Detecting microbial pigments from gypsum using Raman spectroscopy: from field prospection to laboratory studies

<p>Terrestrial detection of biomarkers in various mineral matrices using Raman spectrometers including field deploying of miniature instrumentation in Mars-analogue sites can be seen as a training for next Martian missions. In fact, both the European Space Agency (Exomars) and North American Space Agency (Mars 2020) robotic rovers will include Raman spectrometers. Feasibility of detecting biomarkers of extremophilic cyanobacteria and algae (pigments, osmotic solutes and lipids) using Raman microspectrometry was reviewed previously. Here the idea is to show - firstly how portable Raman instrumentation permits to detect carotenoids fast and onsite under field conditions. Secondly, laboratory microspectrometric investigations allow to obtain more detailed information about spatial distribution of pigments originating from microorganisms.</p><p>Macrocrystalline gypsum layers and aggregates are well-known from Tertiary series in Sicily and Eastern Poland. In Southern Sicily gypsum sediments accumulated during Messinian crisis (Late Miocene) are outcroping and were investigated near Scala dei Turchi, Torre Salsa and Siculiana Marina. Polish Tertiary (Badenian, Middle Miocene) examples of gypsum colonisations of decimetre long outcropping crystals were studied near Chotel Czerwony, Skorocice and Chwalowice. Miniature portable Raman spectrometers equipped with green lasers allowing recording of resonance Raman signals of carotenoids are evaluated here. Possibilities of collecting spectra of carotenoids under non-resonant conditions using a portable sequentially shifted Raman spectrometer (785 and 853nm lasers) are shown as well. Observed shifts of positions of Raman features of carotenoids between gypsum samples (and sites) are discussed and critically evaluated. In addition, acquired data are compared to data obtained through laboratory Raman microspectrometric investigations. Selected zones of microbial colonisations of few types of gypsum are described from the point of view of the presence of algae and cyanobacteria. Pigments are detected through conventional Raman microspectrometric measurements. Carotenoids were documented in major part of samples (common Raman bands at around 1525, 1157, and 1004 cm<sup>−1</sup>). Additionally, Raman spectra of other pigments were recorded in several zones using near infrared excitation (785 nm): chlorophyll (1151, 1327, 1287, 1184, 917, and 745 cm<sup>−1</sup>), scytonemin (1593, 1152, 1438, and 1173 cm<sup>−1</sup>) and phycobiliproteins (1633, 1584, 1371, 1236, 813, and 667 cm<sup>−1</sup>).</p><p>Portable instrumentation permits detection of carotenoids in gypsum fast and onsite under field conditions. Raman microspectrometric investigations of colonisations allow to gather detailed information about pigment distribution in micrometric zones of gypsum samples.</p>

Thoughts on the “missing link” between saltworks biology and solat salt quality

Although solar salterns worldwide use seawater of identical chemical composition as the raw material for salt production, the size and quality of the halite crystals that precipitate in the crystallizer ponds is highly variable. Biological processes have been implicated to be responsible for the differences observed, but the “missing link” between saltworks biology and solar salt quality has never unequivocally been identified. This paper presents an overview of the different organic chemicals that are formed by the members of the microbial communities in saltern evaporation and crystallizer ponds as osmotic stabilizers as well as different compounds formed during further microbial metabolism of those osmotic solutes. Examination of the in situ concentrations and the possible role of glycerol, glycine betaine, ectoine, dihydroxyacetone, acetate, lactate, and other organic compounds failed to identify one or more compounds that may accumulate at concentrations high enough to significantly modify the formation of sodium chloride crystals in the salterns and to negatively influence the quality of the salt produced.