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Cell differentiation of Proteus mirabilis is initiated by glutamine, a specific chemoattractant for swarming cells
Abstract:
Swarming by Proteus mirabilis involves differentiation of typical short vegetative rods into filamentous hyperflagellated swarm cells which undergo cycles of rapid and co-ordinated population migration across surfaces and exhibit high levels of virulence gene expression. By supplementing a minimal growth medium (MGM) unable to support swarming migration we identified a single amino acid, glutamine, as sufficient to signal initiation of cell differentiation and migration. Bacteria isolated from the migrating edge of colonies grown for 8 h with glutamine as the only amino acid were filamentous and synthesized the characteristic high levels of flagellin and haemolysin. In contrast, addition of the other 19 common amino acids (excluding glutamine) individually or in combination did not initiate differentiation even after 24 h, cells remaining typical vegetative rods with basal levels of haemolysin and flagellin. The glutamine analogue gamma-glutamyl hydroxamate (GH) inhibited swarming but not growth of P. mirabilis on glutamine MGM and transposon mutants defective in glutamine uptake retained their response to glutamine signalling and its inhibition by GH, suggesting that differentiation signalling by glutamine may be transduced independently of the cellular glutamine transport system. Levels of mRNA transcribed from the haemolysin (hpmA) and flagellin (fliC) genes were low in vegetative cells grown on MGM without glutamine or with glutamine and GH, but were specifically increased c. 40-fold during glutamine-dependent differentiation. In liquid glutamine-MGM cultures, differentiation to filamentous hyper-flagellated hyper-haemolytic swarm cells occurred early in the exponential phase of growth, and increased concomitantly with the concentration of glutamine from a 0.1 mM threshold up to 10 mM.(ABSTRACT TRUNCATED AT 250 WORDS)
Insights
Glutamine signals Proteus mirabilis to differentiate into swarm cells, initiating migration and virulence gene expression. This amino acid is essential for triggering swarming behavior in this bacterium.
Area of Science:
- Microbiology
- Bacterial Physiology
- Cell Differentiation
Background:
- Proteus mirabilis swarming involves cell differentiation into hyperflagellated swarm cells.
- Swarming cells exhibit coordinated migration and high virulence gene expression.
Purpose of the Study:
- To identify signaling molecules that initiate Proteus mirabilis swarming.
- To understand the role of amino acids in triggering cell differentiation and migration.
Main Methods:
- Supplementing minimal growth medium (MGM) with amino acids.
- Analyzing bacterial morphology, flagellin and haemolysin synthesis.
- Using glutamine analogue (GH) and transposon mutants to study signaling pathways.
Main Results:
- Glutamine alone was sufficient to induce cell differentiation and migration.
- Other amino acids did not trigger swarming.
- Glutamine increased flagellin and haemolysin gene expression by approximately 40-fold.
- Glutamine signaling appears independent of the cellular glutamine transport system.
Conclusions:
- Glutamine is a key signal for initiating Proteus mirabilis swarming.
- The glutamine signaling pathway for differentiation is distinct from its transport system.
- Understanding this pathway can inform strategies to control bacterial swarming and virulence.