Genes for the synthesis of the osmoprotectant glycine betaine from cholinein the moderately halophilic bacterium Halomonas elongata DSM 3043

The genes involved in the oxidative pathway of choline to glycine betaine i n the moderate halophile Halomonas elongata DSM 3043 were isolated by funct ional complementation of an Escherichia coli strain defective in glycine be taine synthesis. The cloned region was able to mediate the oxidation of cho line to glycine betaine in E. coil, but not the transport of choline, indic ating that the gene(s) involved in choline transport are not clustered with the glycine betaine synthesis genes. Nucleotide sequence analysis of a 4.6 kb segment from the cloned DNA revealed the occurrence of three ORFs (betI BA) apparently arranged in an operon. The deduced betI gene product exhibit ed features typical for DNA-binding regulatory proteins. The deduced Bets a nd BetA proteins showed significant similarity to soluble glycine betaine a ldehyde dehydrogenases and membrane-bound choline dehydrogenases, respectiv ely, from a variety of organisms. Evidence is presented that BetA is able t o oxidize both choline and glycine betaine aldehyde and therefore can media te both steps in the synthesis of glycine betaine.