Cell suspensions of the haloarchaea Halorubrum sodomense and Halobacterium salinarum and the extremely halophilic bacterium Salinibacter ruber (Bacteroidetes) in saturated solutions of chlorides and sulfates (NaCl, KCl, MgSO4·7H2O, K2SO4, and (NH4)Al(SO4)2·12H2O) were left to evaporate to produce micrometric inclusions in laboratory-grown crystals. Raman spectra of these pinkish inclusions were obtained using a handheld Raman spectrometer with green excitation (532 nm). This portable instrument does not include any microscopic tool. Acceptable Raman spectra of carotenoids were obtained in the range of 200-4000 cm-1. This detection achievement was related to the mode of illumination and collection of scattered light as well as due to resonance Raman enhancement of carotenoid signals under green excitation. The position of diagnostic Raman carotenoid bands corresponds well to those specific carotenoids produced by a given halophile. To our best knowledge, this is the first study of carotenoids included in the laboratory in crystalline chlorides and sulfates, using a miniature portable Raman spectrometer. Graphical abstract ᅟ.

• Keywords
• Carotenoids, Halophilic prokaryotes, Inclusions, Miniature Raman spectrometer, Salts,
• MeSH
• Bacteroidetes chemistry   MeSH
• Potassium Chloride chemistry   MeSH
• Sodium Chloride chemistry   MeSH
• Halobacterium salinarum chemistry   MeSH
• Halorubrum chemistry   MeSH
• Carotenoids analysis   MeSH
• Limit of Detection MeSH
• Spectrum Analysis, Raman instrumentation   MeSH
• Sulfates chemistry   MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Potassium Chloride MeSH
• Sodium Chloride MeSH
• Carotenoids MeSH
• Sulfates MeSH

Laboratory cultures of a number of red extremely halophilic Archaea (Halobacterium salinarum strains NRC-1 and R1, Halorubrum sodomense, Haloarcula valismortis) and of Salinibacter ruber, a red extremely halophilic member of the Bacteria, have been investigated by Raman spectroscopy using 514.5nm excitation to characterize their carotenoids. The 50-carbon carotenoid α-bacterioruberin was detected as the major carotenoid in all archaeal strains. Raman spectroscopy also detected bacterioruberin as the main pigment in a red pellet of cells collected from a saltern crystallizer pond. Salinibacter contains the C40-carotenoid acyl glycoside salinixanthin (all-E, 2'S)-2'-hydroxy-1'-[6-O-(methyltetradecanoyl)-β-d-glycopyranosyloxy]-3',4'-didehydro-1',2'-dihydro-β,ψ-carotene-4-one), for which the Raman bands assignments of are given here for the first time.

• MeSH
• Bacteroidetes chemistry   MeSH
• Glycosides chemistry   isolation & purification   MeSH
• Haloarcula chemistry   MeSH
• Halobacteriaceae chemistry   MeSH
• Halobacterium salinarum chemistry   MeSH
• Halorubrum chemistry   MeSH
• Carotenoids chemistry   isolation & purification   MeSH
• Spectrum Analysis, Raman MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• bacterioruberin MeSH Browser
• Glycosides MeSH
• Carotenoids MeSH
• salinixanthin MeSH Browser