Diana I. Martínez-Tobón, Maryam Gul, Anastasia Elias, and Dominic Sauvageau.
Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta, Canada.
Biopolymers represent an interesting alternative to traditional plastics for a variety of applications; from packaging to medical devices. Even if most of them are readily degradable, this degradation can be slow and biopolymer accumulation in the environment is still a concern. Polyhydroxybutyrate (PHB) is a natural biodegradable polyester that is enzymatically degraded by PHB depolymerases (PhaZs) – enzymes produced by a variety of microbial strains. By studying the interactions between various PhaZs and PHB, we are able to better understand and predict the fate of PHB in the environment, develop strategies to reduce its environmental impact and develop PHB-based technologies for applications such as implants and biosensors. Bacteria isolated from various environments - like soil and see water – that displayed PhaZs activity or that had predicted PhaZ enzymatic activity – from genomic analysis – were screened for degradation of PHB.
The screening process was carried out using PHB pellets and films exposed to cell cultures and extracellular fractions. Thus far, of the bacterial strains tested, PhaZCte – produced by Comamonas testosteroni – has exhibited the highest enzymatic activity at 30°C. Further work has been completed at the molecular biology level in order to obtain the purified enzyme; a modified, functional, soluble version of PhaZCte containing a His6 tag (rPhaZCte) was successfully expressed in E. coli. These results set the basis for selecting strains with potential for scheduled biodegradation, along with the verification of PhaZ activity for strains that have only been predicted to produce PhaZ-like proteins. Furthermore, this study can aid in the design of PhaZ variants with enhanced performance under harsh conditions outside the optimal ranges for enzymatic performance.