Quorum-sensing regulation governs bacterial adhesion, biofilm development, and host colonization in Pantoea stewartii subspecies stewartii

doi:10.1073/pnas.0509860103

Quorum-sensing regulation governs bacterial adhesion, biofilm development, and host colonization in Pantoea stewartii subspecies stewartii

Departments of *Molecular and Cell Biology and
^‡Plant Science, University of Connecticut, Storrs, CT 06269; and
^§Pathogen Functional Genomic Resource Center, Center for Genomic Research, 9712 Medical Drive, Rockville, MD 20850

Edited by Luis Sequeira, University of Wisconsin, Madison, WI, and approved February 2, 2006
↵ ^†M.D.K. and D.T. contributed equally to this work. (received for review November 14, 2005)

Abstract

The phytopathogenic bacterium Pantoea stewartii subsp. stewartii synthesizes stewartan exo/capsular polysaccharide (EPS) in a cell density-dependent manner governed by the EsaI/EsaR quorum-sensing (QS) system. This study analyzes biofilm development and host colonization of the WT and QS regulatory mutant strains of P. stewartii. First, we show that the cell density-dependent synthesis of stewartan EPS, governed by the EsaI/EsaR QS system, is required for proper bacterial adhesion and development of spatially defined, 3D biofilms. Second, a nonvirulent mutant lacking the esaI gene adheres strongly to surfaces and develops densely packed, less structurally defined biofilms in vitro. This strain appears to be arrested in a low cell density developmental mode. Exposure of this strain to exogenous N-acyl-homoserine lactone counteracts this adhesion phenotype. Third, QS mutants lacking the EsaR repressor attach poorly to surfaces and form amorphous biofilms heavily enmeshed in excess EPS. Fourth, the WT strain disseminates efficiently within the xylem, primarily in a basipetal direction. In contrast, the two QS mutant strains remain largely localized at the site of infection. Fifth, and most significantly, epifluorescence microscopic imaging of infected leaf tissue and excised xylem vessels reveals that the bacteria colonize the xylem with unexpected specificity, particularly toward the annular rings and spiral secondary wall thickenings of protoxylem, as opposed to indiscriminate growth to fill the xylem lumen. These observations are significant to bacterial plant pathogenesis in general and may reveal targets for disease control.

Footnotes

^¶To whom correspondence should be addressed at:
Department of Plant Science, University of Connecticut, 302 ABL, 1390 Storrs Road, Storrs, CT 06269-4163.
E-mail: susanne.vonbodman{at}uconn.edu
Author contributions: M.D.K., D.T., and S.B.v.B. designed research; M.D.K., D.T., and T.D.M. performed research; M.D.K. and S.B.v.B. contributed new reagents/analytic tools; M.D.K., D.T., and S.B.v.B. analyzed data; and M.D.K. and S.B.v.B. wrote the paper.
Conflict of interest statement: No conflicts declared.
This paper was submitted directly (Track II) to the PNAS office.
Abbreviations:

Abbreviations:

AHL,

acyl-l-homoserine lactone;

QS,

quorum-sensing;

EPS,

exo/capsular polysaccharide;

CV,

crystal violet.