Raman spectroscopic screening of cyanobacterial chasmoliths from crystalline gypsum—The Messinian crisis sediments from Southern Sicily

Abstract

This study shows the first results on Raman spectroscopic investigations of pigments from cyanobacterial endolithic colonisations in gypsum of Messinian age (Miocene). Gypsum from outcrops of sedimentary series close to Eraclea Minoa (Sothern Sicily) is sometimes inhabited by endoliths. Raman spectroscopic investigations allow to specify type of colonisation through identification of their pigments. Coccoid cyanobacteria (Chroococcidiopsis sp., Gloeocapsopsis pleurocapsoides, Gloeocapsa compacta, and Synechococcus sciophilus), filamentous heterocytous Nostoc sp., and filamentous bundle‐forming Symplocastrum cf. aurantiacum and Microcoleus sp. were found to inhabit different parts of the gypsum samples. Carotenoids (as assumed frequently β‐carotene) are produced in all the samples studied (optimised detection using 514‐nm excitation), scytonemin in the samples colonised by G. pleurocapsoides (G1, G2, and G6), and phycobiliproteins in the sample G3 (those detected using 785‐nm excitation). This study is the first initiative to collect better knowledge on detecting biomarker traces in the frame of Messinian‐age gypsum sequence of relevance for old Martian environments.

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

“…As already mentioned, in our previous study, several chips of colonised gypsum from the site west from Scala dei Turchi (close to Torre Salsa) were investigated by Raman microspectrometry 49 . The ν 1 bands of carotenoids were observed in the interval of 1,509–1,519 cm −1 .…”

“…Carotenoids were the predominant pigments detected. However, Raman spectra of other pigments (e.g., scytonemin and phycobiliproteins) were recorded using near infrared excitation (785 nm) as well 49 . This wavelength also allowed detection of scytonemin in halite using a portable Raman spectrometer 68 .…”

“…Our previous study reported the first description of gypsum endolithic colonisations in the seaside site Torre Salsa (Southern Sicily, ~33 km west of Agrigento) 49 . Few chips of gypsum and selenitic aggregates were screened for the presence of cyanobacteria.…”

“…Besides that, scytonemin (1,605, 1,592 and 1,172 cm −1 ) was also detected using a 514.5‐nm laser. Carotenoids and scytonemin were also discriminated by the laboratory instrument using a 785‐nm laser, which also allowed detection of other pigments—chlorophyll (1,327, 1,185, 987, 948 and 746 cm −1 ) and phycobiliproteins (1,633, 1,584, 1,371, 1,236, 813 and 667 cm −1 ) 49 …”

GeoRaman

“…Astrobiology studies sometimes are based on the investigation of life in Earth environments similar to those expected on extraterrestrial bodies. Jehlička et al [32] use the Raman signature of pigments produced by cyanobacteria to study the endolithic bio-colonization in Messinian crisis sediments from Southern Sicily, similar to Martian environment.…”