Fast screening of carotenoids of gypsum endoliths using portable Raman spectrometer (Messinian gypsum, Sicily)

Abstract

We tested the potential of a portable Raman spectrometer—RaPort (G) by EnSpectr with a 532‐nm laser for use in field detection of biomarkers of endolithic colonization in gypsum. This study extends our previous research on gypsum endolithic colonies using laboratory Raman microspectrometer (514.5‐ and 785‐nm lasers). In the current study, variously coloured layers were found and screened separately on the outcrop under natural conditions. In the recorded Raman spectra, stretching vibrations of carotenoids were observed—ν1 (C═C) around 1,513 cm−1, and ν2 (C—C) around 1,154 cm−1, as well as the feature at around 1,005 cm−1. The exact identification of different carotenoids by portable Raman spectrometer is limited. Nevertheless, the portable Raman spectrometer allowed fast and in situ detection of carotenoids of variously pigmented gypsum endolithic zones. Application of miniature Raman instruments is important in the context of forthcoming astrobiological missions to Mars (Exomars and Mars 2020).

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

“…This research develops the Raman spectral investigations on endolithic colonizations in gypsum as already introduced in a Raman spectroscopic study on gypsum cyanobacteria from southern Sicily. [ 9,35 ] There, gypsum crystalline layers are outcropping and are frequently inhabited by endoliths. In the first study, mostly green and brown areas of the layered systems were investigated and Raman features documented the presence of chlorophyll (especially common in green), carotenoids (found in all the coloured zones), scytonemin (encountered in the dark zones) and also phycobiliproteins.…”

“…In the first study, mostly green and brown areas of the layered systems were investigated and Raman features documented the presence of chlorophyll (especially common in green), carotenoids (found in all the coloured zones), scytonemin (encountered in the dark zones) and also phycobiliproteins. More detail on the distribution of carotenoids was recently collected [ 53 ] on endoliths from Southern Sicily, and three newly observed sites of cyanobacterial colonization in large gypsum crystals in Eastern Poland were included. Raman spectra document the presence of different carotenoids in the samples, with their highest amount being found in the brick‐coloured strata corresponding to β‐carotene exclusively, in the case of samples colonized by the filamentous green alga Trentepohlia at Chotel Czerwony.…”

“…Colonized gypsum from the Siculiana Marina site was collected from a western‐oriented steep gypsum outcrop close to the road to the Siculiana Marina in southern Sicily (GPS: 37.338870 N, 13.396700 E) and is further described in our previous publication. [ 35 ] Black endolithic colonization was located between cleavage spaces of flat gypsum crystals (~10–15 cm in length; ~5 cm in width), whitish in colour and about 0.5–1 cm in distance from the surface. The colonies formed irregular biofilms of various sizes in the cleavage spaces of the gypsum crystals.…”

“…The majority of the previous studies in which Raman spectroscopy was used to collect salient information on the distribution of pigments in cyanobacterial colonies were reported mainly from fine‐grained gypsum aggregates, crusts and gypcretes [ 31,33 ] and only a few studies concentrated on larger transparent/translucent tabular type crystals. [ 9,35,43 ] Second, all the three sites seem much less extreme from the point of view of general physical/environmental conditions—in fact, Eastern Poland, Southern Sicily and even Galilee are areas with annual rain total in the range of 400–600 mm far removed from the 15 mm of Atacama or Namib deserts. The Raman spectra of carotenoids and some other pigments and their distributions were described previously from Sicilian gypsum.…”

“…[ 30,33 ] Additional spectroscopic information on these pigments can also be obtained by carrying‐out field in situ measurements on rocky outcrops using miniaturized instrumentation. [ 34–36 ]…”