Alexander L. Kula Thesis Defense: Project Description
Title: Experimental Evolution of Specialism in a Wild Virus
A pathogen’s ability to successfully replicate and persist within a new host population is fraught with obstacles. While an expanded host-range allows for a greater chance at successful replication, such generalists are typically outcompeted by species which have specialized and adapted host-specific features. Although the most ubiquitous species on earth, very few bacteria-infecting viral species (bacteriophages) with truly broad host-ranges have been identified; this is partially due to the fact that only a small fraction of bacteria (and thus likely hosts) are amenable to laboratory conditions. Nevertheless, the processes of expanding as well as narrowing host-range are not well understood despite their profound importance for furthering our understanding of viral pathogens, be it bacteriophages or viral species impacting human health.
Following the successful isolation of novel bacteriophage named ФHabibi, we identified this generalist species’ broad host-range, including several Enterobacteriaceae. In order to examine the cost of generalism, we propagated 30 lines of ФHabibi: 10 lines were exposed only to naïve E. coli C cells, 10 lines were exposed only to naïve P. aeruginosa, and 10 alternated every 16 generations between naïve populations of the two (serving as a control). While no reduction in fitness was observed on either host population for the control lines, this was not the case for either of the experimental conditions. Lines propagated through E. coli C cultures were more fit in E. coli C. Likewise, lines propagated through P. aeruginosa cultures were more fit in P. aeruginosa. Moreover, specialization as well as changes in phage development, from lytic to lysogenic and pseudolysogenic, were observed as a result of restricting host diversity thus providing insight into the cost and consequences of host-range.
I would like to thank my committee members Dr. Catherine Putonti, Dr. Domenic Castignetti, and Dr. Sushma Reddy for their assistance and comments on the thesis. Thank you to Dr. Siobhan Watkins for her assistance throughout the research project, as well as her assistance in writing the thesis. Thank you to Katherine Bruder and Kema Malki for their work in obtaining the TEM images of ФHabibi. Thank you to the members of the Putonti Lab at Loyola University Chicago for their assistance in the laboratory. Thank you to Mr. Joe Schleup for assistance with the TEM, as well as stereomicroscope, and Dr. Zhenkang Xu for assistance sequencing the ancestral strain. This work is funded in part by a Research Support grant from Loyola University Chicago as well as NSF support (C.P. award #1149387.
Alexander Kula was born and raised in southeast Wisconsin. He attended Loyola University of Chicago while he was an undergraduate, obtaining a Bachelor of Science degree in both Biology and Anthropology.
Dr. Catherine Putonti
Dr. Domenic Castignetti
Dr. Sushma Reddy