Scytonemin is a secondary metabolite and an extracellular matrix (sheath)

pigment A pigment is a colored material that is completely or nearly insoluble in water. In contrast, dyes are typically soluble, at least at some stage in their use. Generally dyes are often organic compounds whereas pigments are often inorganic compo ...

synthesized by many strains of

cyanobacteria Cyanobacteria (), also known as Cyanophyta, are a phylum of gram-negative bacteria that obtain energy via photosynthesis. The name ''cyanobacteria'' refers to their color (), which similarly forms the basis of cyanobacteria's common name, blu ...

, including ''

Nostoc ''Nostoc'', also known as star jelly, troll’s butter, spit of moon, fallen star, witch's butter (not to be confused with the fungi commonly known as witches' butter), and witch’s jelly, is the most common genus of cyanobacteria found in vari ...

'', '' Scytonema'', ''Calothrix'', '' Lyngbya'', ''Rivularia'', '' Chlorogloeopsis'', and ''Hyella''. Scytonemin-synthesizing cyanobacteria often inhabit highly insolated terrestrial, freshwater and coastal environments such as deserts, semideserts, rocks, cliffs, marine intertidal flats, and

hot spring A hot spring, hydrothermal spring, or geothermal spring is a spring produced by the emergence of geothermally heated groundwater onto the surface of the Earth. The groundwater is heated either by shallow bodies of magma (molten rock) or by circ ...

s. The pigment was originally discovered in 1849 by Swiss botanist Carl Nägeli, although the structure remained unsolved until 1993. It is an

aromatic In chemistry, aromaticity is a chemical property of cyclic ( ring-shaped), ''typically'' planar (flat) molecular structures with pi bonds in resonance (those containing delocalized electrons) that gives increased stability compared to satur ...

indole alkaloid Indole alkaloids are a class of alkaloids containing a structural moiety of indole; many indole alkaloids also include isoprene groups and are thus called terpene indole or secologanin tryptamine alkaloids. Containing more than 4100 known differe ...

built from two identical condensation products of

tryptophan Tryptophan (symbol Trp or W) is an α-amino acid that is used in the biosynthesis of proteins. Tryptophan contains an α-amino group, an α- carboxylic acid group, and a side chain indole, making it a polar molecule with a non-polar aromatic ...

yl- and tyrosyl-derived subunits linked through a carbon-carbon bond. Depending on the

redox Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate (chemistry), substrate change. Oxidation is the loss of Electron, electrons or an increase in the oxidation state, while reduction ...

conditions it can exist in two inter-convertible forms: a more common

oxidized Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a d ...

yellow-brown form which is insoluble in water and only slightly soluble in organic solvents, such as

pyridine Pyridine is a basic heterocyclic organic compound with the chemical formula . It is structurally related to benzene, with one methine group replaced by a nitrogen atom. It is a highly flammable, weakly alkaline, water-miscible liquid with a d ...

, and a reduced form with bright red color that is more soluble in organic solvents. Scytonemin absorbs very strongly and very broadly across the

UV-C Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30 PHz) to 400 nm (750 THz), shorter than that of visible light, but longer than X-rays. UV radiation i ...

UV-B Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30 PHz) to 400 nm (750 THz), shorter than that of visible light, but longer than X-rays. UV radiation i ...

- UV-A-

violet Violet may refer to: Common meanings * Violet (color), a spectral color with wavelengths shorter than blue * One of a list of plants known as violet, particularly: ** ''Viola'' (plant), a genus of flowering plants Places United States * Viol ...

blue Blue is one of the three primary colours in the RYB colour model (traditional colour theory), as well as in the RGB (additive) colour model. It lies between violet and cyan on the spectrum of visible light. The eye perceives blue when obs ...

spectral ''Spectral'' is a 2016 3D military science fiction, supernatural horror fantasy and action-adventure thriller war film directed by Nic Mathieu. Written by himself, Ian Fried, and George Nolfi from a story by Fried and Mathieu. The film stars J ...

region, with an

in vivo Studies that are ''in vivo'' (Latin for "within the living"; often not italicized in English) are those in which the effects of various biological entities are tested on whole, living organisms or cells, usually animals, including humans, and ...

maximum

absorption Absorption may refer to: Chemistry and biology * Absorption (biology), digestion **Absorption (small intestine) *Absorption (chemistry), diffusion of particles of gas or liquid into liquid or solid materials *Absorption (skin), a route by which ...

at 370 nm and an

in vitro ''In vitro'' (meaning in glass, or ''in the glass'') studies are performed with microorganisms, cells, or biological molecules outside their normal biological context. Colloquially called "test-tube experiments", these studies in biology an ...

maximum absorption at 386 and 252 nm, and with smaller peaks at 212, 278 and 300 nm. It is believed that scytonemin acts as a highly efficient protective biomolecule (

sunscreen Sunscreen, also known as sunblock or sun cream, is a photoprotective topical product for the skin that mainly absorbs, or to a much lesser extent reflects, some of the sun's ultraviolet (UV) radiation and thus helps protect against sunburn and ...

) that filters out damaging high frequency UV rays while at the same time allowing the transmittance of wavelengths necessary for

photosynthesis Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored i ...

. Its

biosynthesis Biosynthesis is a multi-step, enzyme-catalyzed process where substrates are converted into more complex products in living organisms. In biosynthesis, simple compounds are modified, converted into other compounds, or joined to form macromolecules. ...

in cyanobacteria is mostly triggered by exposure to UV-A and UV-B wavelengths. Recently, Couradeau and coworkers found that cyanobacterial soil crusts warm the soil surface by as much as 10 °C through the production and accumulation of scytonemin pigments. This effect is due to the dissipation of the absorbed

photon A photon () is an elementary particle that is a quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons are massless, so they always ...

s by the scytonemin molecules into

heat In thermodynamics, heat is defined as the form of energy crossing the boundary of a thermodynamic system by virtue of a temperature difference across the boundary. A thermodynamic system does not ''contain'' heat. Nevertheless, the term is al ...

Biosynthesis

The biosynthesis in ''Lyngbya aestuarii'' was recently explored by Balskus, Case, and Walsh. It proceeds by the conversion of

L-tryptophan Tryptophan (symbol Trp or W) is an α-amino acid that is used in the biosynthesis of proteins. Tryptophan contains an Alpha_and_beta_carbon , α-amino group, an α-carboxylic acid group, and a side chain indole, making it a polar molecule with ...

to 3-indole pyruvic acid, followed by coupling to ''p''-hydroxyphenylpyruvic acid. Cyclization of the resultant β-ketoacid yields a tricyclic ketone. Oxidation and dimerization yields the completed natural product. Three scytonemin biosynthetic enzymes are necessary, denoted as ScyA-C.{{cite journal, last1=Balskus, first1=Emily P., last2=Case, first2=Rebecca J., last3=Walsh, first3=Christopher T., year=2011, title=The biosynthesis of cyanobacterial sunscreen scytonemin in intertidal microbial mat communities, journal=FEMS Microbiology Ecology, volume=77, issue=2, pages=1–11, doi=10.1111/j.1574-6941.2011.01113.x, pmid=21501195, url=https://dash.harvard.edu/bitstream/handle/1/12169551/nihms292647.pdf?sequence=1, pmc=3134115

References

Biological pigments Secondary metabolites Cyanobacteria