Iron Regulates Expression of Bacillus cereus Hemolysin II via Global Regulator Fur

Abstract

The capacity of pathogens to respond to environmental signals, such as iron concentration, is key to bacterial survival and establishment of a successful infection. Bacillus cereus is a widely distributed bacterium with distinct pathogenic properties. Hemolysin II (HlyII) is one of its pore-forming cytotoxins and has been shown to be involved in bacterial pathogenicity in a number of cell and animal models. Unlike many other B. cereus pathogenicity factors, HlyII is not regulated by pleiotropic transcriptional regulator PlcR but is controlled by its own regulator, HlyIIR. Using a combination of in vivo and in vitro techniques, we show that hlyII expression is also negatively regulated by iron by the global regulator Fur via direct interaction with the hlyII promoter. DNase I footprinting and in vitro transcription experiments indicate that Fur prevents RNA polymerase binding to the hlyII promoter. HlyII expression profiles demonstrate that both HlyIIR and Fur regulate HlyII expression in a concerted fashion, with the effect of Fur being maximal in the early stages of bacterial growth. In sum, these results show that Fur serves as a transcriptional repressor for hlyII expression.

Glucose 6P Binds and Activates HlyIIR to Repress Bacillus cereus Haemolysin hlyII Gene Expression

“…It has also been shown that hlyII expression depends on iron via activation of the global regulator Fur [53]. Indeed, a Fur box was found in the promoter region of the hlyII gene [54], and recent data show that Fur binding to this Fur box competes with RNA polymerase binding to the hlyII promoter, thus interfering with hlyII expression in vitro [53]. Sugar and iron are crucial compounds for bacterial multiplication and thus for their capacity to colonize their hosts.…”

Bacillus cereus phospholipases, enterotoxins, and other hemolysins

“…Hly-II is not regulated by the pleiotropic transcriptional regulator PlcR but is controlled by two negative regulators, HlyIIR and Fur [107,108]. Glucose 6P binds and activates HlyIIR (Guillemet et al, 2013), while iron binds and activates Fur [108], to repress B. cereus hemolysin hlyII gene expression.…”

“…Glucose 6P binds and activates HlyIIR (Guillemet et al, 2013), while iron binds and activates Fur [108], to repress B. cereus hemolysin hlyII gene expression. Therefore, so long as glucose and iron is abundant in the bacterial environment, hlyII will not be expressed.…”

Effect of Bacillus cereus hemolysin II on hepatocyte cells

“…Instead, it was shown that the hemolysin gene is negatively regulated by its own tran scriptional regulator HlyIIR [23,24] and the master regulator Fur [25,26]. The genes for hlyII and hlyIIR are localized in the same chromosomal locus (Bc 3523 and Bc 3522, respectively, in the ATCC 14579 strain) but are not included in the same operon.…”

“…Implemen tation of in vivo and in vitro methodologies allowed us to demonstrate that hlyII gene expression is also neg atively regulated by iron through a direct interaction of the Fur master regulator with a region of DNA overly ing the starting point of transcription [25]. During an increase in Fur protein synthesis, hlyII gene expres sion is reduced because of the competition between the Fur protein and RNA polymerase for the landing site on the DNA [26]. The overall efficiency of hlyII gene expression depends on the modulation of its reg ulation by HlyIIR, as well as by the Fur protein.…”