Graduate Defense: Jessica Bernardin

Dissertation Information

Title: The Functional Dynamics Of Bacterial Communities In Relation To Environmental Selection And Host Health In A Pitcher Plant Model System

Program: Doctor of Philosophy in Ecology, Evolution, and Behavior

Advisor: Dr. Leonora Bittleston, Biological Sciences

Committee Members: Dr. Marie-Anne de Graaff, Biological Sciences; Dr. Kevin Feris, Biological Sciences; and Dr. Sarah Gray, Biological Sciences

Abstract

Our research investigates the function and composition of microbial communities across various conditions, shedding light on microbial community dynamics and plant-microbe interactions. Despite the crucial role microbes play in Earth’s ecosystems, many questions remain about how microbiomes function and their direct impact on host health.

The first chapter explores the links between bacterial community function and the growth of purple pitcher plants (Sarracenia purpurea). We introduced three distinct bacterial communities into sterile pitchers to assess their effects on plant health. Different bacterial functions influenced plant traits, with communities rich in decomposition and secondary metabolite production traits leading to significantly larger leaves compared to bacteria-free pitchers. Additionally, the bacterial community associated with larger pitchers exhibited increased expression of transcripts linked to microbially-produced plant hormones.

The second chapter examines how environmental factors shape microbial community function and composition. By subjecting a diverse microbial community to various abiotic conditions—varying pH, nutrient levels, and temperatures—we observed clear shifts in both bacterial community composition and function over time. Different abiotic conditions impacted microbial functions differently; for instance, temperature stress boosted chitinase activity while suppressing protease activity. We also noted shifts in microbial community composition based on interactions between temperature, pH, and nutrients.

In chapter three, we investigate how variations in arthropod detritus affect microbial-driven decomposition and community function. Using sterile mesh bags filled with different types of sterile arthropod prey, we assessed whether prey type influenced decomposition rates in pitcher plants. We found that prey with higher exoskeleton content, like ants and beetles, decomposed at a slower rate compared to prey with lower exoskeleton content, such as flies. Additionally, protease activity was highest in the fly treatment, indicating varied effects of different prey types on microbial function and composition.

In conclusion, this research presents a culmination of experiments, observations, and analyses linking microbial communities to their environment and hosts. We underscore the interconnectedness of communities and provide evidence for the importance of understanding both community composition and function.