Glycine betaine: biosynthesis and biological function in halophilic microorganisms

Abstract:

Glycine betaine (i.e. trimethylglycine, N,N,N-trimethylglycine) plays a crucial role in halophilic microorganisms subjected to the long-term salt-stress and short-term salt-exposure. Two separate biosynthetic pathways of glycine betaine: the oxidation of choline and the methylation from glycine were found. The former is choline dehydrogenase (BetA) and betaine aldehyde dehydrogenase (BetB) using choline as substrate by two oxidization; the latter contains three reactions by N-methylation catalyzed with glycine sarcosine N-methyltransferase (GSMT) and sarcosine dimethylglycine N-methyltransferase (SDMT). The genome sequences of 134 halophilic type strains were obtained online in both JGI-IMG and EZBiocloud. Approximate 56.0% of halophilic bacteria and 39.6% of halophilic archaea harbors two genes of choline oxidation. About 9.7% of halophilic bacteria and 0.7% halophilic archaea possess two genes of methylation from glycine. Among them, 8 halophilic bacteria have the genes for both choline oxidation and glycine methylation. The expression of the biosynthesis genes of glycine betaine in model microorgainsms or crops can improve their ability to resist salt torlerence. This unique feature derived from the glycine betaine has attracted scientists’ strongly interest and their emergence in modern biotechnology. In the future, the scientific theory and practical application derived from of the biosynthesis of glycine betaine in halophiles must have a significant impact.