Investigating a Link Between Cold Stress and Bacterial Leak from the Gut of Locusta Migratoria

Abstract

Following prolonged low temperature exposure, chill-susceptible insects can incur chilling injuries that manifest as motor deficits and tissue damage. This tissue damage is thought to be driven by a loss of ion and water homeostasis, characterized by elevated potassium concentration in the hemolymph (hyperkalemia). The insect gut plays a major role in the maintenance of ion and water balance, and gut epithelial barrier function is compromised during chilling, which can contribute to the leak of water and solutes across the gut wall. The insect gut also houses an abundant bacterial population which can contribute to the host's cold tolerance. In recent years, however, a growing number of studies have reported increased activation of the insect immune system following a cold stress, suggesting that cold stress may cause bacterial infection. For my research, I hypothesized that prolonged cold stresses result in the leak of bacteria from the gut into the surrounding hemolymph as a possible explanation for the immune activation. With locusts as my model insect, I used an E. coli strain that expresses a fluorescent marker (GFPmut3) to track bacterial leak from the gut. After a period of feeding on wheat that was soaked in a concentrated solution of the bacteria, locusts were exposed to -2°C for varying lengths of time before hemolymph was extracted and plated on agar media to facilitate bacterial colony growth. Surprisingly, I found no evidence of bacterial leak as no colonies were observed regardless of cold exposure length. My research strongly suggests that gut barrier integrity is well maintained even after severe cold stresses and is sufficient enough to prevent the leak of whole bacteria across the gut wall, which opens up other possible explanations as to why immune activation occurs following cold exposures in insects.iii AcknowledgementsMy graduate school experience here at Carleton was a very fulfilling and enriching one.The people I've met, the opportunities I've been given, and the lessons I've learned may be innumerable, but they all mean a great deal to me.Thank you, Heath, for all your support and mentorship over the past four years, especially through a pandemic! A large part of my growth as a scientist has been, in large part, because of you going above and beyond for us. From publishing a paper to attending conferences, I can definitely say that I've become a lot better at communicating research to others and, more importantly, become even better at thinking independently as a researcher. I can certainly look back now and see how far I've come, so thank you once more. I'd also like to extend this thanks to Jeff Dawson. Thank you for your monumental help and support at the beginning of my MSc.