POSTERS - BLAST X - University of Utah

BLAST X Tue. Morning Session
STATOR SELECTION IN SHEWANELLA ONEIDENSIS MR-1
Anja Paulick, Andrea Koerdt, Kai M. Thormann
Department of Ecophysiology, MPI für terrestrische Mikrobiologie, Karl-von-Frisch-Strasse, D-
35043 Marburg, Germany
The Gram-negative metal-ion reducing bacterium Shewanella oneidensis MR-1 is motile
by means of a single polar flagellum. We identified two potential stator systems, PomAB and
MotAB, each sufficient as a force generator to drive flagellar rotation. Physiological studies
demonstrate that PomAB is sodium-dependent while MotAB is powered by proton motive force.
Homology comparisons strongly indicate that the MotAB system has been acquired by
horizontal gene transfer, probably as a consequence of long-term adaptation from a marine to a
low-sodium freshwater environment. As in S. oneidensis MR-1, a number of bacterial species
possess more than one stator system to power a single flagellar system but it is yet unclear,
how selection of the stators is achieved.
Expression analysis at the single cell level showed that both stator systems of S.
oneidensis MR-1 are expressed simultaneously, and functional fusions of PomB and MotB to
mCherry revealed that both stator systems are present in the cell at the same time. While the
Pom system is efficiently localizing to the flagellated cell pole under all conditions, the Mot stator
is located in the cell membrane and only found at the cell pole at high abundance in media with
low sodium content. At low sodium, both stator systems are localizing to the flagellated cell pole
in the majority of the cell population, thus indicating that under such conditions a hybrid motor
may be formed. We conclude that stator selection occurs at the level of protein localization by
alterations in the localization efficiency in response to sodium levels.
In Vibrio species, two additional proteins, MotX and MotY, are involved in stator
recruitment and sodium-dependent swimming. We therefore analyzed whether S. oneidensis
MR-1 orthologs to MotX and MotY play a role in stator selection. Mutant and localization
analyses demonstrated that both proteins are required for function of the Pom as well as the
Mot stator system. As opposed to the Vibrio system, in S. oneidensis MR-1, MotX and MotY are
not required for stator recruitment and also do not play a role in stator selection in response to
sodium conditions.
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