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The Lon protease regulates swarming motility and virulence gene expression in Proteus mirabilis

Katy M Clemmer1, Philip N Rather2,1

  • 1Research Service, Veterans Affairs Medical Center, Decatur, GA, USA.

Journal of Medical Microbiology
|July 17, 2008
PubMed

Insights

A mutation in the Lon protease gene enhances swarming in Proteus mirabilis by increasing flagellar gene expression and protein stability. This Lon protease mutation also boosts virulence gene expression during swarmer cell differentiation.

Area of Science:

  • Microbiology
  • Bacterial Physiology
  • Molecular Biology

Background:

  • Proteus mirabilis swarming is a complex multicellular behavior regulated by various genetic factors.
  • The Lon protease is a conserved ATP-dependent protease involved in protein quality control and stress response in bacteria.

Purpose of the Study:

  • To investigate the role of the Lon protease in the regulation of Proteus mirabilis swarming motility.
  • To elucidate the molecular mechanisms by which Lon protease affects swarmer cell differentiation and virulence gene expression.

Main Methods:

  • Genetic manipulation using mini-Tn5lacZ1 transposon mutagenesis to create lon mutants.
  • Quantitative analysis of mRNA accumulation for key flagellar genes (class 1, 2, and 3).
  • Assessment of FlhD protein stability and expression of lon::lacZ fusion.
  • Phenotypic analysis in liquid and solid media, including cell morphology and flagellin overexpression.
  • Evaluation of virulence gene (hpmBA and zapA) expression during swarmer cell differentiation.

Main Results:

  • A lon protease mutation in Proteus mirabilis resulted in a hyper-swarming phenotype.
  • The lon mutation led to increased mRNA levels of class 1 (flhDC), class 2 (fliA), and class 3 (flaA) flagellar genes.
  • FlhD protein stability was significantly enhanced in the lon mutant background.
  • Expression of a lon::lacZ fusion increased during the swarming cycle, peaking post-differentiation.
  • In liquid media, lon mutants exhibited motility, elongation, and flagellin overexpression.
  • The lon mutation increased the expression of virulence genes hpmBA and zapA during swarmer cell differentiation.

Conclusions:

  • The Lon protease plays a crucial regulatory role in Proteus mirabilis swarming motility and swarmer cell differentiation.
  • Lon protease influences swarming by modulating the expression and stability of key flagellar genes and proteins.
  • The lon mutation impacts bacterial virulence by upregulating specific virulence factors during the swarming cycle.

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