Free Rather Than Total Iron Content Is Critically Linked to the Fur Physiology in Shewanella oneidensis

Abstract

Ferric uptake regulator (Fur) is a transcriptional regulator playing a central role in iron homeostasis of many bacteria, and Fur inactivation commonly results in pleiotropic phenotypes. In Shewanella oneidensis, a representative of dissimilatory metal-reducing γ-proteobacteria capable of respiring a variety of chemicals as electron acceptors (EAs), Fur loss substantially impairs respiration. However, to date the mechanism underlying the physiological phenomenon remains obscure. This investigation reveals that Fur loss compromises activity of iron proteins requiring biosynthetic processes for their iron cofactors, heme in particular. We then show that S. oneidensis Fur is critical for maintaining heme homeostasis by affecting both its biosynthesis and decomposition of the molecule. Intriguingly, the abundance of iron-containing proteins controlled by H2O2-responding regulator OxyR increases in the fur mutant because the Fur loss activates OxyR. By comparing suppression of membrane-impermeable, membrane-permeable, and intracellular-only iron chelators on heme deficiency and elevated H2O2 resistance, our data suggest that the elevation of the free iron content by the Fur loss is likely to be the predominant factor for the Fur physiology. Overall, these results provide circumstantial evidence that Fur inactivation disturbs bacterial iron homeostasis by altering transcription of its regulon members, through which many physiological processes, such as respiration and oxidative stress response, are transformed.

Caulobacter lipid A is conditionally dispensable in the absence of fur and in the presence of anionic sphingolipids

“…Because they are impaired in iron sensing, fur mutants of other bacteria accumulate more available iron than the corresponding wild-type strains ( Liu et al, 2020 ; Wofford et al, 2019 ). We measured available iron levels using a streptonigrin (SNG) sensitivity assay ( Justino et al, 2007 ; Nachin et al, 2001 ) because SNG killing is linked to intracellular formation of oxygen radicals in the presence of iron ( Hassett et al, 1987 ; Yeowell and White, 1982 ).…”

Recent Advances in the Siderophore Biology of Shewanella

“…Siderophores synthesized by PubABC have also been shown to be important for manganese-oxide reduction (Kouzuma et al, 2012). The mechanism underpinning this phenomenon is proposed to be substantial reduction in the contents of total iron and cytochromes c. However, this is at odds with the findings of more recent studies that the absence of PubABC only marginally impacts the cellular concentrations of the both (Dong et al, 2017;Liu et al, 2018Liu et al, , 2020.…”

“…Shewanella oneidensis possesses both Fur and RyhB ( Wan et al, 2004 ; Yang et al, 2010 ). The Fur loss lowers concentrations of the total iron but increases free iron, a phenomenon attributed to constitutive and repressive expression of iron transport and iron usage proteins respectively ( Fu et al, 2018 ; Liu et al, 2020 ). The Fur box of S. oneidensis is similar to that of E. coli and the members of the predicted Fur regulons include operons for TBDRs irgA and SO_1482, siderophore biosynthesis enzyme pub , and ferrous transporter feo ( Yang et al, 2009 ; Fu et al, 2018 ).…”

“…In addition, some Shewanella species are well-known spoilers of food products and notorious fish pathogens ( Janda and Abbott, 2014 ; Lemaire et al, 2020 ). The respiratory versatility is largely attributable to a large repertoire of iron-containing proteins, iron-sulfur proteins and hemoproteins in particular, a feature requiring relatively high iron contents compared to model bacterial paradigm E. coli ( Daly et al, 2004 ; Fu et al, 2018 ; Liu et al, 2020 ). Because of this, Shewanella spp., as in the extensively studied representative Shewanella oneidensis , have evolved novel physiological characteristics to maintain iron homeostasis.…”

Caulobacter requires anionic sphingolipids and deactivation of fur to lose lipid A

“…Because they are impaired in iron sensing, fur mutants of other bacteria accumulate more available iron than the corresponding wild-type strains (Liu et al, 2020;Wofford et al, 2019).…”