Susana E. Jorge-Villar

Raman and SEM analysis of a biocolonised hot spring travertine terrace in Svalbard, Norway

BackgroundA profile across 8 layers from a fossil travertine terrace from a low temperature geothermal spring located in Svalbard, Norway has been studied using both Raman spectroscopy and SEM (Scanning Electron Microscopy) techniques to identify minerals and organic life signals.ResultsCalcite, anatase, quartz, haematite, magnetite and graphite as well as scytonemin, three different carotenoids, chlorophyll and a chlorophyll-like compound were identified as geo- and biosignatures respectively, using 785 and/or 514 nm Raman laser excitation wavelengths. No morphological biosignatures representing remnant microbial signals were detected by high-resolution imaging, although spectral analyses indicated the presence of organics. In contrast, in all layers, Raman spectra identified a series of different organic pigments indicating little to no degradation or change of the organic signatures and thus indicating the preservation of fossil biomarker compounds throughout the life time of the springs despite the lack of remnant morphological indicators.ConclusionWith a view towards planetary exploration we discuss the implications of the differences in Raman band intensities observed when spectra were collected with the different laser excitations. We show that these differences, as well as the different detection capability of the 785 and 514 nm laser, could lead to ambiguous compound identification. We show that the identification of bio and geosignatures, as well as fossil organic pigments, using Raman spectroscopy is possible. These results are relevant since both lasers have been considered for miniaturized Raman spectrometers for planetary exploration.

Microorganism Response to Stressed Terrestrial Environments: A Raman Spectroscopic Perspective of Extremophilic Life Strategies

Raman spectroscopy is a valuable analytical technique for the identification of biomolecules and minerals in natural samples, which involves little or minimal sample manipulation. In this paper, we evaluate the advantages and disadvantages of this technique applied to the study of extremophiles. Furthermore, we provide a review of the results published, up to the present point in time, of the bio- and geo-strategies adopted by different types of extremophile colonies of microorganisms. We also show the characteristic Raman signatures for the identification of pigments and minerals, which appear in those complex samples.

Raman spectroscopy of volcanic lavas and inclusions of relevance to astrobiological exploration

Volcanic eruptions and lava flows comprise one of the most highly stressed terrestrial environments for the survival of biological organisms; the destruction of botanical and biological colonies by molten lava, pyroclastic flows, lahars, poisonous gas emissions and the deposition of highly toxic materials from fumaroles is the normal expectation from such events. However, the role of lichens and cyanobacteria in the earlier colonization of volcanic lava outcrops has now been recognized. In this paper, we build upon earlier Raman spectroscopic studies on extremophilic colonies in old lava flows to assess the potential of finding evidence of biological colonization in more recent lava deposits that would inform, first, the new colonization of these rocks and also provide evidence for the relict presence of biological colonies that existed before the volcanism occurred and were engulfed by the lava. In this research, samples were collected from a recent expedition to the active volcano at Kilauea, Hawaii, which comprises very recent lava flows, active fumaroles and volcanic rocks that had broken through to the ocean and had engulfed a coral reef. The Raman spectra indicated that biological and geobiological signatures could be identified in the presence of geological matrices, which is encouraging for the planned exploration of Mars, where it is believed that there is evidence of an active volcanism that perhaps could have preserved traces of biological activity that once existed on the planet’s surface, especially in sites near the old Martian oceans.

Raman spectroscopic analysis of arctic nodules: relevance to the astrobiological exploration of Mars

AbstractThe discovery of small, spherical nodules termed ‘blueberries’ in Gusev Crater on Mars, by the NASA rover Opportunity has given rise to much debate on account of their interesting and novel morphology. A terrestrial analogue in the form of spherical nodules of similar size and morphology has been analysed using Raman spectroscopy; the mineralogical composition has been determined and evidence found for the biological colonisation of these nodules from the spectral signatures of cyanobacterial protective biochemical residues such as scytonemin, carotenoids, phycocyanins and xanthophylls. This is an important result for the recognition of future sites for the planned astrobiological exploration of planetary surfaces using remote robotic instrumentation in the search for extinct and extant life biosignatures and for the expansion of putative terrestrial Mars analogue geological niches and morphologies. FigureRed and yellowish-green chasmoliths and the green endolithic community on the third rock sample analysed (©Storvik/AMASE)

Raman spectroscopy study of lichens using three spectrometers under different experimental conditions: analyses of the results with relevance for extraplanetary exploration

We have carried out analyses on three extremophile lichens from the Tabernas Desert (Spain) under different experimental conditions: dry and wet samples in the laboratory and wet specimens in the field, using three spectrometers: one portable, one FT-Raman and one dispersive micro-Raman instruments. Apart from pigment characterization, the information obtained from the spectra is compared and the differences analysed. The fact that no results were achieved on dry lichens using the handheld spectrometer is of special relevance for those looking for life in hazardous environments. Since in some extreme habitats, life could be “dormant” and only activates under appropriate conditions, miniaturized instruments (such as those included for extraplanetary exploration missions) could not detect bio-markers and, then, life signals will not be noticed when, actually, life is there. Furthermore, we show in this work, using the miniaturized Raman spectrometer, that not only laser wavelength, spectral resolution and wavenumber region of the spectrum are important for the bio- or geo-marker recognition but also spot-size is of vital relevance for the unambiguous biomolecular characterization. In our opinion, mini-Raman instruments are useful for assessing in situ the eventual presence of bio-markers in complex natural samples, such as organisms, but are not accurate enough for precise molecular identification.

