Abstract

Microplastics are increasingly widespread and are now found in the environment, the food chain, and the human body. Although the full extent of the impacts of microplastics is unknown, research indicates that they increase the likelihood of heart attack, stroke, or death. The need to remove microplastics from the environment has never been more urgent. At the same time, the U.S. Geological Survey reports that 1 billion tons of limestone are quarried annually in the United States alone.

Our team aims to address both of these issues by engineering E. coli to co-express plastic-binding curli fibers and a biomineralization pathway, thereby capturing microplastics in in situ limestone formations. In particular, we have tested two different microbially induced calcite precipitation (MICP) pathways for biomineralization: a carbonic anhydrase-catalyzed pathway and a urease-catalyzed pathway. Our resulting aggregate could be utilized to both immobilize harmful microplastics and replace non-renewable resources like sand for construction and backfilling projects.

For each pathway, we successfully developed ODE-based software tools to model levels of CaCO3 production based on concentrations of each component. We were able to generate samples of biomineralized solids using a urease-based pathway around sand with microplastic contamination utilizing S. pasteurii, a natural biomineralizing bacteria. Additionally, we were able to diagnose protein expression issues in a curli and carbonic anhydrase fusion protein, with the issue lying in the protein transport or oligomerization stage, thus providing a potential path forward for successful curli fiber expression.

Throughout the process, we consulted with over 10 experts in the field, ran classes and workshops with over 150 students, and translated materials into over 4 languages. We hope to not only create a synthetic biology solution but also effectively integrate said solution into the community through both education and outreach.

Issue

With microplastics now found in human bloodstreams, brains, and the food chain, the need for synthetic biology solutions like ours has never been more urgent. Jambeck et al. (2015) find that 5 to 12 million tons of plastic enter the ocean yearly, decomposing into microplastics and harming both the environment and humans. An estimated 7.2 trillion microplastic particles enter San Francisco Bay annually through urban stormwater runoff, which is equivalent to enough particles to carpet the Golden Gate Bridge three times over each year (Ross et al., 2023). Efforts that reclaim plastics from the environment often end up in landfills and wastewater treatments, where the microplastics leak back into the environment (Landfills as a Major Point Source for Microplastic Pollution, n.d.). These microplastics then wreak havoc in a number of ways.

Microplastics in the environment have a drastic impact. Zhu et al. (2025) find that current exposure to microplastics is responsible for a 7 to 12% reduction in photosynthesis in terrestrial plants globally.

Microplastics travel up the food chain, ultimately ending up in the human body. “Plastics love fats, or lipids, so one theory is that plastics are hijacking their way with the fats we eat which are then delivered to the organs that really like lipids — the brain is top among those” says Matthew Campen, Regents’ Professor and professor of pharmaceutical sciences at the University of New Mexico in Albuquerque. A 2024 study he coauthored found that across 12 autopsy samples, microplastics made up an average of 0.48% brain mass, 50% higher than samples taken earlier in 2016 (Nihart et al., 2025).

At the same time, the Willett and U.S. Geological Survey (2024) reports that 1 billion tons of limestone are quarried yearly in the United States alone.

Current Solutions

A number of solutions exist for microplastic capture, a few of which we describe here. “Microcleaners,” developed by Haeleen Hong et al. at NC State, are comprised of soft dendritic colloids (SDCs) and can be used as an efficient method for finding, collecting, and removing microplastics from oceans. The microcleaners concentrate into “pellet” agglomerates and have the ability to self-propel via releasing surface active compounds which induce propulsion through the Marangoni effect. While traveling across the water, the microcleaners coil then disperse the SDCs, which sediment and “capture” the microplastics, and the two combined perform transverse active motion and float up to the surface.

A number of companies even commercialized microplastic binding solutions, such as Polygone Systems which uses such methods for water filtration and Seabin, which runs on funding from company donors. A common thread is that while a number of companies are able to capture microplastics, few companies describe solutions to handle microplastics after their capture.

Currently the best solutions for handling plastics after collection tend to involve some kind of plastic degradation or recycling. For instance, Yip et al. (2024) describe microbial solutions to break down polyethylene terephthalate (PET), one of the most common plastics used today. There are microbes and insects that are able to metabolize plastics initially believed to be non-biodegradable, albeit at a slow rate. Solutions to recycle individual plastics, such as PET and HDPE, do exist and are often used (Almack, 2023).

