Year of Award

2010

Document Type

Dissertation - Campus Access Only

Degree Type

Doctor of Philosophy (PhD)

Other Degree Name/Area of Focus

Integrative Microbiology and Biochemistry

Department or School/College

Division of Biological Sciences

Committee Chair

Stephen Sprang

Commitee Members

Scott Miller, William Holben, Brent Ryckman, Jesse Johnson

Publisher

University of Montana

Abstract

The herein described research project elucidates fundamental virus-host interactions in an emerging archaeal virus-host model, the Sulfolobus Spindle-shaped Virus (SSV) system. Virus ecology and virus-host coevolution in hyperthermophilic archaeal systems is an emerging sub-field of microbial ecology. Motivated by aspirations of using thermophilic biomolecular systems for biotechnology and by the suggestion that hyperthermophile microbiology can offer insights into the limits at which life can exist and evolve, “extremophile” microbiologists and biochemists have made significant progress in identifying and characterizing numerous hyperthermophiles that survive and thrive at temperatures above 80ºC (176ºF) as well as halophiles, barophiles, psychrophiles, and other microbes that inhabit some of the Earth’s most extreme environments.

One of the best-studied hyperthermophilic archaeal systems is that of the genus Sulfolobus. The study of Sulfolobus and similar crenarchaea rapidly accelerated after a series of seminal publications by Thomas D. Brock and colleagues in the early 1970s. The viruses and plasmids that are harbored by Sulfolobus became an intense area of research interest due in large part to extensive work by Wolfram Zillig and colleagues during the 1980s and 1990s. Both of these scientists have left a legacy largely composed of budding as well as established scientists who are enthusiastically and agressively engaged in characterizing these systems and determining what these hyperthermoacidophiles might offer the scientific community in terms biotechnology and contributions to the dialogue on “early Earth” microbial evolution. Through previous work in extremophile microbiology, biochemistry, molecular biology, and phylogenetics much has been learned. Yet, even after 40+ years of study, much remains unexplained. This is particularly true with regard to hyperthermophile virus-host interactions and the implications of the nature of such interactions on microbial evolution.

This project presents previously undescribed features of SSV-Sulfolobus interactions. Starting with a survey of allopatric SSV infectivity in pairings of viruses and hosts from geographically-distinct geothermal regions, a series of novel SSV-host infection properties are uncovered. Using techniques in microbiology, molecular biology, microscopy, biochemistry, and biophysics, a set of experiments are completed to further explore the nature of these novel observations. In addition to demonstrating that certain SSVs are capable of establishing infection beyond the genus Sulfolobus, it is also shown that a Russian SSV preferentially replicates via a lytic cycle on several Sulfolobus hosts. Both of these observations are in direct contradiction to all previous reports that characterize SSVs as “non-lytic viruses which exclusively infect the genus Sulfolobus.” Interestingly, the lytic replicator, SSVK1, appears to replicate non-lytically on a sympatric Sulfolobus host strain. Cumulatively, conclusions from this project offer novel insights regarding the nature of SSV-Sulfolobus interactions and provide a basis upon which future work can be pursued focused on elucidating the genetic and biomolecular substrates that influence the evolution of SSV virulence and that drive SSV-Sulfolobus coevolutionary processes. Finally, results from this project contribute to the development of the SSV system as a robust non-lytic reduced model system that can be used to test hypotheses regarding the emergence and evolution of non-lytic viral pathogens.

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© Copyright 2010 Ruben Michael Ceballos