Reduction of exogenous ferric iron by a surface-associated ferric reductase of Listeria spp.

Abstract

The reduction of exogenous ferric iron by Listeria monocytogenes, a Grampositive food-borne pathogen, was investigated. Using an assay incorporating the ferrous iron chelator ferrozine, we showed that intact cells of L. monocytogenes, when exposed to ferric iron, were able to rapidly reduce and solubilize the iron to the ferrous form. Reduction occurred only after direct contact between the bacteria and the iron source. A number of different ferric iron chelates, including transferrin and lactoferrin-bound iron, haemoglobin, ferritin, and iron complexed to siderophores, could be reduced. The ferric reductase activity was expressed by both reference strains and clinical isolates of L. monocytogenes and by all other species of Lisferia, although significant quantitative differences were observed. In L. monocytogenes, the expression of ferric reductase was not affected by the growth phase of the bacteria nor by the presence or absence of iron in the growth medium. However, expression was greatly reduced in bacteria grown anaerobically and when cultured in media of reduced pH. In addition, bacteria grown at a cold temperature displayed greater ferric reductase activity than cells grown at higher temperatures. A surface-associated ferric reductase system may be one component of a general iron scavenging mechanism which can be used by Listeria growing in a variety of environments.

Iron acquisition and virulence in Helicobacter pylori: a major role for FeoB, a high‐affinity ferrous iron transporter

“…Secreted Fe 31 reductants have been described for several bacteria (Adams et al, 1990;Homuth et al, 1998) and for yeasts (Dancis et al, 1990;Nyhus et al, 1997). Precedence for membrane-associated Fe 31 reductase activities also exists (Dailey and Lascelles, 1977;Fischer et al, 1990;Deneer et al, 1995;Mazoy and Lemos, 1996). It was postulated in the study of Worst et al (1998) (Fig.…”

Antibacterial Activity of Recombinant Human Lactoferrin from Rice: Effect of Heat Treatment

“…14) It has been shown that some bacteria, like L. monocytogenes which does not produce any siderophore, can use the exogenous siderophores and catechol ligands produced by other bacteria 15) or can express a surface-associated ferric reductase. 16) Another mechanism for the antibacterial activity of lactoferrin, which is independent of its iron saturation, is the direct binding of lactoferrin to the bacteria. With Gram-negative bacteria, lactoferrin induces the rapid release of lipopolysaccharide (LPS), damaging the outer membrane and increasing its permeability.…”

Role of the twin-arginine translocase (tat) system in iron uptake in Listeria monocytogenes

“…Although Listeria does not produce siderophores, it is able to obtain iron using either exogenous siderophores produced by other micro-organisms or natural catechol compounds widespread in the environment (Jin et al, 2006;Xiao et al, 2011). Physiological data suggest the existence of strong surface-associated ferric reductase activity in L. monocytogenes (Deneer et al, 1995;Cowart, 2002), but no genetic determinant for the enzyme has been identified in its genome. The reduction of iron from ferric to ferrous is critical because ferric iron is insoluble and is not possible to mobilize in its unbound state.…”

“…Ferric reductase activity in the tatC and fepB mutants L. monocytogenes has been shown to have a strong surfaceassociated ferric reductase enzyme (Deneer et al, 1995;Cowart, 2002). However, genome searches for homologous sequences encoding ferric reductase enzymes in other Gram-positive bacteria did not show any significant homology.…”

“…Standard whole-cell ferric reductase assays were carried out by trapping Fe 2+ as a coloured complex with ferrozine, as described previously with some modifications (Deneer et al, 1995). Briefly, cells were grown in LB containing 0.1 % (w/v) glucose at 37 uC with 200 r.p.m.…”