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J. Bacteriol., 05 1995, 2251-2258, Vol 177, No. 9
DG Cvitkovitch, DA Boyd, T Thevenot and IR Hamilton
Streptococcus mutans transports glucose via the phosphoenolpyruvate
(PEP)-dependent sugar phosphotransferase system (PTS). Earlier studies
indicated that an alternate glucose transport system functions in this
organism under conditions of high growth rates, low pH, or excess glucose.
To identify this system, S. mutans BM71 was transformed with integration
vector pDC-5 to generate a mutant, DC10, defective in the general PTS
protein enzyme I (EI). This mutant expressed a defective EI that had been
truncated by approximately 150 amino acids at the carboxyl terminus as
revealed by Western blot (immunoblot) analysis with anti-EI antibody and
Southern hybridizations with a fragment of the wild-type EI gene as a
probe. Phosphotransfer assays utilizing 32P- PEP indicated that DC10 was
incapable of phosphorylating HPr and EIIAMan, indicating a nonfunctional
PTS. This was confirmed by the fact that DC10 was able to ferment glucose
but not a variety of other PTS substrates and phosphorylated glucose with
ATP and not PEP. Kinetic assays indicated that the non-PTS system exhibited
an apparent Ks of 125 microM for glucose and a Vmax of 0.87 nmol mg (dry
weight) of cells- 1 min-1. Sugar competition experiments with DC10
indicated that the non- PTS transport system had high specificity for
glucose since glucose transport was not significantly by a 100-fold molar
excess of several competing sugar substrates, including 2-deoxyglucose and
alpha- methylglucoside. These results demonstrate that S. mutans possesses
a glucose transport system that can function independently of the PEP PTS.
Copyright © 1995, American Society for Microbiology
Glucose transport by a mutant of Streptococcus mutans unable to accumulate sugars via the phosphoenolpyruvate phosphotransferase system
Department of Oral Biology, Faculty of Dentistry, University of Manitoba, Winnipeg, Canada.
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