One big issue is the purity of the plastics to be recycled in these systems. Yip et al. (2024) note that PET is more susceptible to biodegradation than most plastics due to hydrolysable ester bonds. The same problem exists with recycling. While certain kinds of pure plastics, such PET and HDPE, can be recycled, mixed plastics are rarely, if ever, recycled (Almack, 2023).

This creates a disconnect between systems that collect mixed plastics like Seabin and Polygone, and forms of plastics disposal, which we hope to bridge with our project.

Our Solution

Our iGEM team is engineering E. coli to co-express plastic-binding curli fibers and a biomineralization pathway in order to capture microplastics in in situ limestone formations.

We experiment with two known pathways for microbially induced calcite precipitation (MICP): a carbonic anhydrase-catalyzed pathway and a urease-catalyzed pathway. While carbonic anhydrase has the benefit of not producing ammonium byproducts, the urease pathway is known to induce greater amounts of mineralization.

The product created by our engineered E. coli can then replace non-renewable resources like sand for construction and backfilling projects. We intend for our solution to be used on microplastics captured by groups like Seabin and Polygone, removing the risk factor of releasing genetically modified E. coli into the wild.

Impacts

We can estimate the potential impact of our solution by seeing what similar systems have accomplished in nature.

Most soil microplastics stay near the surface where roots and fauna interact with them, thus making immobilization a high-leverage mitigation measure. Using carbonic anhydrase, researchers have precipitated CaCO₃ that biocements soil, raising unconfined compressive strength to ~1 MPa through adding ~2.8% CaCO₃, with SEM/Raman-confirmed calcite coatings that can encapsulate particulates (Mwandira et al., 2024). By closing pore throats, biocementation reduces permeability (by up to ~98%), curbing vertical migration and runoff vectors for microplastics (Arab et al., 2021). Carbonic anhydrase pathways do not rely on urea hydrolysis, thus avoiding the ammonium by-products characteristic of urease-based MICP (Gilmour et al., 2024; Arias et al., 2025). In short, locking microplastics into a CaCO₃ matrix is a known solution for reducing microplastic exposure dramatically, turning contaminated topsoil from a vector into a stable sink.

Environmental:

Preventing microplastics from being released into the environment has the potential to make a big impact. Zhu et al. (2025) find that a 13% reduction in total microplastics could reduce photosynthetic losses by nearly 30%, generating an additional 22 to 116 MT·y−1 in crop production. Such an increase in photosynthesis, if extended across all forest biomass, would serve to remove approximately an additional 230 million metric tons of CO2 from the environment (Harris et al., 2021). This equates to a 0.5% reduction in global CO2 emissions per year (World Meteorological Organization, 2024).

Human Health:

Microplastics are not inert passengers in mammals: they enter circulation, lodge in tissues, and are correlated with adverse outcomes. Plastic particles were detected in 17/22 healthy adults’ blood at a mean ~1.6 µg/mL (≥700 nm; PET, PE, styrenics among the polymers), demonstrating systemic exposure in humans (Leslie et al., 2022). In a cardiovascular cohort of 304 patients undergoing carotid endarterectomy, those with micro/nanoplastics embedded in plaques had a 4.53× (95% CI 2.00–10.27) higher hazard of stroke, myocardial infarction, or death over ~34 months, linking tissue‐level plastic burden to clinical outcomes (Marfella et al., 2024). Independent clinical work in acute coronary syndrome similarly associates higher blood microplastic loads with more complex vascular pathology and immuno-inflammatory shifts (e.g., IL-6, NK/B-cell changes) (Yang et al., 2024). Mechanistically, animal and cellular studies converge on oxidative stress, barrier dysfunction, and metabolic disruption as plausible pathways (Kadac-Czapska et al., 2024). Critically, dialing exposure down may not quickly reset biology: in mice exposed long-term (21 weeks) and then taken off microplastics for 4 weeks, lipid-metabolic and microbiome disturbances showed only partial recovery, especially after higher doses (Deng et al., 2025). Together, the evidence argues for upstream exposure reduction—and for practical strategies like immobilization at the source—to limit human contact and risk.

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