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A cell-surface polysaccharide that facilitates rapid population migration by differentiated swarm cells of Proteus
1University of Cambridge, Department of Pathology, UK.
Abstract:
Swarming by Proteus mirabilis is characterized by cycles of rapid population migration across surfaces, following differentiation of typical vegetative rods into long, hyperflagellated, virulent swarm cells. A swarm-defective TnphoA insertion mutant was isolated that was not defective in cell motility, differentiation or control of the migration cycle, but was specifically impaired in the ability to undergo surface translocation as a multicellular mass. The mutation, previously shown to compromise urinary tract virulence, was located within a 1112 bp gene that restored normal swarming of the mutant when expressed in trans. The gene encoded a 40.6 kDa protein that is related to putative sugar transferases required for lipopolysaccharide (LPS) core modification in Shigella and Salmonella. The immediately distal open reading frame encoded a protein that is related to dehydrogenases involved in the synthesis of LPS O-side-chains, enterobacterial common antigen and extracellular polysaccharide (PS). Gel electrophoresis and electron microscopy showed that the mutant still made LPS but it had lost the ability to assemble a surface (capsular) PS, which gas-liquid chromatography and mass spectrometry indicated to be an acidic type II molecule rich in galacturonic acid and galactosamine. We suggest that this surface PS facilitates translocation of differentiated cell populations by reducing surface friction.
Insights
Proteus mirabilis swarming requires a surface polysaccharide (PS) for multicellular translocation. Loss of this PS impairs bacterial swarming and virulence, highlighting its role in bacterial migration.
Area of Science:
- Microbiology
- Bacterial Pathogenesis
- Biochemistry
Background:
- Swarming by Proteus mirabilis involves differentiation into hyperflagellated swarm cells and coordinated migration.
- A specific mutant exhibited defects in multicellular surface translocation, not motility or differentiation.
Purpose of the Study:
- To identify the genetic basis of the swarming defect in a Proteus mirabilis mutant.
- To characterize the molecular function of the affected gene and its role in surface translocation.
Main Methods:
- Isolation and characterization of a swarm-defective TnphoA mutant.
- Gene cloning and complementation to restore swarming.
- Biochemical analysis (LPS, PS composition) using gel electrophoresis, electron microscopy, GC-MS.
Main Results:
- A mutation in a gene encoding a putative sugar transferase disrupted surface polysaccharide (PS) assembly.
- The mutant produced LPS but lacked a specific acidic capsular PS rich in galacturonic acid and galactosamine.
- This PS is crucial for the multicellular translocation characteristic of Proteus mirabilis swarming.
Conclusions:
- The identified gene is essential for the synthesis of a surface polysaccharide required for Proteus mirabilis swarming.
- This surface PS likely facilitates bacterial migration by reducing surface friction.
- The findings provide insights into the mechanisms of bacterial surface translocation and virulence.