Affiliation:
1. Department of Microbiology and Molecular Genetics, The University of Texas-Houston Health Science Center
2. Breast Center and Department of Medicine, Baylor College of Medicine, Houston, Texas
Abstract
ABSTRACT
Two regulatory genes,
acpA
and
atxA
, have been reported to control expression of the
Bacillus anthracis
capsule biosynthesis operon
capBCAD
. The
atxA
gene is located on the virulence plasmid pXO1, while pXO2 carries
acpA
and the
cap
genes.
acpA
has been viewed as the major regulator of the
cap
operon because it is essential for capsule gene expression in a pXO1
−
pXO2
+
strain.
atxA
is essential for toxin gene transcription but has also been implicated in control of the
cap
genes. The molecular functions of the regulatory proteins are unknown. We examined
cap
gene expression in a genetically complete pXO1
+
pXO2
+
strain. Our results indicate that another pXO2 gene,
acpB
(previously called pXO2-53; accession no.
NC002146.1
:49418-50866), has a role in
cap
expression. The predicted amino acid sequence of AcpB is 62% similar to that of AcpA and 50% similar to that of AtxA. Assessment of
cap
gene transcription revealed that
cap
expression was not affected in a pXO1
+
pXO2
+
acpB
-null mutant and was slightly reduced in an isogenic
acpA
mutant. However,
cap
gene expression was abolished in an
acpA acpB
double mutant. Microscopic examination of capsule synthesis by the mutants corroborated these findings.
acpA
and
acpB
expression is controlled by
atxA
; capsule synthesis and transcription of
acpA
and
acpB
were markedly reduced in an
atxA
mutant. The data suggest that, in a strain containing both virulence plasmids,
atxA
is the major regulator of capsule synthesis and controls
capBCAD
expression indirectly, via positive regulation of
acpA
and
acpB
.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
Cited by
86 articles.
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