Affiliation:
1. Department of Medical Microbiology & Immunology, University of Wisconsin—Madison, 1300 University Ave., Room 481 MSC, Madison, Wisconsin 53706
Abstract
ABSTRACT
d
-Serine is an amino acid present in mammalian urine that is inhibitory to
Escherichia coli
strains lacking a functional
dsdA
gene. Counterintuitively, a
dsdA
strain of
E. coli
clinical isolate CFT073 hypercolonizes the bladder and kidneys of mice relative to wild type during a coinfection in the murine model of urinary tract infection. We are interested in the mechanisms for uptake of
d
-serine in CFT073.
d
-Serine enters
E. coli
K-12 via CycA, the
d
-alanine transporter and
d
-cycloserine sensitivity locus. CFT073
cycA
can grow on minimal medium with
d
-serine as a sole carbon source. The
dsdX
gene of the
dsdCXA
locus is a likely candidate for an additional
d
-serine transporter based on its predicted amino acid sequence similarity to gluconate transporters. In minimal medium, CFT073
dsdX
can grow on
d
-serine as a sole carbon source; however, CFT073
dsdX cycA
cannot. Additionally, CFT073
dsdXA cycA
is not sensitive to inhibitory concentrations of
d
-serine during growth on glycerol and
d
-serine minimal medium.
d
-[
14
C]serine uptake experiments with CFT073
dsdX cycA
harboring
dsdX
or
cycA
recombinant plasmids confirm that
d
-serine is able to enter
E. coli
cells via CycA or DsdX. In whole-cell
d
-[
14
C]serine uptake experiments, DsdX has an apparent
K
m
of 58.75 μM and a
V
max
of 75.96 nmol/min/mg, and CycA has an apparent
K
m
of 82.40 μM and a
V
max
of 58.90 nmol/min/mg. Only
d
-threonine marginally inhibits DsdX-mediated
d
-serine transport, whereas
d
-alanine, glycine, and
d
-cycloserine inhibit CycA-mediated
d
-serine transport. DsdX or CycA is sufficient to transport physiological quantities of
d
-serine, but DsdX is a
d
-serine-specific permease.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
Cited by
31 articles.
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