POSTERS - BLAST X - University of Utah
POSTERS - BLAST X - University of Utah
POSTERS - BLAST X - University of Utah
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<strong>BLAST</strong> X Poster #20<br />
THE ROLE OF QUORUM SENSING IN THE CONTROL OF MOTILITY AND PLANT INVASION<br />
BY SINORHIZOBIUM MELILOTI<br />
Nataliya Gurich* and Juan E. González<br />
Department <strong>of</strong> Molecular and Cell Biology, <strong>University</strong> <strong>of</strong> Texas at Dallas, Richardson, Texas,<br />
USA<br />
Quorum sensing, a population density dependent regulation <strong>of</strong> gene expression, is used<br />
by various bacteria to establish symbiotic or pathogenic bacterium-host associations. This<br />
mechanism requires the production <strong>of</strong> signaling molecules called autoinducers. At high cell<br />
population densities, autoinducer concentration in the surrounding area reaches a threshold<br />
level, which leads to activation <strong>of</strong> specific transcriptional regulators and the control <strong>of</strong> numerous<br />
phenotypes.<br />
Sinorhizobium meliloti is a gram-negative soil bacterium that can form a nitrogen-fixing<br />
symbiotic association with its host Medicago sativa. The quorum sensing system in S. meliloti is<br />
comprised <strong>of</strong> a transcriptional regulator, SinR and an autoinducer synthase, SinI, which<br />
specifies production <strong>of</strong> N-acyl homoserine lactone (AHL) signaling molecules. In conjunction<br />
with AHL, an additional regulator, ExpR, controls expression <strong>of</strong> several hundred genes. Recent<br />
microarray studies in our laboratory described the control <strong>of</strong> motility and chemotaxis in S.<br />
meliloti by quorum sensing through the regulators VisN/VisR and Rem in a population-densitydependent<br />
manner. The wild type strain is motile during the early log phase <strong>of</strong> growth but shuts<br />
down flagella synthesis genes during the mid- and late log phases. In contrast, the sinI mutant<br />
remains motile throughout all phases <strong>of</strong> growth, and at the late log phase, 35 motility and<br />
chemotaxis genes are upregulated when compared to wild type.<br />
This inability to repress flagella production by the sinI mutant leads to severe invasion<br />
deficiency. Detailed analysis <strong>of</strong> microarray results suggested that the inability <strong>of</strong> the sinI mutant<br />
to shut down flagella synthesis might be detrimental to successful plant invasion. Mutation <strong>of</strong><br />
flagella synthesis in the sinI strain restored invasion efficiency to wild type levels. Therefore,<br />
control <strong>of</strong> motility and chemotaxis by the ExpR/Sin quorum sensing system plays an important<br />
role in plant invasion and may provide a competitive edge for strains possessing it.<br />
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