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Requirement for FlhA in flagella assembly and swarm-cell differentiation by Proteus mirabilis
D Gygi1, M J Bailey, C Allison
1Cambridge University Department of Pathology, UK.
Abstract:
Swarming by Proteus mirabilis is characterized by cycles of rapid population migration across surfaces, following differentiation of typical rods into long, aseptate swarm cells that overexpress flagella and virulence factors, particularly haemolysin. A non-swarming Tn5phoA mutant was unable to synthesize flagella, to fully elongate or to induce high levels of the toxin. The mutation lay within a 2091 bp gene encoding a homologue of the Escherichia coli FlhA belonging to a family of proteins that are required for assembly of flagella or virulence proteins and that are suggested to act either directly in membrane translocation and/or in regulating synthesis of the export apparatus. In trans expression of multicopy flhA restored cell elongation and migration and generated differentiation-specific hyperexpression of flagellin and toxin genes to levels above those seen in the wild-type strain. Transcription of flhA was strongly induced during differentiation, from its own putative sigma 28 promoter. The results suggest a mechanistic coupling of flagella assembly and swarm-cell differentiation.
Insights
Proteus mirabilis swarming involves cell differentiation into swarm cells that overexpress flagella and toxins. A mutation in the flhA gene disrupted this process, highlighting its role in coordinating flagellar assembly and bacterial differentiation.
Area of Science:
- Microbiology
- Bacterial Physiology
- Molecular Biology
Background:
- Swarming by Proteus mirabilis involves complex cell differentiation into elongated swarm cells.
- These swarm cells exhibit overexpression of flagella and virulence factors, notably haemolysin.
- Understanding the genetic regulation of swarming is crucial for deciphering bacterial motility and pathogenesis.
Purpose of the Study:
- To investigate the genetic basis of Proteus mirabilis swarming and cell differentiation.
- To identify the specific gene responsible for regulating flagellar synthesis and toxin production during swarming.
- To elucidate the role of the identified gene in coordinating flagellar assembly and swarm cell differentiation.
Main Methods:
- Construction and characterization of a non-swarming Tn5phoA mutant of Proteus mirabilis.
- Complementation analysis using in trans expression of the wild-type flhA gene.
- Analysis of gene transcription and protein expression, including flagellin and haemolysin.
- Bioinformatic analysis to identify homologous genes and regulatory elements.
Main Results:
- A Tn5phoA mutant defective in swarming, flagellar synthesis, cell elongation, and toxin production was identified.
- The mutation was localized to a gene encoding a homologue of Escherichia coli FlhA, a protein involved in flagellar and virulence protein export.
- Complementation with multicopy flhA restored swarming, cell elongation, migration, and hyperexpression of flagellin and toxin genes.
- Transcription of flhA was found to be induced during differentiation, regulated by a putative sigma 28 promoter.
Conclusions:
- The flhA gene product plays a critical role in regulating flagellar assembly and virulence factor production during Proteus mirabilis swarming.
- A mechanistic coupling exists between flagellar assembly machinery and the differentiation process leading to swarm cell formation.
- The findings provide insights into the coordinated regulation of bacterial motility and virulence in response to environmental cues.