Temperature Control of a 3,4-Dihydroxybenzoate (Protocatechuate)-Based Siderophore in Bacillus anthracis

Abstract

Bacillus anthracis Sterne produced a catecholate siderophore named anthrachelin that was based on 3,4-dihydroxybenzoic acid (3,4-DHB, or protocatechuic acid), a catechol moiety previously unreported as a siderophore component. During iron restriction, both anthrachelin and free 3,4-DHB were excreted. Growth at 37 degrees C (as compared with 23 degrees C) decreased excretion of anthrachelin but not its precursor 3,4-DHB, suggesting that anthrachelin assembly is temperature regulated. A plasmidless strain also produced anthrachelin in an iron- and temperature-regulated fashion, indicating that anthrachelin genes are chromosomal. In addition to anthrachelin-mediated iron delivery, B. anthracis also used heme, hemoproteins, iron-transferrin, and certain heterologous siderophores (xenosiderophores) produced by other microorganisms as iron sources. Downregulation of anthrachelin production at the temperature of the mammalian host (which triggers toxin production in this pathogen) may focus the B. anthracis iron acquisition systems to exploit the iron sources prevailing in the infected host.

Production of Catechol-Siderophore and Utilization of Transferrin-Bound Iron in Bacillus cereus

“…4,5) Bacillus species other than B. cereus are also known to produce catechol-siderophores. 6,7) However, transferrin receptor-mediated IUS plays an important role in the uptake of iron from transferrin in certain bacteria, such as Haemophilus and Neisseria species, which are unable to produce siderophores. 4,5) In Gram-positive bacteria, only Staphylococcus aureus and S. epidermidis have been known to express a putative transferrin receptor on their cell walls, but the role of this receptor with regard to the uptake of iron from transferrin remains controversial.…”

“…Therefore, it was necessary to demonstrate B. cereus' siderophore production by more sensitive or specific assay methods. Because other bacillus species have been reported to produce catechol-siderophore(s), 6,7) we attempted to demonstrate the production of catechol-siderophore(s) using the Arnow test, 11) a specific chemical assay for catecholsiderophore(s). B. cereus was able to produce catecholsiderophore(s), as seen in Fig.…”

“…This versatility of B. cereus was similar to that observed in B. anthracis. 7) Considering that the siderophore-mediated IUS of B. anthracis played an important role in its in vivo growth and virulence characteristics, 18) this might also be true of the siderophore-mediated IUS of B. cereus.…”

“…4,5) Bacillus species other than B. cereus are also known to be able to produce catechol-siderophores, and thus clearly possess siderophore-mediated IUS. 6,7) In this study, we attempted to ascertain whether B. cereus is able to produce catechol-siderophores and utilize transferrin-bound iron, the main iron source encountered by this organism during human infections. We found that B. cereus exhibited the clear ability to produce catechol-siderophores and to utilize transferrin-bound iron as an iron source for growth.…”

Characterization of a Bacillus subtilis transporter for petrobactin, an anthrax stealth siderophore

“…K d of 4.2 Ϯ 0.1 nM for Fe (3, indicates that the receptor may be at least 30-fold more specific for ferric 3,4-DHB than for FePB (Table 1). Although 3,4-DHB is secreted in large quantities by B. anthracis, its role as a siderophore is unclear (27). Similar to the BB precursor itoic acid (2,3-dihydroxybenzoyl glycine) produced by B. subtilis, such bidentate ligands have much lower affinity for iron than the hexadentate siderophores.…”