Microorganisms inhabiting gypsum have been observed in environments that differ greatly in water availability. Gypsum colonized by microorganisms, including cyanobacteria, eukaryotic algae, and diverse heterotrophic communities, occurs in hot, arid or even hyperarid environments, in cold environments of the Antarctic and Arctic zones, and in saline and hypersaline lakes and ponds where gypsum precipitates. Fossilized microbial remnants preserved in gypsum were also reported. Gypsum protects the endolithic microbial communities against excessive insolation and ultraviolet radiation, while allowing photosynthetically active radiation to penetrate through the mineral substrate. We here review the worldwide occurrences of microbially colonized gypsum and the specific properties of gypsum related to its function as a substrate and habitat for microbial life on Earth and possibly beyond. Methods for detecting and characterizing endolithic communities and their biomarkers in gypsum are discussed, including microscopic, spectroscopic, chemical, and molecular biological techniques. The modes of adaptation of different microorganisms to life within gypsum crystals under different environmental conditions are described. Finally, we discuss gypsum deposits as possible targets for the search for microbial life or its remnants beyond Earth, especially on Mars, where sulfate-rich deposits occur, and propose strategies to detect them during space exploration missions.

• Keywords
• astrobiology, biomarkers, cyanobacteria, endolithic communities, gypsum,
• Publication type
• Journal Article MeSH
• Review MeSH

A prototype instrument, under development at the University of Leicester, for the future European Space Agency (ESA) ExoMars mission, was used for the analysis of microbial pigments within a stratified gypsum crust from a hypersaline saltern evaporation pond at Eilat (Israel). Additionally, the same samples were analysed using a miniaturized Raman spectrometer, featuring the same 532 nm excitation. The differences in the position of the specific bands, attributed to carotenoid pigments from different coloured layers, were minor when analysed by the ESA prototype instrument; therefore, making it difficult to distinguish among the different pigments. The portable Delta Nu Advantage instrument allowed for the discrimination of microbial carotenoids from the orange/green and purple layers. The purpose of this study was to complement previous laboratory results with new data and experience with portable or handheld Raman systems, even with a dedicated prototype Raman system for the exploration of Mars. The latter is equipped with an excitation wavelength falling within the carotenoid polyene resonance region. The ESA prototype Raman instrument detected the carotenoid pigments (biomarkers) with ease, although further detailed distinctions among them were not achieved.

• Keywords
• Mars, Raman, gypsum, halophiles, pigments, prototype,
• Publication type
• Journal Article MeSH

Raman spectroscopy is a rapid nondestructive technique providing spectroscopic and structural information on both organic and inorganic molecular compounds. Extensive applications for the method in the characterization of pigments have been found. Due to the high sensitivity of Raman spectroscopy for the detection of chlorophylls, carotenoids, scytonemin, and a range of other pigments found in the microbial world, it is an excellent technique to monitor the presence of such pigments, both in pure cultures and in environmental samples. Miniaturized portable handheld instruments are available; these instruments can be used to detect pigments in microbiological samples of different types and origins under field conditions.

• MeSH
• Archaea chemistry   MeSH
• Bacteria chemistry   MeSH
• Pigments, Biological analysis   MeSH
• Fungi chemistry   MeSH
• Spectrum Analysis, Raman methods   MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Review MeSH
• Names of Substances
• Pigments, Biological MeSH

Raman spectroscopy plays a major role in robust detection of biomolecules and mineral signatures in halophile research. An overview of Raman spectroscopic investigations in halophile research of the last decade is given here to show advantages of the approach, progress made as well as limits of the technique. Raman spectroscopy is an excellent tool to monitor and identify microbial pigments and other biomolecules in extant and extinct halophile biomass. Studies of bottom gypsum crusts from salterns, native evaporitic sediments, halite inclusions, and endoliths as well as cultures of halophilic microorganisms permitted to understand the content, distribution, and behavior of important molecular species. The first papers describing Raman spectroscopic detection of microbiological and geochemical key markers using portable instruments are highlighted as well.

• Keywords
• Raman spectroscopy, carotenoids, compatible solutes, gypsum crusts, halophilic, salterns,
• Publication type
• Journal Article MeSH
• Review MeSH

Raman spectroscopy is being adopted as a nondestructive instrumentation for the robotic exploration of Mars to search for traces of life in the geological record. Here, miniaturized Raman spectrometers of two different types equipped with 532 and 785 nm lasers for excitation, respectively, were compared for the detection of microbial biomarkers in natural halite from the hyperarid region of the Atacama Desert. Measurements were performed directly on the rock as well as on the homogenized, powdered samples prepared from this material-the effects of this sample preparation and the excitation wavelength employed in the analysis are compared and discussed. From these results, 532 nm excitation was found to be superior for the analysis of powdered specimens due to its high sensitivity toward carotenoids and hence a higher capability for their detection at relatively low concentration in bulk powdered specimens. For the same reason, this wavelength was a better choice for the detection of carotenoids in direct measurements made on the rock samples. The 785 nm excitation wavelength, in contrast, proved to be more sensitive toward the detection of scytonemin.

• MeSH
• Biomarkers analysis   MeSH
• Phenols analysis   MeSH
• Indoles analysis   MeSH
• Carotenoids analysis   MeSH
• Mars * MeSH
• Extraterrestrial Environment chemistry   MeSH
• Minerals chemistry   MeSH
• Spectrum Analysis, Raman * MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Biomarkers MeSH
• Phenols MeSH
• Indoles MeSH
• Carotenoids MeSH
• Minerals MeSH
• scytonemin MeSH Browser

We explored the use of Raman spectroscopy to detect organic osmotic solutes as biomarkers in the moderately halophilic heterotrophic bacterium Halomonas elongata grown in complex medium (accumulation of glycine betaine) and in defined medium with glucose as carbon source (biosynthesis of ectoine), and in the anoxygenic phototrophic Ectothiorhodospira marismortui known to synthesize glycine betaine in combination with minor amounts of trehalose and N-α-carbamoyl glutamineamide. We tested different methods of preparation of the material: lyophilization, two-phase extraction of water-soluble molecules, and perchlorate extraction. Raman signals of glycine betaine and ectoine were detected; perchlorate extraction followed by desalting the extract on an ion retardation column gave the best results. Lyophilized cells of E. marismortui showed strong signals of carotenoid pigments, and glycine betaine could be detected only after perchlorate extraction and desalting. The data presented show that Raman spectroscopy is a suitable tool to assess the mode of osmotic adaptation used by halophilic microorganisms.

• MeSH
• Betaine chemistry   metabolism   MeSH
• Ectothiorhodospira chemistry   metabolism   MeSH
• Halomonas chemistry   metabolism   MeSH
• Spectrum Analysis, Raman methods   MeSH
• Trehalose chemistry   metabolism   MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Betaine MeSH
• Trehalose MeSH