Role and regulation of ferritin-like proteins in iron homeostasis and oxidative stress survival of Caulobacter crescentus

Abstract

Iron is an essential nutrient that is poorly available to living organisms but can be harmful when in excess due to the production of reactive oxygen species. Bacteria and other organisms use iron storage proteins called ferritins to avoid iron toxicity and as a safe iron source in the cytosol. The alpha-proteobacterium Caulobacter crescentus has two putative ferritins, Bfr and Dps, and some other proteins belonging to the ferritin-like superfamily, among them the one encoded by CC_0557. In this work, we have analyzed the role and regulation of these three putative ferritin-like proteins. Using lacZ-transcriptional fusions, we found that bfr expression is positively regulated (2.5-fold induction) by the Fe-responsive regulator Fur in iron sufficiency, as expected for an iron storage protein. Expression of dps was induced 1.5-fold in iron limitation in a Fur-independent manner, while the expression of the product of CC_0557 was unaffected by either iron supply or Fur. With respect to growth phase, while bfr expression was constant during growth, expression of dps (1.4-fold) and CC_0557 (around seven times) increased in the transition from exponential to stationary phase. Deletion mutant strains for each gene and a double dps/bfr mutant were obtained and tested for oxidative stress resistance. The dps mutant was very sensitive to H2O2, and this phenotype was not relieved by the addition of the iron chelator 2',2-dipyridyl in the conditions tested. While bfr and CC_0557 showed no phenotype as to H2O2 resistance, the double dps/bfr mutant had a similar phenotype to the dps mutation alone. These findings indicate that in C. crescentus Bfr contributes to iron homeostasis and Dps has a role in protection against oxidative stress. The role of the protein CC_0557 containing a ferritin-like fold remains unclear.

Gene network analysis identifies a central post-transcriptional regulator of cellular stress survival

“…The survival phenotypes associated with subtle fold changes in KatG expression suggest that the capacity of KatG to detoxify endogenous sources of H 2 O 2 is at or near its limit under normal cultivation conditions, similar to what has been postulated for E. coli (Imlay, 2013). Expression of the ferritin-like protein, Dps, is controlled by σ T and is reported to aid in the survival of Caulobacter under peroxide stress (de Castro Ferreira et al, 2016). The protective effect of Dps is apparently minimal under our conditions given that a) the peroxide survival defect of ∆sigT is rescued by simply restoring gsrN transcription ( Figure 2B and 2C), and b) survival after peroxide exposure is determined almost entirely by modifying base-pairing interactions between GsrN and katG mRNA.…”

Gene network analysis identifies a central post-transcriptional regulator of cellular stress survival

“…Expression of the ferritin-like protein, Dps, is controlled by σ T and is reported to aid in the survival of Caulobacter under peroxide stress ( de Castro Ferreira et al, 2016 ). The protective effect of Dps is apparently minimal under our conditions given that a) the peroxide survival defect of ∆ sigT is rescued by simply restoring gsrN transcription ( Figure 2B,C ), and b) survival after peroxide exposure is determined almost entirely by modifying base-pairing interactions between GsrN and katG mRNA.…”

Iron Deficiency Generates Oxidative Stress and Activation of the SOS Response in Caulobacter crescentus

“…In E. coli Dps confers protection against oxidative stress caused by H 2 O 2 , and it was proposed that this is due its ability to bind DNA and inhibit the Fenton reaction. In C. crescentus , dps is regulated by SigT (Lourenço et al, 2011) and Dps has an important role in protecting the cell from oxidative stress (de Castro Ferreira et al, 2016). However, while in E. coli dps is induced by starvation and regulated by OxyR under oxidative stress (Almiron et al, 1992; Altuvia et al, 1994), in C. crescentus its regulation is not responsive to hydrogen peroxide, and is independent of Fur and OxyR (de Castro Ferreira et al, 2016).…”