Analysis of brown, violet and blue pigments of microorganisms by Raman spectroscopy

Raman spectroscopy allows the detection and discrimination between microbial pigments of different origins, including carotenoids, chlorophylls and less commonly found violet and brown non-photosynthetic pigments. This review reports examples of Raman spectroscopic studies on violet and brown pigments produced by microorganisms. Examples of investigations on the biological pigments scytonemin, gloeocapsin, violacein, phycocyanin, and prodigiosin are reviewed. Raman spectroscopy is a fast, simple and direct analytical tool which has been appreciated by microbiologists and chemists but more recently also by those who study natural geobiological processes in real-world systems. Different Raman spectroscopic approaches including confocal Raman spectrometry, FT-Raman spectroscopic possibilities, and SERS modes are reviewed for possibilities of following distribution of pigments at the cellular level in microbial cultures or in native endoliths, including confocal Raman spectrometry, FT-Raman spectroscopic possibilities, and SERS modes. New fast Raman mapping techniques are increasingly used, as well as portable systems. Special possibilities of high relevance for geoscience, geobiology or applied microbiology are opened up by the recent revolutionary technical developments, including the availability of portable and handheld tools that can be used directly on rocky outcrops to study native microbial colonization in situ.