Kaya Chun

Date of Award

6-2025

Document Type

Thesis - SCU Access Only

Publisher

Santa Clara : Santa Clara University, 2025

Department

Bioengineering

First Advisor

Zhiwen Zhang

Abstract

This research looked at the metabolic response of Alcanivorax borkumensis in pyruvate-supplemented medium as well as its polystyrene microplastic degradation potential. The study used CO₂ analysis to confirm previous results on plastic digestion and discover new understanding into degradation kinetics and inhibitory pathways. A. borkumensis was cultivated in ONR7a medium with varied pyruvate concentrations (0.5%, 1%, and 2%) at 32 degrees C and 220 RPM. Polystyrene microplastics (≤5 mm) were introduced over five 24-hour experiments. Every four hours, the OD600 was used to track development, and the Zobell Marine agar plates streaked with bacteria at assigned time points verified viability. The controls were pyruvate only (positive), no carbon source (negative), and pyruvate with polystyrene (test). Goal one of confirming previous scientific results on plastic digestion was partially achieved. Although polystyrene-containing media saw development (especially in experiments 2, 4, and 5), the erratic OD600 and plating results made interpretation difficult, probably due to overlapping pyruvate metabolism. Goal 2 to identify new scientific insights on plastic digestion kinetics, inhibitory or competitive biopathways for synthetic polymer bond cleavage based on the analysis of CO2 was partially achieved. The optimal degradation kinetics developed between 8 and 12 hours of incubation with 1% pyruvate. The results suggest a hierarchical substrate use in which pyruvate enhances metabolism while suppressing the energy-intensive enzymatic pathways required for polymer bond cleavage. These findings highlight the need of pyruvate-free setups to definitively determine plastic mineralization and CO2 pathways. The most significant biomolecular new discovery in current experiment where unexpected bacterial growth in negative control (no pyruvate, no polystyrene), suggests A. borkumensis may possess an active CO₂ fixation pathway, which was also confirmed by the photo of the agar plates streaked with bacteria at assigned time points.

Download

Share

COinS