In an era where plastic pollution besieges our planet, ReMixHD emerges as a novel method for dealing with the growing problem. Our smart self-regulating symbiosis uses genetically engineered Pseudomonas bacteria to transform mixed plastic waste into valuable products. Furthermore, a digital twin of our symbiosis system will enable accurate predictions of the stability and scalability using genome-scale metabolic modeling. In doing so, we aim to establish Pseudomonas fluorescens as a new chassis organism for bioremediation. ReMixHD offers a new approach to mixed plastic recycling, paving the way toward sustainable development and environmental stewardship.
At this moment, the global recycling industry is grappling with an enormous challenge: the issue of mixed plastic waste i.e. plastic waste consisting of various oil-based polymers. As one expert in the field poignantly expresses:
“There is a colossal need for innovation concerning mixed plastics as current technologies fall short in comprehensively recycling them. They either undergo downcycling, incineration or end up in landfills. If ReMixHD can change this, I see both ecological and economic potential” (translated from German).
Countries with or without advanced recycling systems feel the effect of amassing plastic waste. Though
sophisticated recycling systems can deal with mixed plastic waste through pyrolysis, this method is
suboptimal due to its high energy demand, high greenhouse gas emission, economic infeasibility, and reliance
on major recycling infrastructure.
The ReMixHD platform tackles these challenges and presents an innovative recycling platform using
genetically modified Pseudomonas bacteria to upcycle mixed plastic waste to produce a usable product. It
will be the first system to address the mixed plastic waste problem while simultaneously decreasing
greenhouse gas emissions and operating in a decentralized manner. The platform's versatility would allow
countries like Germany to recycle mixed plastic waste and produce industrial compounds. At the same time,
communities in the global south could generate anything from pesticides to medication to animal food locally
by leveraging ReMixHD’s independence from major recycling infrastructure.
Through extensive research and interviews with experts, our project ReMixHD aims to tackle
environmental and infrastructural issues. A recycling expert commented:
“Your project could be a far more viable approach for recycling previously non-recyclable plastics than incineration plants” (translated from German)
While targets are ambitious, the ReMixHD system is an option for decentralizing mixed plastic waste recycling and fostering sustainable development, environmental stewardship, and innovation.
The ReMix system presents a novel solution for mixed plastic recycling by employing a self-regulating smart
symbiosis of genetically modified Pseudomonas bacteria. This innovative approach can adapt to the plastic
composition and synthesize a recombinant product. Through a co-culturing system, using distinct bacterial
strains to perform specialized tasks will increase the system's adaptability. Helper strains focus on
depolymerizing plastics into intermediates, while a main strain utilizes the intermediates for recombinant
product production. To ensure a stable and high-yielding co-culture, we custom-engineer an operon capable of
controlling the growth behaviors of the helper strains dependent on the plastic concentration and
intermediate levels. The bacterial strains' capabilities are selected based on local plastic compositions
and desired recombinant products.
A proof of concept for the ReMix system will be demonstrated in the laboratory by engineering a helper
strain capable of depolymerizing polyethylene (PE) and polyethylene terephthalate (PET) and a main strain
that can produce polyhydroxyalkanoates, a novel bioplastic (Gyung Yoon et al., 2012;
Werner et al., 2021; Montazer et al., 2019).
The custom operon will control the growth of the helper strain. A high plastic concentration will lead
to helper strain growth. At the same time, the resulting increase in intermediates will repress the growth
of the helper strain, thereby enabling the main strain to produce the recombinant product unimpeded. The
development of the operon system will fill a gap in control mechanisms for plastic degradation genes, which
are available in the iGEM part collection.
Our bioinformatics team developed a digital twin of our system, enabling us to predict product yields,
plastic degradation, co-culture stability, and the system's expansion to include other plastics and
products. Building on existing flux balance analysis models of P. fluorescens, which can predict a single
organism in a steady state, we aim to add dynamic and community flux balance analysis modeling (Huang and
Lin, 2020).
These additions allow us to virtually add new genes and metabolites to our platform giving us information on
future implementations and upscaling of the platform. These predictions also support our laboratory efforts
by suggesting changes needed to increase efficiency, metabolize additional plastics, and produce different
products.
Pseudomonas fluorescens is the ideal chassis bacterium for constructing the ReMixHD recycling system
due to its exceptionally diverse metabolism and inherent capability for natural plastic degradation. For
example, it can metabolize polymers like PE, polypropylene, polystyrene, and polyurethane, as well as
aromatic pollutants and halogenated hydrocarbons. These bacteria are also suited for specialized growth
media and bioremediation projects (Kyaw et al., 2012; Montazer et al., 2019; Mohanan et
al., 2020; Presentato et al., 2020; Shim et al., 2005; Wilkes and Aristilde, 2017; Wróbe et al., 2023;
Gyung Yoon et al., 2012).
