Responses of genes for the uptake of glycine betaine in Virgibacillus halodenitrificans PDB-F2 under NaCl stress

The moderately halophilic bacterium, Virgibacillus halodenitrificans PDB-F2, is able to degrade phenol in high-salinity environment, which copes with external salinity fluctuation by biosynthesis or uptake of compatible solutes. Four putative compatible solutes transport systems BetL, OpuD1, OpuD2 and OpuD3, which belong to betaine-carnitine-choline transporters (BCCT) family, have been predicted from the complete genome sequence of V. halodenitrificans PDB-F2. This study investigated the responses of four transport genes betL, opuD1, opuD2 and opuD3 to NaCl stress in V. halodenitrificans PDB-F2. Transcriptional analysis showed that betL, opuD1, opuD2 and opuD3 were induced by NaCl stress, and had specificity for glycine betaine (GB). The maximal induction of four transport genes transcription depended on high salinity plus GB. Exogenous GB afforded effective osmoprotection for V. halodenitrificans PDB-F2 at high salinity, especially at 15% (wt/vol) NaCl. Escherichia coli MHK13 is a mutant strain which is unable to grow at high salt condition. We examined the growth of E. coli MHK13 complemented with each of four transport genes and examined the uptake of GB in cells by 1H nuclear magnetic resonance (1H NMR) spectroscopy under high salt condition. These data showed that all four transporters were able to transport GB.