Our project
Plastic pollution caused by the increasing use of non-biodegradable plastics has become a major global environmental concern. These plastics, often derived from petroleum, do not break down naturally in the environment and can persist for hundreds of years. As a result, they accumulate in landfills, oceans, and ecosystems, posing significant threats to wildlife, marine life, and even human health. Even when traditional recycling methods are applied, non-biodegradable plastics can degrade into microplastics: tiny plastic particles that contaminate water sources, enter food chains, and may carry harmful toxins.
In response to these growing problems, many scientists and environmental advocates are urging a shift away from petroleum-based plastics toward more sustainable alternatives. One promising option is the use of biodegradable plastics, such as polyhydroxybutyrate (PHB). PHB plastics are produced by microbial fermentation of organic materials and have the advantage of breaking down naturally in the environment without releasing toxic residues. They offer a potential solution to reduce the long-term environmental damage caused by conventional plastics.
However, despite their potential, PHB plastics are currently not as biodegradable in natural environments as initially hoped. While they are classified as biodegradable under industrial composting conditions, where temperature, moisture, and microbial activity are tightly controlled, PHB can take a significantly long time to break down in real-world settings such as soil, freshwater, or marine environments. This limits their effectiveness as a truly sustainable alternative to conventional plastics, especially considering that plastic waste often ends up in uncontrolled, open environments where ideal decomposition conditions are absent.
In addition to their limited environmental biodegradability, PHB plastics face economic challenges. The production of PHB is still considerably more expensive than the manufacturing of petroleum-based plastics like polyethylene or polypropylene. Polyester, in particular, remains one of the cheapest and most widely used synthetic plastics due to its low cost and scalability. This cost disparity makes it difficult for PHB and similar bioplastics to compete in the global plastics market, especially in large-scale, cost-sensitive industries like packaging and textiles.
As a result, while PHB represents a step toward more sustainable materials, it is not yet a fully effective replacement for conventional plastics. Continued research and innovation are needed to improve both its environmental performance and cost-effectiveness before it can serve as a viable large-scale solution to plastic pollution.
During a deep-sea expedition, our mentor, Assistant Professor Dr. Garza, employed metagenomic and metatranscriptomic analyses to identify a previously uncharacterized depolymerase and dehydrogenase pathway involved in the degradation of polyhydroxybutyrate (PHB). These enzymes have not yet been tested in vitro for their degradation efficiency or capabilities, which is the central focus of our project.
Currently, PHB plastics cannot be efficiently recycled or broken down under natural environmental conditions, limiting their viability as a sustainable alternative to conventional petroleum-based plastics. To address this, our project aims to genetically engineer the bacteria Escherichia coli (E. coli) and Alteromonas macleodii to express the newly discovered depolymerase and dehydrogenase genes.
If successful, these engineered organisms will be able to degrade PHB plastics efficiently and convert them into monomeric products. These monomers could then be used for the resynthesis of PHB, enabling a closed-loop recycling process that is more sustainable and effective than current recycling methods.
By demonstrating the feasibility of biologically driven PHB degradation and recycling, our work has the potential to significantly enhance the practicality of PHB as an alternative to petroleum-based plastics, contributing to long-term efforts to reduce plastic pollution globally.
Our project focuses on the genetic engineering of Escherichia coli (E. coli) and Alteromonas macleodii to express novel depolymerase and dehydrogenase genes, with the goal of enhancing the microbial degradation of PHB plastics. Engineered E.coli would allow degradation of PHB outside of marine environments, and although Alteromonas macleodii contains a natural PHB degradation pathway, we aim to see if this novel pathway provides any optimization. By enabling these organisms to express these key enzymes, we aim to significantly increase the breakdown efficiency of PHB, offering a potential biotechnological solution to mitigate plastic pollution.
A central objective of our work is to evaluate the in vivo expression and functional efficiency of these enzymes. This will help determine the feasibility of using engineered microbial systems for PHB degradation and inform future efforts toward sustainable plastic recycling.
The depolymerase and dehydrogenase gene sequences were obtained from the J. Craig Venter Institute (JCVI). Using a modular cloning approach, we incorporated JCVI's standardized promoter and terminator sequences to construct Level 0 (L0) and Level 1 (L1) plasmids. Multiple iterations of L1 plasmids were designed and assembled in an attempt to generate a functional Level 2 (L2) plasmid construct.
Despite extensive efforts, we were ultimately unable to successfully assemble a complete L2 plasmid in E. coli, and thus we moved on with tests with the L1. Using Alteromonas with knocked out depolymerase or dehydrogenase, we ran experiments to see if function could be restored with our novel depolymerase or dehydrogenase, respectively.
Kim, Jihyeon, et al. “Biodegradation Studies of Polyhydroxybutyrate and Polyhydroxybutyrate-Co-Polyhydroxyvalerate Films in Soil.” International Journal of Molecular Sciences, vol. 24, no. 8, 1 Jan. 2023, p. 7638, www.mdpi.com/1422-0067/24/8/7638#:~:text=The%20degradation%20was%20evaluated%20by, https://doi.org/10.3390/ijms24087638.
Pilapitiya, P. G. C. Nayanathara Thathsarani, and Amila Sandaruwan Ratnayake. “The World of Plastic Waste: A Review.” Cleaner Materials, vol. 11, no. 2772-3976, 1 Mar. 2024, p. 100220, www.sciencedirect.com/science/article/pii/S2772397624000042, https://doi.org/10.1016/j.clema.2024.100220.
Sosa, Alvaro Ríos, et al. “Genomic Analysis and Potential Polyhydroxybutyrate (PHB) Production from Bacillus Strains Isolated from Extreme Environments in Mexico.” BMC Microbiology, vol. 25, no. 1, 11 Jan. 2025, https://doi.org/10.1186/s12866-024-03713-7.