Synthesis of glycine betaine from choline in the moderate halophile Halobacillus halophilus: co-regulation of two divergent, polycistronic operons

The moderately halophilic bacterium Halobacillus halophilus can synthesize glycine betaine from choline. Oxidation of choline is induced by salinity and repressed by exogenous glycine betaine. The genes encoding the choline dehydrogenase (gbsB) and the glycine betaine aldehyde dehydrogenase (gbsA) were identified and shown to constitute an operon. Divergent to this operon is another operon containing gbsR and gbsU that encode proteins with similarities to a transcriptional regulator and a glycine betaine-binding protein respectively. Synthesis of the four Gbs proteins was strictly dependent on the choline concentration of the medium. Salinity was essential for the production of GbsB and increased the production of GbsA, GbsR and GbsU. Glycine betaine repressed the production of all four Gbs proteins with half maximal inhibition at 0.1 mM glycine betaine.