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Category: Microbial Genetics and Molecular Biology
Swarming Migration by Proteus and Related Bacteria, Page 1 of 2
< Previous page | Next page > /docserver/preview/fulltext/10.1128/9781555818166/9781555811587_Chap19-1.gif /docserver/preview/fulltext/10.1128/9781555818166/9781555811587_Chap19-2.gifAbstract:
This chapter reviews knowledge of bacterial swarming and the likely underlying mechanisms, focusing principally on studies of Proteus mirabilis. Swarming P. mirabilis produces very large spreading colonies in which concentric zonation, or terracing, results from periodic cycles of mass migration interspersed with population growth without expansion of the colony edge. A role for bacterial motility has been demonstrated in a variety of pathogen-host interactions. Histological analysis of renal tissues from mice infected by wild-type P. mirabilis revealed that differentiated cells were the major invasive cell type. The chapter focuses on molecular analysis of swarming differentiation and migration. Environmental attractants or repellents are recognized by transmembrane receptors, the methyl-accepting chemotaxis proteins (MCPs), that transduce signals to the cytoplasmic components of the chemotaxis phosphorelay, CheWAY. The physiological status of P. mirabilis cells affects their ability to swarm, as high growth rates of vegetative cells on nutrient-rich solid medium stimulate differentiation. Cell-cell contact is stabilized by the production of cell-surface polysaccharides that form a slime capsule around groups of P. mirabilis swarm cells. The primary function of FlhDC is the control of flagella biogenesis, but in Escherichia coli, Serratia liquefaciens, and P. mirabilis FlhDC also represses cell division. The hyperexpression of the flagellar gene hierarchy in Proteus has highlighted induction and negative regulation barely evident in undifferentiated cells, and the coupling of swarming to virulence, whether through an intrinsic role in colonization or coregulation of motility and virulence genes, adds an additional level of significance.
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Possible mechanisms of swarming. A simple view of a swarm cell indicating putative underlying mechanisms that have been the foci of study.
Possible mechanisms of swarming. A simple view of a swarm cell indicating putative underlying mechanisms that have been the foci of study.
Swarming on solid growth medium by P. mirabilis. (A) Swarming of P. mirabilis inoculated in the center of a Petri plate containing complex growth medium solidified by 2% agar. V, vegetative cells from the center of the colony; S, part of a hyperflagellated swarm cell from the migrating colony edge. (B) Stages in the swarming cycle of P. mirabilis growing on solid medium. ( From Allison and Hughes, 1991a. )
Swarming on solid growth medium by P. mirabilis. (A) Swarming of P. mirabilis inoculated in the center of a Petri plate containing complex growth medium solidified by 2% agar. V, vegetative cells from the center of the colony; S, part of a hyperflagellated swarm cell from the migrating colony edge. (B) Stages in the swarming cycle of P. mirabilis growing on solid medium. ( From Allison and Hughes, 1991a. )
P. mirabilis swarming-defective mutants. Wild-type P. mirabilis (WT) and transposon mutants, nonmotile nonswarming (NMNS), motile non-swarming (MNS), dendritic swarming (DS), frequent consolidation (FC), and infrequent consolidation (IC), are shown. ( From Allison and Hughes, 1991a. )
P. mirabilis swarming-defective mutants. Wild-type P. mirabilis (WT) and transposon mutants, nonmotile nonswarming (NMNS), motile non-swarming (MNS), dendritic swarming (DS), frequent consolidation (FC), and infrequent consolidation (IC), are shown. ( From Allison and Hughes, 1991a. )
The enterobacterial flagellum. A representation of an enterobacterial flagellum is shown, indicating the protein components of each flagellar substructure. The flagellum crosses both the cytoplasmic membrane (CM) and the outer membrane (OM) and is stabilized in the cell envelope by three ring structures: (i) the MS ring, (ii) the Ρ ring, and (iii) the L ring. The axial substructures of the flagellum, i.e., the rod, the hook, the HAPs, and the filament, make up a helical array of polymerized proteins that form a continuous hollow tube. The substructures involved in generating rotation are associated with the CM at the base of the flagellum. The flagellar export apparatus (shaded) is thought to be loosely associated with the base of the flagellum.
The enterobacterial flagellum. A representation of an enterobacterial flagellum is shown, indicating the protein components of each flagellar substructure. The flagellum crosses both the cytoplasmic membrane (CM) and the outer membrane (OM) and is stabilized in the cell envelope by three ring structures: (i) the MS ring, (ii) the Ρ ring, and (iii) the L ring. The axial substructures of the flagellum, i.e., the rod, the hook, the HAPs, and the filament, make up a helical array of polymerized proteins that form a continuous hollow tube. The substructures involved in generating rotation are associated with the CM at the base of the flagellum. The flagellar export apparatus (shaded) is thought to be loosely associated with the base of the flagellum.
FlhDC, a major assimilatory checkpoint. Summary of the observed relationships between known (CRP, UmoA to D, Lrp, and OmpR) and as yet-uncharacterized (X) regulators of the flagellar gene hierarchy. FlhD and FlhC together serve as a regulatory fulcrum assimilating swarm signals and mediating responses. Negative feedback to P. mirabilis flhDC, umoA, and umoD arises from defects in flagellar assembly and class 2 gene repression by the accumulation of the anti-sigma factor FlgM, which binds the flagellum-specific σ28. Arrows, positive regulation; barred lines, negative regulation.
FlhDC, a major assimilatory checkpoint. Summary of the observed relationships between known (CRP, UmoA to D, Lrp, and OmpR) and as yet-uncharacterized (X) regulators of the flagellar gene hierarchy. FlhD and FlhC together serve as a regulatory fulcrum assimilating swarm signals and mediating responses. Negative feedback to P. mirabilis flhDC, umoA, and umoD arises from defects in flagellar assembly and class 2 gene repression by the accumulation of the anti-sigma factor FlgM, which binds the flagellum-specific σ28. Arrows, positive regulation; barred lines, negative regulation.
Components and factors identified as involved in swarming. Studies of swarming differentiation in gram-negative organisms, including P. mirabilis, have substantiated the early view of swarming portrayed in Fig. 1 .
Components and factors identified as involved in swarming. Studies of swarming differentiation in gram-negative organisms, including P. mirabilis, have substantiated the early view of swarming portrayed in Fig. 1 .