While many Pseudomonas species exhibit remarkable metabolic potential, several of them are
pathogenic to humans, animals, or plants, rendering them unsuitable for bioremediation purposes. P.
putida and P. fluorescens are generally considered non-pathogenic, making them good candidates
for our project. While putida is widely used in a laboratory setting, P. fluorescens is
overlooked despite its metabolic potential. One significant advantage of P. fluorescens is its
ability to utilize nitrates as electron acceptors instead of relying solely on oxygen. This unique
characteristic is beneficial for large-scale implementation, as oxygen supply has been identified as a major
limiting factor in upscaling to industrial and remediation applications, thereby highlighting the value of
P. fluorescens in our chosen approach.
Bossis, E., Lemanceau, P., Latour, X., & Gardan, L. (2000). The taxonomy of Pseudomonas fluorescens and Pseudomonas putida: Current status and need for revision. Agronomie 20 (1), 51-63. https://doi.org/10.1051/agro:2000112.
Gyung Yoon, M., Jeong Jeon, H., & Nam Kim, M. (2012). Biodegradation of Polyethylene by a Soil Bacterium and AlkB Cloned Recombinant Cell. Bioremed Biodegrad, 3:4. https://doi.org/10.4172/2155-6199.
Huang, X. and Lin, Y.-H. (2020). Reconstruction and analysis of a three-compartment genome-scale metabolic model for Pseudomonas fluorescens. Biotechnology and Applied Biochemistry, 67: 133-139. https://doi.org/10.1002/bab.1852.
Kyaw, B. M., Champakalakshmi, R., Sakharkar, M. K., Lim, C. S., & Sakharkar, K. R. (2012). Biodegradation of low density polythene (LDPE) by pseudomonas species. Indian J Microbiol 52, 411–419. https://doi.org/10.1007/s12088-012-0250-6.
Mohanan Nisha, Montazer Zahra, Sharma Parveen K., & Levin David B. (2020). Microbial and Enzymatic Degradation of Synthetic Plastics. Front Microbiol, 11. https://doi.org/10.3389/fmicb.2020.580709.
Montazer, Z., Habibi Najafi, M. B., & Levin, D. B. (2019). Microbial degradation of low-density polyethylene and synthesis of polyhydroxyalkanoate polymers. Canadian Journal of Microbiology 65(3), 224-234. https://doi.org/10.1139/cjm-2018-0335.
Presentato, A., Lampis, S., Vantini, A., Manea, F., Daprà, F., Zuccoli, S., & Vallini, G. (2020). On the Ability of Perfluorohexane Sulfonate (PFHxS) Bioaccumulation by Two Pseudomonas sp. Strains Isolated from PFAS-Contaminated Environmental Matrices. Microorganisms, 8(1), 92. https://doi.org/10.3390/microorganisms8010092.
Shim, H., Hwang, B., Lee, S. S., & Kong, S. H. (2005). Kinetics of BTEX biodegradation by a coculture of Pseudomonas putida and Pseudomonas fluorescens under hypoxic conditions. Biodegradation 16, 319–327. https://doi.org/10.1007/s10532-004-1842-6.
Werner, A. Z., Clare, R., Mand, T. D., Pardo, I., Ramirez, K. J., Haugen, S. J., Bratti, F., Dexter, G. N., Elmore, J. R., Huenemann, J. D., Peabody, G. L., 5th, Johnson, C. W., Rorrer, N. A., Salvachúa, D., Guss, A. M., & Beckham, G. T. (2021). Tandem chemical deconstruction and biological upcycling of poly(ethylene terephthalate) to β-ketoadipic acid by Pseudomonas putida KT2440. Metabolic Engineering 67, 250-261. https://doi.org/10.1016/j.ymben.2021.07.005.
Wilkes, R. A., & Aristilde, L. (2017). Degradation and metabolism of synthetic plastics and associated products by Pseudomonas sp.: capabilities and challenges. J Appl Microbiol, 123: 582-593. https://doi.org/10.1111/jam.13472.
Wróbel, M., Szymańska, S., Kowalkowski, T., & Hrynkiewicz, K. (2023). Selection of microorganisms capable of polyethylene (PE) and polypropylene (PP) degradation. Microbiological Research 267. https://doi.org/10.1016/j.micres.2022.127251.