Lichens around the world: a comprehensive study of lichen survival biostrategies detected by Raman spectroscopy

A list of lichen biomolecules detected by Raman spectroscopy has been compiled and their appearance has been correlated with the environmental conditions operating in lichen habitats around the world. The adaptative climatic strategies of lichens have been analysed as a whole and some interesting and contradictory conclusions arise with regard to other research conclusions reported in the literature, such as the presence of hydrated calcium oxalates and their relationship with desiccated environments or the correlation between climatic conditions and protective pigments or pigment mixtures. The results of this exercise will be useful for our understanding of the biochemical synthetic strategies being employed for the survival of the lichen colonies in hostile terrestrial environments and the prediction of Raman spectral data for extremophiles in a range of novel hot and cold desert conditions. Additionally, a database of all key lichen biomolecules identified by Raman spectroscopy and their characteristic Raman wavenumbers are given for further unambiguous identification.

Raman spectroscopic analysis of the effect of the lichenicolous fungus Xanthoriicola physciae on its lichen host.

Lichenicolous (lichen-dwelling) fungi have been extensively researched taxonomically over many years, and phylogenetically in recent years, but the biology of the relationship between the invading fungus and the lichen host has received limited attention, as has the effects on the chemistry of the host, being difficult to examine in situ. Raman spectroscopy is an established method for the characterization of chemicals in situ, and this technique is applied to a lichenicolous fungus here for the first time. Xanthoriicola physciae occurs in the apothecia of Xanthoria parietina, producing conidia at the hymenium surface. Raman spectroscopy of apothecial sections revealed that parietin and carotenoids were destroyed in infected apothecia. Those compounds protect healthy tissues of the lichen from extreme insolation and their removal may contribute to the deterioration of the apothecia. Scytonemin was also detected, but was most probably derived from associated cyanobacteria. This work shows that Raman spectroscopy has potential for investigating changes in the chemistry of a lichen by an invading lichenicolous fungus.

Lichen biomarkers upon heating: a Raman spectroscopic study with implications for extra-terrestrial exploration

Lithopanspermia Theory has suggested that life was transferred among planets by meteorites and other rocky bodies. If the planet had an atmosphere, this transfer of life had to survive drastic temperature changes in a very short time in its entry or exit. Only organisms able to endure such a temperature range could colonize a planet from outer space. Many experiments are being carried out by NASA and European Space Agency to understand which organisms were able to survive and how. Among the suite of instruments designed for extraplanetary exploration, particularly for Mars surface exploration, a Raman spectrometer was selected with the main objective of looking for life signals. Among all attributes, Raman spectroscopy is able to identify organic and inorganic compounds, either pure or in admixture, without requiring sample manipulation. In this study, we used Raman spectroscopy to examine the lichen Squamarina lentigera biomarkers. We analyse spectral signature changes after sample heating under different experimental situations, such as (a) laser, (b) analysis accumulations over the same spot and (c) environmental temperature increase. Our goal is to evaluate the capability of Raman spectroscopy to identify unambiguously life markers even if heating has induced spectral changes, reflecting biomolecular transformations. Usnic acid, chlorophyll, carotene and calcium oxalates were identified by the Raman spectra. From our experiments, we have seen that usnic acid, carotene and calcium oxalates (the last two have been suggested to be good biomarkers) respond in a different way to environmental heating. Our main conclusion is that despite their abundance in nature or their inorganic composition the resistance to heat makes some molecules more suitable than others as biomarkers.

The Servilia tomb: an architecturally and pictorially important Roman building

One hundred and eleven samples from the important Servilia Roman tomb have been analysed for the first time by Raman spectroscopy, resulting in a complete characterisation of the pigment palette used for its remarkable wall paintings: 73 different pigment mixtures have been identified for the composition of its 11 colours and their tonalities. Dyer’s weld, an ancient organic yellow pigment, which was described by Vitruvius, has been identified and characterised for the first time in Roman wall paintings. Distinctive Raman spectroscopic signals which differentiate between haematite and caput mortuum (a violet colour from haematite which has been subjected to thermal treatment) are also reported. The use of the very expensive lazurite for a balance relates the importance of this otherwise ordinary instrument with psychostasia (the human soul weighing process) and is not found elsewhere in the tomb. The distribution of white minerals alone or in admixture is not related to any particular colouring pigment or figure; this possibly indicates that there was no specific use for each white mineral and that several craftsmen worked on the paintings, perhaps in different periods, or that the frescoes have been subjected to unrecorded restoration. We conclude that Raman spectroscopy is a valuable analytical technique for the unambiguous identification of mixtures of both organic and inorganic compounds, to study the degree of mineral crystallinity and for identifying treatment. These data are relevant for the holistic interpretation of the artwork in its historical, economical and social context.