Abstract
Disclaimer: This project description is a draft written for the deadline of the Village selection. It is not the final form, and it will be extended and or changed in the future.
Cement production cement-based construction materials like concrete and bricks are responsible for around 8% of global anthropogenic CO₂ emissions (Kajaste und Hurme 2016). Multiple factors will lead to rising demand for cement in the coming decades and thereby increase the output of CO2 from this sector (Castro-Alonso et al. 2019; Lanjewar et al. 2025). At Pyricon, we are tackling this environmental challenge head-on by designing a sustainable, bio-based alternative to cement bricks. We engineer Bacillus subtilis to produce spider silk proteins and induce calcite precipitation, forming a sustainable biocement. Using a novel, PCR-free DNA assembly strategy, we overcome challenges in expressing highly repetitive silk genes. Our project not only enables eco-friendly construction materials but also introduces a versatile method for assembling complex synthetic DNA sequences.
Our Motivation
Climate change poses an unprecedented threat to society and the global economy. The latest Intergovernmental Panel on Climate Change (IPCC) report warns that the world is on track to far exceed the 1.5 °C target (Lee et al., 2023). CO₂ emissions are a key driver of global warming and continue to rise, with high-emission sectors like construction playing a particularly significant role. Cement and concrete production alone account for approximately 8% of anthropogenic CO₂ emissions (Kajaste & Hurme, 2016). In 2024, cement production contributed an estimated 1.5 gigatons of CO₂ (Global Carbon Project, 2024).
As populations grow and urbanization expands, demand for concrete is only increasing. Concrete is already the second most consumed material on Earth after water (Achal & Mukherjee, 2015; Farfan et al., 2019). Reducing its climate impact is therefore a pressing priority for sustainable development.
The Problem
The high CO₂ emissions of cement production result primarily from its energy-intensive manufacturing process, in which limestone is heated to approximately 1450 °C (Semugaza et al., 2023). Around 90% of total emissions from cement production are released during this stage. While 30% of these emissions are related to thermal energy generation (which could potentially be reduced through renewable sources like green hydrogen), 60% arise from the calcination of limestone (CaCO₃) – a chemical process that inherently emits CO₂ (Gjorv & Sakai, 1999; He et al., 2019).
Compounding the issue, concrete structures deteriorate over time due to environmental erosion (physical, chemical, and biological factors), leading to crack formation (Castro-Alonso et al., 2019). These cracks weaken mechanical integrity and durability, shortening service life and requiring additional cement for repairs or replacements.
Our Solution
We aim to address both the CO₂ emissions of cement production and the structural degradation of concrete by developing a novel bio-cement, a sustainable alternative that bypasses traditional high-temperature processing. Our approach leverages microbially induced calcite precipitation (MICP) in combination with synthetic spider silk proteins.
Microbially Induced Calcite Precipitation (MICP)
MICP is a naturally occurring process in which specific bacteria induce the precipitation of calcium carbonate. Promising results have already been achieved using MICP to create self-healing concrete and bioconsolidated sand (Anbu et al., 2016; Reeksting et al., 2020). However, the application of MICP faces limitations: for instance, in sand, particles may be too far apart for the calcium carbonate to effectively bond them.
Spider Silk as a Micro-Framework
To overcome this, we introduce synthetic spider silk proteins as a structural scaffold. The spider silk provides a micro-framework, enabling bacteria to anchor and enhancing the efficiency and consistency of mineral deposition.
Spider silk is known for its extraordinary mechanical properties - stronger than steel, lightweight, biodegradable, and highly elastic (Gosline et al., 1999; Vollrath & Knight, 2001). Its applications span biomedicine, aerospace, and biosensors (Ramezaniaghdam et al., 2022).
Our innovation lies in the use of pyriform silk, a lesser-studied type of silk used by spiders as attachment cement for anchoring webbing. This makes it an ideal candidate for bio-cement applications.
Future Outlook
Biotechnological production of spider silk has been limited by gene complexity, repetitive sequences, and low protein yields (Whittall et al., 2021). To address these challenges, we developed a novel hybrid cloning standard combining RFC1000 and RFC25 in a method we call Pyricloning. This enables the rapid buildup of repeat units from smaller building blocks into complete transcription units with tailored tags, transcription strength or other modifications.
References
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Anbu, Periasamy; Kang, Chang-Ho; Shin, Yu-Jin; So, Jae-Seong (2016): Formations of calcium carbonate minerals by bacteria and its multiple applications. In: SpringerPlus 5, S. 250. DOI: 10.1186/s40064-016-1869-2.
Castro-Alonso, María José; Montañez-Hernandez, Lilia Ernestina; Sanchez-Muñoz, Maria Alejandra; Macias Franco, Mariel Rubi; Narayanasamy, Rajeswari; Balagurusamy, Nagamani (2019): Microbially Induced Calcium Carbonate Precipitation (MICP) and Its Potential in Bioconcrete: Microbiological and Molecular Concepts. In: Front. Mater. 6, Artikel 126. DOI: 10.3389/fmats.2019.00126.
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Reeksting, Bianca J.; Hoffmann, Timothy D.; Tan, Linzhen; Paine, Kevin; Gebhard, Susanne (2020): In-Depth Profiling of Calcite Precipitation by Environmental Bacteria Reveals Fundamental Mechanistic Differences with Relevance to Application. In: Applied and environmental microbiology 86 (7). DOI: 10.1128/AEM.02739-19.
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