Abstract
BackgroundMFN1032 is a clinical Pseudomonas fluorescens strain able to grow at 37°C. MFN1032 cells induce necrosis and apoptosis in rat glial cells at this temperature. This strain displays secretion-mediated hemolytic activity involving phospholipase C and cyclolipopeptides. Under laboratory conditions, this activity is not expressed at 37°C. This activity is tightly regulated and is subject to phase variation.ResultsWe found that MFN1032 displays a cell-associated hemolytic activity distinct from the secreted hemolytic activity. Cell-associated hemolysis was expressed at 37°C and was only detected in vitro in mid log growth phase in the presence of erythrocytes. We studied the regulation of this activity in the wild-type strain and in a mutant defective in the Gac two-component pathway. GacS/GacA is a negative regulator of this activity. In contrast to the Pseudomonas fluorescens strains PfO-1 and Pf5, whose genomes have been sequenced, the MFN1032 strain has the type III secretion-like genes hrcRST belonging to the hrpU operon. We showed that disruption of this operon abolished cell-associated hemolytic activity. This activity was not detected in P.fluorescens strains carrying similar hrc genes, as for the P. fluorescens psychrotrophic strain MF37.ConclusionsTo our knowledge this the first demonstration of cell-associated hemolytic activity of a clinical strain of Pseudomonas fluorescens. Moreover, this activity seems to be related to a functional hrpU operon and is independent of biosurfactant production. Precise link between a functional hrpU operon and cell-associated hemolytic activity remains to be elucidated.
Highlights
MFN1032 is a clinical Pseudomonas fluorescens strain able to grow at 37°C
We recently demonstrated that the clinical strain MFN1032 is a Pseudomonas fluorescens sensus stricto Biovar1 strain able to grow at 37°C [10]
This strain has hemolytic activity mediated by secreted factors, similar to the hemolytic activity seen for the opportunistic pathogen Pseudomonas aeruginosa, involving phospholipase C (PlcC) and biosurfactant [11]
Summary
MFN1032 cells induce necrosis and apoptosis in rat glial cells at this temperature This strain displays secretion-mediated hemolytic activity involving phospholipase C and cyclolipopeptides. Under laboratory conditions, this activity is not expressed at 37°C. We recently demonstrated that the clinical strain MFN1032 is a Pseudomonas fluorescens sensus stricto Biovar strain able to grow at 37°C [10]. This strain has hemolytic activity mediated by secreted factors, similar to the hemolytic activity seen for the opportunistic pathogen Pseudomonas aeruginosa, involving phospholipase C (PlcC) and biosurfactant [11]. Spontaneous mutations of the genes encoding the two-component regulatory system GacS/GacA have been identified as the cause
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