Graduation Year

2019

Document Type

Thesis

Degree

M.S.

Degree Name

Master of Science (M.S.)

Degree Granting Department

Marine Science

Major Professor

Mya Breitbart, Ph.D.

Co-Major Professor

Kristen Buck, Ph.D.

Committee Member

Karyna Rosario, Ph.D.

Keywords

bacteria, bacteriophage, colloidal, ligand, marine, phage

Abstract

Iron is an essential micronutrient for phytoplankton metabolism that limits growth in many regions of the surface ocean. More than 99.9% of oceanic dissolved iron is organically complexed to an iron-binding ligand, many of which have yet to be characterized. This thesis puts forth the Ferrojan Horse Hypothesis, which predicts a role for marine phages in oceanic iron cycling. Based on evidence from non-marine model systems, the Ferrojan Horse Hypothesis suggests that some marine phages (short for bacteriophages, or viruses that infect bacteria) can use iron as a “Trojan Horse” to gain access to host siderophore-bound iron receptors for infection. After taking over the host bacterial cell, new phages are produced which potentially contain iron from host storages, thus decreasing the amount of dissolved iron available for remineralization upon lysis. Escherichia coli and its associated phages were used as a model system for method development to facilitate testing of aspects of the Ferrojan Horse Hypothesis. The stable isotope 57Fe was used as a tracer to determine the quantity and source of iron to progeny phages. E. coli cells were grown in minimal media with 57Fe as the sole iron source, infected with phage T4 or T5, and progeny phages were purified. After lysis, the 57Fe content was quantified by inductively coupled plasma mass spectrometry (ICP-MS), and phage concentrations were quantified by nucleic acid staining and epifluorescence microscopy. The 57Fe was significantly higher in purified T4 and T5 phage samples than in bacterial lysis controls, and samples contained 166-2,269 57Fe atoms per phage. Greater than 90% of the total 57Fe in each experiment pre-lysis was located within bacterial cells, as opposed to the external media, indicating the source of 57Fe to progeny phages was likely from host storages. The methods developed in this study lay the groundwork for testing facets of the Ferrojan Horse Hypothesis in a marine phage-host system. If the principles demonstrated in this model phage-host system apply to marine phages as well, this research indicates a potentially significant role for viruses in oceanic iron cycling.

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