Date of Award

12-14-2015

Document Type

Open Access Dissertation

Department

Marine Science

First Advisor

Seth John

Second Advisor

Tammi Richardson

Abstract

Viruses are the most numerous biological entities in the ocean, playing a key role in microbial ecology and biogeochemical cycling. In order to replicate, viruses must first infect a host and then use the host’s cellular machinery to produce new viral particles. Some of the most abundant viral hosts in the subtropical open ocean are picophytoplankton. However, picophytoplankton growth is typically constrained by nutrient availability. In many regions of the ocean, iron (Fe) is only available in very low concentrations causing growth-limitation of picophytoplankton. Interestingly, the interactions between Fe-limitation and viral infection of picophytoplankton have not been extensively studied. This dissertation adds to the field by producing novel interdisciplinary research between chemical oceanography and viral ecology. The first project in this dissertation describes a new method to count DNA-stained viruses, which is drastically less expensive than commonly used methods. The new method uses epifluorescence microscopy to enumerate fluorescently stained viruses. The virus sample is combined with a known concentration of silica beads and wet mounted directly onto a slide. Viral concentration is then determined by the relative abundance of viruses and silica beads in the sample. The second project describes one-step growth curves of viruses Syn9, S-SM1, and S-PM2 infecting host Synechococcus WH7803 grown under both nutrient-replete and Fe-limited conditions. The results indicate that for these virus strains, decreased host growth rate from Fe-limitation seems to have no effect on viral reproduction. The third project presents data on the internal cellular concentrations of nutrients and trace elements when picophytoplankton are grown under varying conditions. Determining internal cellular concentrations are important when attempting to understand what nutrients are absorbed and then released by the host during viral infection and lysis. We find that Fe-limitation of cyanobacteria cells elicits a similar response to that of P-limitation, causing an overall decrease in cellular P concentration under both conditions. Overall, this dissertation provides a more complete understanding of differences in viral and cellular production of Fe-limited hosts and suggests a possible role for Fe in the efficiency of the marine microbial loop, carbon, and nitrogen cycle.

Rights

© 2015, Brady Robert Cunningham

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