Cell-cell signaling coordinates endophytic lifestyle of Xylella fastidiosa
S. E. LINDOW (1). (1) University of California, Berkeley, CA, U.S.A.
The bacterium <i>Xylella fastidiosa</i>, while capable of causing diseases to important plants such as grape and citrus also commonly occurs as an endophyte in symptomless plant species. Even in host plants most cells occur in small numbers in the xylem vessels that it colonizes and it exhibits strong cell density-dependent behaviors that tend to self-limit its population size in plants, presumably to avoid the cell death that is associated with the plugging of vessels due to bacterial over-growth. <i>X. fastidiosa</i> employs a quorum sensing system that utilizes fatty acid signal molecules that increase in local concentration in proportion to cell numbers in a vessel to suppress the production of type IV pili enabling twitching motility and extracellular enzymes that enable transit between xylem vessels and also contribute to cell multiplication by liberating consumable carbon sources, while enhancing expression fimbrial and afimbrial adhesins that restrict movement within the plant, but which are required for acquisition by, and hence transmission to, new host by insect vectors. <i>X. fastidiosa</i> might thus be considered a common endophyte whose growth and movement in certain host plants is not efficiently repressed at high cell densities.
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