Extracellular iron reductase activity produced by Listeria monocytogenes
- PDF / 70,071 Bytes
- 7 Pages / 595 x 842 pts (A4) Page_size
- 104 Downloads / 216 Views
© Springer-Verlag 1996
O R I G I N A L PA P E R
Esau Barchini · Richard E. Cowart
Extracellular iron reductase activity produced by Listeria monocytogenes
Received: 12 March 1996 / Accepted: 16 April 1996
Abstract Little is known about how pathogenic microorganisms that do not produce low-molecular-weight ironchelating agents, termed siderophores, acquire iron from their environment. We have identified an extracellular enzyme produced by Listeria monocytogenes that can mobilize iron from a variety of iron-chelate complexes via reduction of the metal. The iron reductase requires Mg2+, flavin mononucleotide (FMN), and reduced nicotinamide adenine dinucleotide (NADH) for activity. Saturation kinetics were found when initial velocity studies of iron reduction were carried out as a function of variable FMN concentrations in the presence of 100 µM NADH and 10 mM Mg2+. Hyperbolic kinetics were also found when these studies were repeated as a function of variable NADH concentrations along with 20 µM FMN and 10 mM Mg2+. This process of extracellular reduction, in all likelihood, could be involved in the mobilization of iron from soils and aqueous environments and from host tissues in pathogenic processes. This is the first report of the extracellular enzymic reduction of iron by microorganisms. Key words Iron · Listeria monocytogenes · Extracellular iron reduction · NADH:iron reductase Abbreviations BPS Bathophenanthrolinedisulfonic acid · Fe3+-NTA Ferric nitrilotriacetic acid
This work was carried out in part by E. Barchini in fulfillment of the research requirements for the degree Bachelor of Science E. Barchini · R. E. Cowart Department of Microbiology/Immunology, Oral Roberts University School of Medicine, Tulsa, OK 74137, USA R. E. Cowart (Y) Department of Medical Specialties, Section of Infectious Diseases, Box 47, University of Texas M. D. Anderson Cancer Center, 1515 Holcombe Blvd., Houston, TX 77030, USA Tel. +1-713-745-1371; Fax +1-713-794-4488 e-mail: [email protected]
Introduction Microorganisms face considerable thermodynamic and kinetic barriers in mobilizing iron from their surrounding environments. At neutral pH, the concentration of free iron is between 10–17 and 10–18 M, while at pH 3, it is about 1 µM; the latter is generally thought to be the minimum iron concentration required to support a growing population of microorganisms (Neilands et al. 1987). Microorganisms are known to transport iron using inducible, virtually ferric-specific chelators termed siderophores. Some microorganisms, however, do not utilize siderophores in the transport of iron, which creates an apparent dilemma. It has been reported that Listeria monocytogenes, which has not been found to synthesize siderophores, produces an extracellular iron-reducing agent that rapidly mobilizes iron from transferrin as a likely means of acquiring iron (Cowart and Foster 1985). L. monocytogenes has been later shown to acquire Fe2+ and Fe3+-citrate using a citrate-inducible system at its cell surface (Adams et al. 1990). Recent
Data Loading...
