Author

Andrew W. Han

Date

November 2011

Document Type

Dissertation

Degree Name

Ph.D.

Institution

Oregon Health & Science University

Abstract

Shipworms are marine bivalve mollusks (Family Teredinidae) that burrow into wood for shelter and a source of food. They harbor a closely related, yet phylogenetically distinct, group of bacterial endosymbionts in bacteriocytes located in the gills. This endosymbiotic community is believed to support the host’s nutrition in multiple ways. The symbionts have been shown to produce cellulolytic enzymes that are believed to aid the host in the digestion of wood. They also provide a source of fixed nitrogen through the process of nitrogen fixation to supplement the nitrogen-poor diet of wood. In host systems, iron is tightly regulated and bound by host proteins, limiting its availability to associated microbes. Due to their implicated role in nitrogen fixation, shipworm symbionts may have an even higher demand for iron in the host beyond those required for normal growth. One of the strategies utilized by microbes in the acquisition of iron is through the production of low molecular weight compounds with high affinity for Fe(III) called siderophores. This work presents the structures, biosynthesis, and possible roles for siderophores in the shipworm system. One of the most well studied shipworm symbiont is Teredinibacter turnerae. Chapter 2 presents the characterization of a novel catecholate siderophore produced by T. turnerae T7901, called turnerbactin. In addition, the biosynthetic pathway for turnerbactin is analyzed. Chapter 3 introduces other members of the shipworm endosymbiotic community and addresses the potential for siderophore production in these members through a mass spectrometry-based survey and through bioinformatic analysis of genomic data. This overview of the siderophore potential of symbionts suggests the predomination of catecholate-type siderophores from this community of bacteria. Chapter 4 analyzes how siderophores might be utilized by shipworm symbionts and presents the potential for siderophores to mediate interactions between symbionts. The combined use of cross-streaking experiments and disc-diffusion assays indicate that siderophores have the potential to inhibit the growth of fellow symbionts. This suggests that the endosymbiotic community of shipworms does not work as a cooperative unit in the acquisition of iron.

Identifier

doi:10.6083/M4G73BQ8

Division

Div. of Environmental & Biomolecular Systems

School

School of Medicine

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