Raman spectra of osmotic solutes of halophiles

Organic osmotic solutes (compatible solutes) are accumulated within the cytoplasm of many microorganisms living in hypersaline environments to provide osmotic balance and to protect the cells against extreme osmotic pressure. Some hyperthermophilic prokaryotes also contain high intracellular concentrations of such compounds. A great diversity of organic osmotic solutes, including small sugars, sugar alcohols, amino acids, and amino acid derivatives, is found in nature. Thanks to the high concentrations in which these compounds are often present, Raman spectroscopy may be a useful technique for rapid analysis of such solute(s) both in individual organisms and in natural microbial communities in high-salt environments, including the possible use of portable miniaturised Raman spectrometers outdoors. Here, we present a database of Raman spectra of some of the most commonly encountered compatible solutes, as well as some less common ones such as ectoine, hydroxyectoine, glycine betaine, glucosylglycerol, mannosylglycerate (potassium salt), and di-myo-inositol phosphate, complementing existing information on the Raman spectra of other such solutes such as glycerol, sucrose, and trehalose. Spectra were collected using excitation at 785 nm, and assignment of the major bands was proposed. The data presented complement our knowledge of the spectroscopic characteristics of biomolecules and enable the rapid assessment of the mode of osmotic adaptation used by halophilic microorganisms in culture; this information may be used to obtain information on the distribution of the different solutes in extreme environments on earth and has the added potential for astrobiological applications to estimate the presence of such solutes in stressed environments elsewhere in the universe.