In this paper, it is demonstrated how Raman spectroscopy can be used to detect different carotenoids as possible biomarkers in various groups of microorganisms. The question which arose from previous studies concerns the level of unambiguity of discriminating carotenoids using common Raman microspectrometers. A series of laboratory-grown microorganisms of different taxonomic affiliation was investigated, such as halophilic heterotrophic bacteria, cyanobacteria, the anoxygenic phototrophs, the non-halophilic heterotrophs as well as eukaryotes (Ochrophyta, Rhodophyta and Chlorophyta). The data presented show that Raman spectroscopy is a suitable tool to assess the presence of carotenoids of these organisms in cultures. Comparison is made with the high-performance liquid chromatography approach of analysing pigments in extracts. Direct measurements on cultures provide fast and reliable identification of the pigments. Some of the carotenoids studied are proposed as tracers for halophiles, in contrast with others which can be considered as biomarkers of other genera. The limits of application of Raman spectroscopy are discussed for a few cases where the current Raman spectroscopic approach does not allow discriminating structurally very similar carotenoids. The database reported can be used for applications in geobiology and exobiology for the detection of pigment signals in natural settings.
Since evaporitic rocks on the Martian surface could (or still can) serve as potential habitats for microbial life on Mars, there is a reasonable possibility that these rocks may sustain molecular remnants as evidence for the presence of extinct or extant living organisms on Mars and that beta-carotene could be a suitable biomarker. In this paper, Raman microspectrometry was tested as a nondestructive method of determining the lowest detectable beta-carotene content in experimentally prepared evaporitic matrices--namely, gypsum, halite and epsomite. Two excitation wavelengths were compared--514.5 nm, because of the resonance Raman enhancement in the carotenoid analysis, and 785 nm, as a more universal wavelength now much used in the detection of biomolecules terrestrially. Mixtures were measured directly as well as with a laser beam penetrating the crystals of gypsum and epsomite. We have obtained beta-carotene signals at the 0.1 to 10 mg kg(-1) level--the number of registered beta-carotene Raman bands differed depending on the particular mineral matrix and the excitation wavelength. Concentrations of beta-carotene of about one order of magnitude higher were identified when analysed through single crystals of gypsum and epsomite, respectively.
Flexirubins are specific polyene pigments produced by several genera of Bacteroidetes. Colonies and cell extracts of Flavobacterium johnsoniae and Flexibacter elegans have been investigated by Raman spectroscopy to show that this fast and non-destructive technique can be used to differentiate these pigments from carotenoids and to compare the flexirubin content of the two microorganisms. The presence or absence of certain distinguishing features in the CH combination band region at 2500-2750 cm(-1) can assist in the discrimination between the two flexirubins investigated. Raman spectroscopy is thus a suitable tool not only to detect flexirubin pigments in bacterial cells, but also to further characterize the pigments present in members of the Bacteroidetes genera that are rich in flexirubins.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.