Compatible Solutes and Extremolytes
Compatible solutes are ubiquitous and are found in all three domains of life. They accumulate to high concentrations in cells in response to diverse environmental stresses (e.g.heat, cold, osmotic stress, and desiccation) without interfering with cellular metabolism and allow their hosts to survive harsh environmental conditions by stabilizing and protecting biomolecular structures and the cellular conformation. Compatible solutes can be either taken up from the environment by the cell or are formed via de-novo synthesis. Many different compatible solutes are known that can be subdivided into different chemical categories such as (i) amino acids (e.g. α-glutamate, β-glutamate) and amino acid derivatives (e.g. glycine-betaine, ectoine, hydroxyectoine) as well as (ii) sugars (e.g. trehalose, MG), polyols (e.g. glycerol) and derivatives (51). Because of their protective effect on biological structures such as enzymes, DNA, membranes and whole cells, the compatible solutes have found commercial applications in different industrial fields such as food, health and consumer care and cosmetics.
Extremolytes are compatible solutes that are exclusively found in extremophiles and especially (hyper)thermophiles but not in mesophilic organisms. Such extremolytes include cyclic 2,3-di-phosphoglycerate (cDPG), di-myo-1,1’-inositol-phosphate (DIP) and mannosylglycerate (MG). However, their potential for industrial/biotechnological applications remains largely unexploited, mainly because efficient synthesis pathways to make their production economically viable are missing.