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J. Bacteriol., Jun 1995, 3205-3212, Vol 177, No. 11
A Verheul, FM Rombouts, RR Beumer and T Abee
Listeria monocytogenes is a gram-positive, psychotrophic, food-borne
pathogen which is able to grow in osmotically stressful environments.
Carnitine (beta-hydroxy-L-tau-N-trimethyl aminobutyrate) can contribute
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-
14C]carnitine in L. monocytogenes was shown to be energy dependent.
Analysis of cell extracts revealed that L-carnitine was not further
metabolized, which supplies evidence for its role as an osmoprotectant in
L. monocytogenes. Uptake of L-carnitine proceeds in the absence of a proton
motive force and is strongly inhibited in the presence of the phosphate
analogs vanadate and arsenate. The L-carnitine permease is therefore most
likely driven by ATP. Kinetic analysis of L-carnitine transport in
glucose-energized cells revealed the presence of a high- affinity uptake
system with a Km of 10 microM and a maximum rate of transport (Vmax) of 48
nmol min-1 mg of protein-1. L-[14C]carnitine transport in L. monocytogenes
is significantly inhibited by a 10-fold excess 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 roles in cold adaptation and
intracellular growth in mammalian cells are discussed.
Copyright © 1995, American Society for Microbiology
An ATP-dependent L-carnitine transporter in Listeria monocytogenes Scott A is involved in osmoprotection
Department of Food Science, Agricultural University Wageningen, The Netherlands.
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