A. Verheul et al., AN ATP-DEPENDENT L-CARNITINE TRANSPORTER IN LISTERIA-MONOCYTOGENES SCOTT-A IS INVOLVED IN OSMOPROTECTION, Journal of bacteriology, 177(11), 1995, pp. 3205-3212
Listeria monocytogenes is a gram-positive, psychrotrophic, food-borne
pathogen which is able to grow in osmotically stressful environments.
Carnitine (beta-hydroxy-L-tau-N-trimethyl aminobutyrate) can contribut
e significantly to growth of L. monocytogenes at high osmolarity (R. R
Beumer, M. C. te Giffel, L. J. Cox, F. M. Rombouts, and T. Abee, Appl
, Environ, Microbiol. 60:1359-1363, 1994). Transport of L-[N-methyl-C-
14] carnitine in L. monocytogenes was shown to be energy dependent. An
alysis of cell extracts revealed that L-carnitine was not further meta
bolized, which supplies evidence for its role as an osmoprotectant in
L. monocytogenes. Uptake of L-carnitine proceeds in the absence of a p
roton motive force and is strongly inhibited in the presence of the ph
osphate analogs vanadate and arsenate. The L-carnitine permease is the
refore most likely driven by ATP. Kinetic analysis of L-carnitine tran
sport in glucose-energized cells revealed the presence of a high-affin
ity uptake system with a K-m of 10 mu M and a maximum rate of transpor
t (V-max) of 48 nmol min(-1) mg of protein(-1), L-[C-14]carnitine tran
sport in L. monocytogenes is significantly inhibited by a 10-fold exce
ss of unlabelled L-carnitine, acetylcarnitine, and tau-butyrobetaine,
whereas L-proline and betaine display, even at a 100-fold excess, only
a weak inhibitory effect, In conclusion, an ATP-dependent L-carnitine
transport system in L. monocytogenes is described, and its possible r
oles in cold adaptation and intracellular growth in mammalian cells ar
e discussed.