Enzyme Activities in the Intestinal Layers of Teleost Fishes: Endogenous Versus Exogenous Contribution
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ENZYME ACTIVITIES IN THE INTESTINAL LAYERS OF TELEOST FISHES: ENDOGENOUS VERSUS EXOGENOUS CONTRIBUTION NAHID VAGHARFARD A THESIS SUBMITTED TO THE FACULTY OF GRADUATE STUDIES IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE GRADUATE PROGRAM IN BIOLOGY YORK UNIVERSITY TORONTO, ONTARIO DECEMBER 2020 © Nahid Vagharfard, 2020 ABSTRACT Digestive enzymes are essential for the catabolism of macromolecules and are produced endogenously by the animal or exogenously by the gastrointestinal bacteria. This thesis explored the contribution of endogenous versus exogenous trypsin, lipase, and cellulase production across dietary niches by separating the intestines of fed and unfed carnivorous rainbow trout, omnivorous goldfish, and herbivorous central stonerollers into layers where bacteria were present or absent. Trypsin and lipase were both endogenously and exogenously produced in a species-specific manner, whereas cellulase was solely produced by bacteria in all three fishes. As well, feeding generally decreased enzyme activities in most cases. Furthermore, dietary manipulation of goldfish caused the elimination of most trypsin (via endogenous responses) and cellulase (via mostly exogenous responses) activities. Collectively, these findings elucidate the proportional contribution of the microbe host and gastrointestinal bacteria to digestive enzyme production in various fishes with different diets, and provide insight into the digestive functions of environmentally and economically important vertebrates. ii ACKNOWLEDGEMENTS I would like to express my sincerest gratitude to my supervisor, Dr. Carol Bucking, for being so helpful throughout my studies. Thank you for all of your guidance and encouragement these last three years, as well as for all of the opportunities you have provided me with to excel as a researcher. You have made me develop a deep appreciation for research. I would also like to extend my thanks to Dr. Raymond Kwong, my advisor, who was available to help me whenever I needed it. Your feedback has strengthened my abilities as a researcher. Also, thanks to members of the Kwong lab. You guys have been great neighbours! To my peers – thank you for making this whole experience a memorable one. Helen Moshe, without you, I don’t know what I would have done. Our shared love for Titanic, crime podcasts, music, and much more is something I will always cherish. There’s no one else I would have rather experienced everything (e.g. conferences, late lab nights, washing aquarium tanks, and Bamfield just to name a few) with. I also thank all past and present members of the Bucking lab, including Leah Turner, Eleni Diakanastasis, and Joseph Ramos. Thanks to Chun Chih Chen for his mentorship, time, and Illustrator skills. Thank you to Aryan Lajevardi, Farwa Sajadi, Sheralyn Au (and her artistic abilities), and all of my other friends for their continuous support. My greatest thanks go to my family, who have done nothing but support me in every way possible along every step of the way. To my parents especially, thank you for believing in me and always pushing me to strive for my best. It is because of you that I have gotten this far, and I hope I have made you proud. iii TABLE OF CONTENTS ABSTRACT ................................................................................................................................... ii ACKNOWLEDGEMENTS ........................................................................................................ iii TABLE OF CONTENTS ............................................................................................................ iv LIST OF TABLES ...................................................................................................................... vii LIST OF FIGURES ................................................................................................................... viii ABBREVIATIONS ....................................................................................................................... x CHAPTER 1: GENERAL BACKGROUND.............................................................................. 1 1.1. Teleost digestive systems ..................................................................................................... 1 1.1.1. Gastrointestinal morphology .................................................................................................. 1 1.2. Digestive enzymes ............................................................................................................... 4 1.2.1. Trypsin .................................................................................................................................... 5 1.2.2. Lipase ...................................................................................................................................... 6 1.2.3. Cellulase ................................................................................................................................. 7 1.3. Gastrointestinal microbiota of teleosts................................................................................. 8 1.4. Impact of diet ....................................................................................................................... 9 1.5. Rationale ............................................................................................................................ 10 1.5.1. Species under study .............................................................................................................. 10 1.6. Objectives and hypotheses ................................................................................................. 11 CHAPTER 2: TRYPSIN, LIPASE, AND CELLULASE ACTIVITIES IN THE INTESTINAL LAYERS OF THREE TELEOST SPECIES WITH DIFFERENT DIETS 16 2.1. INTRODUCTION ............................................................................................................. 16 2.1.1. Endogenous production of digestive enzymes ..................................................................... 16 2.1.2. Exogenous production of digestive enzymes ....................................................................... 17 2.1.3. Intestinal microbiota ............................................................................................................. 19 2.1.4. Species comparisons ............................................................................................................. 20 2.1.5. Hypotheses ............................................................................................................................ 20 2.2. MATERIALS AND METHODS ....................................................................................... 22 2.2.1. Experimental animals, housing, and care ............................................................................. 22 2.2.2. Dissections ............................................................................................................................ 23 2.2.3. Genomic DNA extraction ..................................................................................................... 24 2.2.4. Polymerase chain reaction and gel electrophoresis .............................................................. 25 2.2.5. Enzyme assays ...................................................................................................................... 27 2.2.5.1. Trypsin enzyme assay ........................................................................................................ 28 2.2.5.2. Lipase enzyme assay .......................................................................................................... 29 2.2.5.3. Cellulase enzyme assay ...................................................................................................... 31 2.2.6. Bradford protein assay .......................................................................................................... 32 iv 2.2.7. Statistical analyses ................................................................................................................ 33 2.3. RESULTS .......................................................................................................................... 37 2.3.1. Bacterial detection in the intestinal layers ............................................................................ 37 2.3.2. Trypsin activity levels........................................................................................................... 37 2.3.2.1. Intestinal epithelial layers of each species ......................................................................... 37 2.3.2.2. Interspecies comparisons of intestinal epithelial layers ..................................................... 39 2.3.2.3. Interspecies comparisons of the whole intestine, chyme, and intestinal muscle ................ 40 2.3.3. Lipase activity levels ............................................................................................................ 41 2.3.3.1. Intestinal epithelial layers of each species ......................................................................... 41 2.3.3.2. Interspecies comparisons of intestinal epithelial layers ..................................................... 43 2.3.3.3. Interspecies comparisons of the whole intestine, chyme, and intestinal muscle ................ 44 2.3.4. Cellulase activity levels ........................................................................................................ 45 2.3.4.1. Intestinal epithelial