Date of Award

1-12-2006

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biology

First Advisor

Dr. Zehava Eichenbaum - Chair

Second Advisor

Dr. Sidney Crow

Third Advisor

Dr. Phang C. Tai

Abstract

A limited understanding of iron uptake mechanisms is available for Streptococcus pyogenes, a hemolytic human pathogen capable of using a variety of hemoproteins in addition to ferric and ferrous iron. This study characterizes the transporters of iron-complexes siuADBG (for streptococcal iron uptake) and siaABC (for streptococcal iron acquisition). These ABC-type transporters are encoded by iron regulated operons and their protein products are homologous to components of heme and siderophore transporters found in both Gram-positive and Gram-negative bacteria. Mutants of the membrane permeases siuG and siaB were constructed and characterized. Mutations in both transporters demonstrated growth reduction in comparison to the parent strain when grown in complex medium containing iron in the form of hemoglobin. The addition of heme to the growth medium inhibited ferric uptake by the wild-type while the addition of protoporphyrin IX did not, suggesting that heme utilization as an iron source is responsible for the inhibition of ferric accumulation. Inactivation of siuG reduced the ability of heme to inhibit ferric incorporation by the cells. Inactivation of siaB in addition to siuG had a cumulative effect, indicating that both siu and sia transporters are involved in heme utilization. We also demonstrated that purified rSiaA, the surface receptor of SiaABC, binds heme and hemoglobin in vitro, and we propose a mechanism of heme binding by SiaA. Studies in a zebrafish infection model revealed that the siuG mutant was attenuated in producing disease. While the siaB mutant also presented virulence attenuation, infection by this mutant was characterized by an increase in the host inflammatory response. These observations show that iron acquisition is important for S. pyogenes virulence. We propose that the SiaABC and SiuADBG, together with the multi-metal transporter MtsABC, are involved in iron acquisition from different iron sources present in the human body, thus contributing to the survival and pathogenesis of S. pyogenes.

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Biology Commons

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