Evidence that putrescine acts as an extracellular signal required for swarming in Proteus mirabilis

Speaker: 張力云                           Time: PM3:00-4:00; 4/28/2004

Commentator: 吳俊忠 老師                  Place: 601

Abstract

In bacteria, cellular communication with each other is important for many cellular function and gene regulation. Proteus mirabilis, a common urinary tract pathogen of humans, is best known for its ability to multicellular migration termed swarming (1). Swarming is likely to be regulated by cell- to-cell signal (2). In this paper, the author used a mini-Tn5lacZ reporter transposon to generate a bank of random mutants. From this mutant bank, they identified a mutant whose LacZ expression level was repressed by the extracellular signaling molecule produced by a wild type P. mirabilis. The amount of signal produced by this mutant was also found to be remarkably reduced. Sequence analysis showed that the transposon was inserted into a speA homologue (speA::lacZ) in this mutant. The speA gene of E. coli encodes an arginine decarboxylase converting L- arginine to agmatine. Addition of agmatine to the speA::lacZ mutant did not repress the LacZ expression, but addition of putrescine did. This was due to a polar effect of speA::lacZ mutant on the downstream gene, speB, which converted agmatine to putrescine. The author further found that either thespeA:: lacZ mutant or disruption of speB by a suicide plasmid exhibited reduced swarming ability. The defective swarming of the speB mutant was because the time of cell differentiation was delayed and migration rate was lowered, but not due to reduced growth rate or flagellar function. In the presence of putrescine, the time-course of cell differentiation and migration rate of the speBmutant were similar to the wild-type strain and its swarming activity was restored. These results demonstrate that putrescine is an important singaling molecule for swarming of Proteus mirabilis.

References

1. Mobley, H.L.T., and Belas, R. (1995) Swarming and pathogenicity of Proteus mirabilis in the urinary tract. Trends Microbiol 3: 280-284.

2. Miller, M.B., and Bassler, B.L. (2001) Quorum sensing in bacteria. Annu Rev Microbiol 55: 165-199.

3. Sturgill, G.., and Rather, Philip N. (2004) Evidence that putrescine acts as an extracellular signal required for swarming in Proteus mirabilis. Molecular Microbiology 51: 437-446.