title: Raman imaging in geomicrobiology: endolithic phototrophic microorganisms in gypsum from the extreme sun irradiation area in the Atacama Desert.
abstract: The Raman imaging method was successfully applied for mapping the distribution of biomolecules (e.g., pigments) associated with cryptoendolithic and hypoendolithic microorganisms, as well as the inorganic host mineral matrix that forms the habitat for the biota. To the best of our knowledge, this is the first comprehensive study in the field of geomicrobiology based on this technique. The studied microbial ecosystem was located nearly 3000 m above sea level within the driest desert on Earth, the Atacama in Chile. Enhancement of carotenoid Raman signal intensity close to the surface was registered at different areas of endolithic colonization dominated by algae, with cyanobacteria present as well. This is interpreted as an adaptation mechanism to the excessive solar irradiation. On the other hand, cyanobacteria synthesize scytonemin as a passive UV-screening pigment (found at both the hypoendolithic and cryptoendolithic positions). The distribution of the scytonemin Raman signal was mapped simultaneously with the surrounding mineral matrix. Thus, mapping was done of the phototrophic microorganisms in their original microhabitat together with the host rock environment. Important information which was resolved from the Raman imaging dataset of the host rock is about the hydration state of Ca-sulfate, demonstrated on the presence of gypsum (CaSO4·2H2O) and the absence of both anhydrite (CaSO4) and bassanite (CaSO4·1/2H2O). Obtaining combined "in situ" simultaneous information from the geological matrix (inorganic) together with the microbial biomolecules (organic) is discussed and concluded as an important advantage of this technique. We discuss how selection of the laser wavelength (785 and 514.5-nm) influences the Raman imaging results.
authors.affiliation: Global Change Research Institute, v.v.i., The Czech Academy of Sciences, Bělidla 4a, 603 00, Brno, Czech Republic. vitek.p@czechglobe.cz.
authors.forename: Petr
authors.initials: P
authors.lastname: Vítek
authors.affiliation: Museo Nacional de Ciencias Naturales, CSIC, c/Serrano 115 dpdo., 28006, Madrid, Spain.
authors.forename: Carmen
authors.initials: C
authors.lastname: Ascaso
authors.affiliation: Departamento Biología Vegetal, Ecología y Ciencias de la Tierra, Universidad de Extremadura, 10600, Plasencia, Spain.
authors.forename: Octavio
authors.initials: O
authors.lastname: Artieda
authors.affiliation: Museo Nacional de Ciencias Naturales, CSIC, c/Serrano 115 dpdo., 28006, Madrid, Spain.
authors.forename: Jacek
authors.initials: J
authors.lastname: Wierzchos
mesh_terms: D001419:Bacteria / Q000737:chemistry / Q000302:isolation & purification* / Q000378:metabolism / Q000528:radiation effects; D002133:Calcium Sulfate; D002338:Carotenoids / Q000032:analysis / Q000378:metabolism; D003889:Desert Climate; D017753:Ecosystem; D019015:Geologic Sediments / Q000737:chemistry / Q000382:microbiology*; D008027:Light; D013059:Spectrum Analysis, Raman / Q000379:methods*
chemical_list: D002338:Carotenoids; D002133:Calcium Sulfate
keywords: Adaptation strategy; Astrobiology; Carotenoids; Hyperspectral imaging; Mars; Photosynthesis