osmolyte

Osmolytes are small organic molecules that organisms accumulate or synthesize to regulate cellular osmotic balance. They are often described as compatible solutes because they can be present at high intracellular concentrations without disrupting normal metabolism. Osmolytes help cells maintain turgor and volume when external solute levels are high, water is scarce, or temperatures change.

Common osmolytes include amino acids and derivatives such as proline and glycine betaine; sugars and polyols such as trehalose, glycerol, and sorbitol; and other compatible compounds such as taurine and trimethylamine N-oxide (TMAO). Some microorganisms produce unique osmolytes like ectoine; plants commonly accumulate proline and glycine betaine, while yeasts often use glycerol.

They act by adjusting intracellular osmolarity to reduce water efflux, and by stabilizing proteins and membranes through hydration shell effects and preferential exclusion from protein surfaces, helping to preserve structure and function under stress. They may also protect enzymes during dehydration and temperature extremes and, in some systems, participate in reactive oxygen species defense.

Osmolytes are found in bacteria, archaea, fungi, plants, algae, and some animals. They can be synthesized de novo via distinct biosynthetic pathways or transported into the cell by dedicated uptake systems, enabling rapid responses to environmental changes.

Understanding osmolyte accumulation informs approaches to improve crop tolerance to drought and salinity, stabilize industrial enzymes and bioprocesses, and preserve biological samples.