Deciphering the Role of Multiple Betaine-Carnitine-Choline Transporters in the Halophile Vibrio parahaemolyticus

Vibrio parahaemolyticus is a halophile that is the predominant cause of bacterial seafood-related gastroenteritis worldwide. To survive in the marine environment,V. parahaemolyticus must have adaptive strategies to cope with salinity changes. Six putative compatible solute (CS) transport systems were previously predicted from the genome sequence ofV. parahaemolyticus RIMD2210633. In this study, we determined the role of the four putative betaine-carnitine-choline transporter (BCCT) homologues VP1456, VP1723, VP1905, and VPA0356 in the NaCl stress response. Expression analysis of the four BCCTs subjected to NaCl upshock showed that VP1456, VP1905, and VPA0356, but not VP1723, were induced. We constructed in-frame single-deletion mutant strains for all four BCCTs, all of which behaved similarly to the wild-type strain, demonstrating a redundancy of the systems. Growth analysis of a quadruple mutant and four BCCT triple mutants demonstrated the requirement for at least one BCCT for efficient CS uptake. We complementedEscherichia coli MHK13, a CS synthesis- and transporter-negative strain, with each BCCT and examined CS uptake by growth analysis and1 H nuclear magnetic resonance (NMR) spectroscopy analyses. These data demonstrated that VP1456 had the most diverse substrate transport ability, taking up glycine betaine (GB), proline, choline, and ectoine. VP1456 was the sole ectoine transporter. In addition, the data demonstrated that VP1723 can transport GB, proline, and choline, whereas VP1905 and VPA0356 transported only GB. Overall, the data showed that the BCCTs are functional and that there is redundancy among them.