Graduate Program

Biological Sciences

Degree Name

Master of Science (MS)

Semester of Degree Completion

Summer 2026

Thesis Director

Gopal R. Periyannan

Thesis Committee Member

Britto P. Nathan

Thesis Committee Member

Thomas Canam

Thesis Committee Member

Gary A. Bulla

Creative Commons License

Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License.

Abstract

The persistence of microbial communities in fluctuating environments is largely governed by biofilm-mediated resilience, a critical feature of both clinical and environmental microbiomes. While antibiotic resistance is often the focus, the fundamental molecular mechanisms driving the bacterial community's stability under chemical stress remain underexplored. This study utilizes Caulobacter vibrioides CB15N (Syn: Caulobacter crescentus CB15N), a metabolically versatile alphaproteobacterium, to investigate how individual taxa navigate the transition from planktonic to biofilm or bioaggregate states when challenged by toxic aromatic hydrocarbons.

We evaluated the niche-specific fitness and bioaggregate-forming capacity of C. vibrioides CB15N using benzaldehyde, protocatechuate, and phthalate as primary carbon sources. Quantitative growth kinetics and microscopic structural analyses revealed that substrate-specific metabolic pathways directly dictate biofilm architecture. High-performance liquid chromatography (HPLC) confirmed distinct substrate utilization dynamics, suggesting that the chemical landscape of the microenvironment serves as a primary driver of microbial developmental shifts.

Biochemical profile of the extracellular polymeric substance (EPS) matrix—analyzed via FTIR spectroscopy and quantification of uronic acids, proteins, and carbohydrates—demonstrated that carbon source availability fundamentally reshapes the "molecular glue" holding the community together.

Furthermore, we identified critical cellular envelope adaptations, including shifts in lipopolysaccharides (LPS) and outer membrane proteins. RT-PCR analysis of extracytoplasmic function (ECF) sigma factors further elucidated the regulatory circuitry that allows this microbe to sense and respond to environmental stressors.

Collectively, these findings highlight the metabolic flexibility and physiological adaptations required for survival within complex microbial landscapes. By characterizing these stress-responsive mechanisms, this study establishes C. vibrioides CB15N as a robust model for understanding the broader principles of biofilm/bioaggregate-driven resilience and community persistence in nutrient-limited and toxic environments.

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Available for download on Thursday, August 19, 2027

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