Biological sources, metabolism, and production of glucosylglycerols, a group of natural glucosides of biotechnological interest

Glucosylglycerols (GGs) are a group of functional heterosides comprising glycerol and glucose. In nature, they are mainly produced by many moderately salt-tolerant cyanobacteria as compatible solutes in a salt-dependent manner and synthesized in a few higher plants and fermentation processes. Because of their many interesting physicochemical properties and biological activities, such as low sweetness, low hygroscopicity, high water-holding capacity, excellent biocompatibility, favorable performance in protecting macromolecules, and antitumor activity, GGs exhibit large application potential in the fields of cosmetics, health care, food service, enzyme production, and pharmaceuticals. Many in vitro systems using different members of the GH (glycoside hydrolase) family have been established for the enzymatic synthesis of GGs, and a few of them are in use for commercial production. Based on a good understanding of the genetic bases, biochemical processes, and regulatory mechanisms of GG metabolism in microorganisms (mainly cyanobacteria), in recent years GG production technologies with in vivo systems have also been developed by applying metabolic and bioprocess engineering to a few native or heterologous microbial cell factories. This successfully provides the market GG products with an alternative source. With the further elucidation of details about the biological functions of GGs and related mechanisms, the application scope of GGs will be greatly expanded. In the present review, the biological sources and physiological roles of GGs, the molecular bases and regulation of GG metabolism, and the recent progress in GG production and application are systematically summarized. A few new questions that have arisen in the basic research of GGs and perspectives on GG application are also discussed.