Identification and characterization of an ATP binding cassette L-carnitinetransporter in Listeria monocytogenes

We identified an operon in Listeria monocytogenes EGD with high levels of s equence similarity to the operons encoding the OpuC and OpuB compatible sol ute transporters from Bacillus subtilis, which are members of the ATP bindi ng cassette (ABC) substrate binding protein-dependent transporter superfami ly. The operon, designated opuC, consists of four genes which are predicted to encode an ATP binding protein (OpuCA), an extracellular substrate bindi ng protein (OpuCC), and two membrane-associated proteins presumed to form t he permease (OpuCB and OpuCD). The operon is preceded by a potential SigB-d ependent promoter, hn opuC-defective mutant was generated by the insertiona l inactivation of the opuCA gene. The mutant was impaired for growth at hig h osmolarity in brain heart infusion broth and failed to grow in a defined medium. Supplementation of the defined medium with peptone restored the gro wth of the mutant in this medium. The mutant was found to accumulate the co mpatible solutes glycine betaine and choline to same extent as the parent s train but was defective in the uptake of L-carnitine. We conclude that the opuC operon in L. monocytogenes encodes an ABC compatible solute transporte r which is capable of transporting L-carnitine and which plays an important role in osmoregulation in this pathogen.