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Evidence that putrescine acts as an extracellular signal required for swarming in Proteus mirabilis
Author(s) -
Sturgill Gwen,
Rather Philip N.
Publication year - 2004
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1046/j.1365-2958.2003.03835.x
Subject(s) - biology , mutant , swarming (honey bee) , proteus mirabilis , psychological repression , swarming motility , extracellular , microbiology and biotechnology , lac operon , motility , genetics , gene , gene expression , virulence , escherichia coli , quorum sensing
Summary In a search for Proteus mirabilis genes that were regulated by cell‐to‐cell signalling, a lacZ fusion ( cmr437:: mini‐Tn 5lacZ ) was identified that was repressed 10‐fold by a self‐produced extracellular signal from wild‐type cells. However, the cmr437 ::mini‐Tn 5lacZ insertion itself led to a marked reduction in this extracellular repressing signal. The cmr437 ::mini‐Tn 5lacZ insertion was mapped to a speA homologue in P. mirabilis. Sequence analysis indicated that a speB homologue was encoded downstream of speA . Products of the SpeA and SpeB enzymes (agmatine and putrescine) were tested for repression of cmr437::lacZ . Agmatine did not have repressing activity. However, putrescine was an effective repressing molecule at concentrations down to 30 µM. A second prominent phenotype of the cmr437 ( speA )::mini‐Tn 5lacZ insertion was a severe defect in swarming motility. This swarming defect was also observed in a strain containing a disruption of the downstream speB gene. Differentiation of the speB mutant to swarmer cells was delayed by two hours relative to wild‐type cells. Furthermore, the speB mutant was unable to migrate effectively across agar surfaces and formed very closely spaced swarming rings. Exogenous putrescine restored both the normal timing of swarmer cell differentiation and the ability to migrate to speB mutants.