The Functional Dynamics of Bacterial Communities in Relation to Environmental
Selection and Host Health in a Pitcher Plant Model System
Authors: Bernardin Jessica Rae 
Published: January 2025

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.

Overall, we found that two major themes developed throughout this research. The
first is, microbial community composition does not always predict community
function. For example, in Chapter 1, the relative abundance of the top 20 taxa
was very similar across functionally dissimilar communities. Additionally, in
Chapter 2, we found that abiotic conditions influenced community function and
composition differently. Lastly, in Chapter 3 we found that large shifts in the
rates of insect decomposition resulted from relatively small changes in
community structure, making it difficult to use composition to predict function.
The second theme of this research can be summarized by saying, that microbial
function matters. We found evidence overall that small differences in microbial
community function were often driven by even smaller differences in composition,
despite this, we found outsized effects of function on plant growth and prey
decomposition. This further illustrates that community dynamics are complex,
multiple measures of community composition and function should be integrated to
better understand them. In conclusion, this research presents a culmination of
experiments, observations, and analyses linking microbial communities to their
environment and hosts. We find that the minute interactions between microbes in
these communities can have widespread implications for ecosystem health.
Microbial function is a critical, yet often overlooked, aspect of ecosystem
dynamics. By recognizing the diverse influences of microbial function, we gain
insights for more innovative approaches in research and conservation.