yes, the whys sound rather on the speculative side of things, but I suspect that sort of color production may indeed be a byproduct of something else them bacteria find useful.