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Journal of Bacteriology, October 2000, p. 5513-5520, Vol. 182, No. 19
Department of Microbiology, University of
Iowa, Iowa City, Iowa 52242-1109
Received 11 April 2000/Accepted 20 June 2000
Vibrio parahaemolyticus is a ubiquitous, gram-negative
marine bacterium that undergoes phase variation between opaque and translucent colony morphologies. The purpose of this study was to
determine the factor(s) responsible for the opaque and translucent phenotypes and to examine cell organization within both colony types.
Examination of thin sections of ruthenium red-stained bacterial cells
by electron microscopy revealed a thick, electron-dense layer
surrounding the opaque cells that was absent in preparations from
translucent strains. Extracellular polysaccharide (EPS) material was
extracted from both opaque and translucent strains, and the opaque
strain was shown to produce abundant levels of polysaccharide, in
contrast to the translucent strain. Compositional analysis of the EPS
identified four major sugars: glucose, galactose, fucose, and
N-acetylglucosamine. Confocal scanning laser microscopy was used to investigate cell organization within opaque and translucent colonies. Cells within both types of colonies exhibited striking organization; rod-shaped cells were aligned parallel to one another and
perpendicular to the agar surface throughout the depth of the colony.
Cells within translucent colonies appeared more tightly packed than
cells in opaque colonies. In addition, a dramatic difference in the
structural integrity of these two colony types was observed. When
colonies were perturbed, the cell organization of the translucent
colonies was completely disrupted while the organization of the opaque
colonies was maintained. To our knowledge, this study represents the
first description of how cells are organized in the interior of a
viable bacterial colony. We propose that the copious amount of EPS
produced by the opaque strain fills the intercellular space within the
colony, resulting in increased structural integrity and the opaque phenotype.
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Relation of Capsular Polysaccharide Production and
Colonial Cell Organization to Colony Morphology in Vibrio
parahaemolyticus
*
Corresponding author. Mailing address: Department of
Microbiology, University of Iowa, Iowa City, IA 52242-1109. Phone:
(319) 335-9721. Fax: (319) 335-7679. E-mail:
linda-mccarter{at}uiowa.edu.
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