The Role of Siderophores in Fe Acquisition by Aerobic Bacteria: Fe Oxide Nanoparticles and Natural Organic Matter

Thursday, March 24, 2011

Presenter

Patricia Maurice

Dr. Patricia Maurice, Ph.D., is a Professor of Civil Engineering and Geological Sciences as well as the Director of the Center for Environmental Science and Technology at the University of Notre Dame.

Abstract: Fe is an essential nutrient for nearly all organisms. Yet, dissolved concentrations of Fe in aerobic, circum-neutral environments are typically ~10 orders of magnitude less than biological requirements.  In order to acquire Fe, aerobic bacteria often exude low molecular weight organic ligands known as siderophores, which have extremely high Fe(III) binding affinities.  Siderophores have been shown to play important roles in Fe mobilization from Fe-bearing minerals.
This research investigated Fe acquisition from hematite (a-Fe2O3), nanohematite, and natural organic matter (NOM) by a siderophore-producing Pseudomonas mendocina bacterium and an engineered siderophore (-) mutant that was incapable of producing and releasing siderophore(s). Microbial growth (population size) under Fe-limited batch conditions was monitored via optical density. In addition, a biosensor assay used siderophore transcriptional output as a measure of cellular Fe status as an independent means of determining how readily Fe was obtained from the various potential sources.

Results of bioassay analysis showed that (1) siderophores work in conjunction with other organic ligands commonly found in soils; (2) in the absence of other organic ligands, siderophores are required for Fe acquisition from hematite particles > 10 nm in size but not for particles < 10 nm; and (3) NOM-bound Fe is highly bioavailable and siderophores are not needed for Fe acquisition from NOM.  Preliminary results suggest that a cell-wall-associated reductive mechanism allows for Fe acquisition from nano-scale Fe sources but not from larger particles.  Overall, this research demonstrates that nanomaterials may interact with bacteria through unique pathways.