Raman spectroscopic search for scytonemin and gloeocapsin in endolithic colonizations in large gypsum crystals

Rock-dwelling microorganisms are frequently exposed to intense UV-radiation, and thus, they synthesize specialized UV-protective pigments. In this study, Raman microspectrometry was used for analysis of noncarotenoid UV-protective pigments of dark-pigmented endolithic colonization found in gypsum outcrops from three areas (Sicily, Poland and Israel). Samples were investigated using 445-, 532- and 780-nm excitation lasers. Two noncarotenoid UV-protective pigments scytonemin and gloeocapsin were detected in all studied sites. Major Raman bands of scytonemin were found at around 1593, 1552, 1438 and 1173 cm(-1). Gloeocapsin shows characteristic Raman bands similar to anthraquinone-based parietin of lichens: at 1665, 1575, 1378, 1310 and 465 cm(-1). Scytonemin and gloeocapsin are highly specific for cyanobacteria and therefore can be used as biomarkers of certain taxa of cyanobacteria. Detection of such pigments by Raman spectroscopy using three excitation wavelengths allows to gather more information about the composition of endolithic consortia using relatively fast and noninvasive methods and in their natural habitats.

Automated summary

Rock-dwelling microorganisms synthesize specialized UV-protective pigments to cope with intense UV-radiation. Raman microspectrometry was used to analyze noncarotenoid UV-protective pigments in dark-pigmented endolithic colonization from gypsum outcrops in Sicily, Poland, and Israel. Two specific pigments, scytonemin and gloeocapsin, were identified as biomarkers for certain taxa of cyanobacteria. The study demonstrates the potential of Raman spectroscopy in providing fast and noninvasive methods for characterizing endolithic consortia in their natural habitats.