POSTERS - BLAST X - University of Utah

BLAST X Poster #23
THE Cyclic-di-GMP RECEPTOR PROTEIN YcgR LOCALIZES TO THE FLAGELLAR BASAL
BODY AND CHANGES MOTOR BIAS IN SALMONELLA
Vincent Nieto* and Rasika Harshey
Section of Molecular Genetics and Microbiology, University of Texas at Austin, Texas 78712
Cyclic-di-GMP (cdG) is a bacterial second messenger that plays a central role in the
transition between motile and sessile states. In Salmonella enterica, absence of the cdG
phosphodiesterase YhjH is known to elevate cdG levels, inhibit motility, and promote biofilm
formation. YcgR, a cdG -binding protein, is required for this phenomenon. We show in this study
that the absence of YhjH inhibits chemotaxis, and that this inhibition is more pronounced when
YcgR is overexpressed from a plasmid. In liquid media, the bacteria were predominantly smooth
swimming. Tethering experiments showed a pronounced shift to CCW rotation with a significant
slowing of motor rotation. Inhibition of chemotaxis was therefore at the level of either production,
or activity of the chemotaxis response regulator CheY~P, which acts at the switch to change the
default CCW bias to CW. Expression of a GFP-tagged cdG-binding protein YcgR in a yhjH
mutant background, resulted in punctate fluorescent dots along the cell membrane. Presence of
the puncta was dependent on the presence of flagellar basal bodies, but not on presence of
chemotaxis signaling components, suggesting that YcgR inhibits chemotaxis by acting at the
switch. Inhibition of chemotaxis may represent a novel strategy to prepare for a sedentary
existence by disfavoring migration away from a substrate on which a biofilm is to be formed.
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