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

Abstract

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.

Genetic Control of Osmoadaptive Glycine Betaine Synthesis in Bacillus subtilis through the Choline-Sensing and Glycine Betaine-Responsive GbsR Repressor

“…Our database searches and computer predictions suggest that it is a regulatory protein carrying a winged-helix DNA-binding motif (20,33) between amino acids 49 and 73 (see below). YuaC-related proteins are encoded by genes found in close vicinity of functionally characterized glycine betaine biosynthetic genes from Staphylococcus xylosus (51), Halobacillus dabanensis (23), and Halobacillus halophilus (15). We therefore considered the possibility that the B. subtilis YuaC protein might function as a transcriptional regulator for the gbsAB operon.…”

“…Our database searches showed that the cudTCAB gene cluster is present in every sequenced Staphylococcus genome, suggesting that CudC/GbsRtype proteins function widely as the regulatory protein for glycine betaine synthesis in staphylococci. In the functionally characterized glycine betaine biosynthetic gene clusters of Halobacillus dabanensis (23) and Halobacillus halophilus (15), gbsR-type genes are present as well and are divergently orientated from the gbsAB genes and cotranscribed with a gene (referred to as gbsT and gbsU, respectively) encoding an orphan ligand-binding protein that bears the hallmarks of a substrate-binding protein associated with ABC transport system possessing a specificity for glycine betaine or other osmoprotectants with a trimethylammonium or a dimethlysulfonium head group (47,52,53,58). Burkhardt et al (15) demonstrated the induction of the transcription of the H. halophilus gbsAB and gbsRU gene clusters in response to choline availability and their repression by glycine betaine but did not experimentally correlate these transcriptional responses with the gbsR-encoded protein.…”

“…Microorganisms can synthesize glycine betaine by one of two different routes: (i) through a stepwise methylation of the amino acid glycine (39,46,59) or (ii) through the import and subsequent oxidation of choline using various combinations of enzymes (5,15,42,49,51). B. subtilis uses this latter route to produce glycine betaine and imports for this purpose the precursor choline into the cell via two osmotically inducible ABC-type transport systems: the aforementioned OpuC transporter and the OpuB system ( Fig.…”

Phylogenetic analysis of substrate-binding subunits in an osmoprotectant system

“…Because of the need to capture nutrients at the beginning of the diversification of this and other systems, organisms that could directly capture glycine betaine had an advantage over those that could only capture choline from which glycine betaine could be synthesized. This advantage can be explained by the fact that transporting glycine betaine is more energetically advantageous, since it makes it unnecessary for the organism to synthesize the two enzymes and perform the two chemical reactions necessary for the catabolism of choline and glycine betaine (Burkhardt et al, 2009) (Figure 9). This gain in terms of energy efficiency must have been fundamental to the successful establishment of glycine betaine transport and the sharing of this transport system among various prokaryotes.…”

“…This is an important molecule for the biosynthesis of membrane phospholipids (Aktas et al, 2010) and acts as a precursor of glycine betaine (Burkhardt et al, 2009) and participates in metabolic pathways for the synthesis of amino acids such as methionine (Barra et al, 2006). This system has been modified over time, allowing transport of a variety of molecules; furthermore, it has been structurally modified so that it now has morphological diversity, making it very interesting with regard to its SBPs.…”