Affiliation:
1. Department of Microbiology and Immunology, Loyola University Chicago, 2160 S. First Ave., Bldg. 105, Maywood, Illinois 60153
Abstract
ABSTRACT
Flagellar biogenesis and hence motility of
Vibrio fischeri
depends upon the presence of magnesium. In the absence of magnesium, cells contain few or no flagella and are poorly motile or nonmotile. To dissect the mechanism by which this regulation occurs, we screened transposon insertion mutants for those that could migrate through soft agar medium lacking added magnesium. We identified mutants with insertions in two distinct genes, VF0989 and VFA0959, which we termed
mifA
and
mifB
, respectively, for
m
agnesium-dependent
i
nduction of
f
lagellation. Each gene encodes a predicted membrane-associated protein with diguanylate cyclase activity. Consistent with that activity, introduction into
V. fischeri
of medium-copy plasmids carrying these genes inhibited motility. Furthermore, multicopy expression of
mifA
induced other phenotypes known to be correlated with diguanylate cyclase activity, including cellulose biosynthesis and biofilm formation. To directly test their function, we introduced the wild-type genes on high-copy plasmids into
Escherichia coli
. We assayed for the production of cyclic di-GMP using two-dimensional thin-layer chromatography and found that strains carrying these plasmids produced a small but reproducible spot that migrated with an
R
f
value consistent with cyclic di-GMP that was not produced by strains carrying the vector control. Disruptions of
mifA
or
mifB
increased flagellin levels, while multicopy expression decreased them. Semiquantitative reverse transcription-PCR experiments revealed no significant difference in the amount of flagellin transcripts produced in either the presence or absence of Mg
2+
by either vector control or
mifA
-overexpressing cells, indicating that the impact of magnesium and cyclic-di-GMP primarily acts following transcription. Finally, we present a model for the roles of magnesium and cyclic di-GMP in the control of motility of
V. fischeri
.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
Cited by
44 articles.
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