Role of carnitine in adaptation of Chromohalobacter salexigens DSM 3043 and its mutants to osmotic and temperature stress in defined medium.

L-Carnitine is widespread in nature, but little information is available on its metabolism and physiological functions in moderate halophiles. In this study, we found that Chromohalobacter salexigens DSM 3043 could utilize carnitine not only as a nutrient, but also as an osmolyte. When grown at 37 °C under salt-stress conditions, the strain utilized carnitine as an osmoprotectant by enzymatically converting it into GB. When grown at low and high temperature, both carnitine and its metabolic intermediate GB were simultaneously accumulated intracellularly, serving as cryoprotectants and thermoprotectants. The genes (csal_3172, csal_3173, and csal_3174) which were predicted to participate in L-carnitine degradation to GB were deleted to construct the corresponding mutants. The effects of salinity and temperature on the growth rates and cytoplasmic solute pools of the C. salexigens wild-type and mutant strains were investigated. ¹³C-NMR analysis revealed that GB was still detected in the Δcsal_3172Δcsal_3173Δcsal_3174 mutant grown in a defined medium with added DL-carnitine, but not with L-carnitine, indicating that an unidentified D-carnitine degradation pathway exists in C. salexigens. Taken together, the data presented in this study expand our knowledge on carnitine metabolism and its physiological functions in C. salexigens exposed to single or multiple environmental abiotic stress.