Microbiology Ph.D. Thesis Defense- Linda Zhong-Johnson (Sinskey& Voigt Labs)

Monday, April 1, 2024 2PM Room 68-181


Plastic production and pollution has become a global crisis, with 79% of waste plastics landfilled in 2015 and only 12% recycled, demonstrating the need for rapid improvements in waste management and recycling technologies. Poly(ethylene terephthalate) (PET) is a major plastic polymer that is heavily investigated for enzymatic recycling. The presence of the ester bond in the polymer allows hydrolysis via serine esterases, such as cutinases and lipases. However, little is known about the surface reaction and how biochemical behavior might differ on a 2D solid surface compared to solution phase. Consequently, traditional solution-phase biochemical models, such as Michaelis-Menten, may not be directly applicable to kinetics of these enzymes, as the catalysis is occurring under a heterogeneous phase. To improve the fundamental understanding of the enzymatic kinetics on the surface and derive an appropriate biochemical model for kinetic analysis, I develop a simple kinetic assay of PET biodegradation, a directed evolution assay to identify mutations that positively impact product formation rates at ambient temperature, and develop a novel biochemical model to analyze these mutations that fully describe the kinetic profiles observed for these enzymes.  Based on these studies, I show that macromolecular crowding is likely a major biochemical phenomenon governing enzyme kinetics on solid substrate surfaces, and that enzyme engineering to reduce crowding susceptibility will result in increased overall degradation rates.
Thesis Defense Committee Members: Prof. Cathy Drennan, Prof. Barbara Imperiali,  and Prof. Margaret Sobkowicz-Kline (UMASS, Lowell) Advisors: Prof. Chris Voigt, Prof. Anthony Sinskey