Cell-associated hemolysis activity in the clinical strain of Pseudomonas fluorescens MFN1032

Abstract

Abstract Background MFN1032 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. Results We 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 hrc RST 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. Conclusions To 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.