The Proteomic Response of the Probiotic Pediococcus acidilactici R1001 after Exposure to the Cell-free Supernatant of the Pathogen Listeria monocytogenes ATCC 7644

THE PROTEOMIC RESPONSE OF THE PROBIOTIC PEDIOCOCCUS ACIDILACTICI R1001 AFTER EXPOSURE TO THE CELL-FREE SUPERNATANT OF THE PATHOGEN LISTERIA MONOCYTOGENES ATCC 7644 Sherise Charles Advisors: University of Guelph, 2016 Dr. Cezar M. Khursigara Dr. Reggie Lo Probiotics are live microorganisms that exert a benefit to the host when ingested, and are commercially available for use in many fields. They are capable of excluding pathogenic bacteria from the gastrointestinal tract of the host through various mechanisms including, but not limited to, inhibition of growth and survival of the pathogen, interference with pathogen adhesion to the host epithelium, as well as production of bacteriocins and short chain fatty acids. However, research on the influence of pathogenic bacteria on probiotics – whether through their physical interactions or through induced changes in the environment – is limited. This thesis investigates changes in the proteome of a commercially used probiotic in response to exposure to pathogen supernatants. Culturing the probiotic Pediococcus acidilactici in cell culture medium and Listeria monocytogenes supernatant, we found that P. acidilactici showed changes in protein abundance corresponding to an adaptation to the growth environment, though not necessarily in response to the pathogen supernatant. This work provides a foundation for analyzing the molecular changes in probiotics that allows them to adapt to their environment and interact effectively with pathogens. iii Acknowledgements First and foremost, I would like to thank my advisor Dr. Cezar Khursigara for granting me the wonderful and unforgettable opportunity to be a graduate student in his lab. His patience, guidance, kindness and encouragement have helped me to work through any difficulties I encountered with confidence, as I knew I had his support. He was always open to discussion and very passionate about his craft, and I owe a lot to him for my development as a scientist over these few years. I would also like to thank my advisory committee – Dr. Reggie Lo, who always offered sound advice, and Dr. Marc Habash, for his guidance and support to keep me on track. Furthermore, I would like to thank Jonathan Krieger and Paul Taylor at the SPARC BioCentre at the Hospital for Sick Children for all their correspondence and help with our mass spectrometry work. To my labmates, past and present, words cannot express how lucky I feel to have met you all. Special thanks Emily Vis, who was the starting point for me in the lab and who made sure I had all the tools I would need to get through my own project, Alison Berezuk for always having an answer to any problem, Amber Park for her help and infinite wisdom on all things proteomic, Erin Anderson for always lending an ear, and Matt Surette and Mara Goodyear for the funny stories and much needed science pep talks. Kaitlyn Oliphant and Rafael Peixoto, I am glad that we all got stuck in our small office together. Thanks for always being there on the good days as well as the off days. I need to say thank you to all the great people I have met during my time here. You all made each day incredible. Last but most definitely not least, I would like to thank my amazing parents. Their love and support has stretched far beyond my graduate studies and I am eternally grateful for all they have done to get me here.