Description

The Far-Reaching Consequences of CO₂ Pollution: Impacts on the Global Environment

The intensified carbon dioxide (CO₂) pollution has caused critical damage to the environment, including climate change, ocean acidification, and worldwide ecosystem disruption. Accounting for two-thirds of greenhouse gas emissions, CO₂ plays a crucial role in exacerbating climate change by absorbing and re-radiating heat from the Earth's surface, thereby maintaining global surface temperatures (Overview of Greenhouse Gases, 2025). A surging carbon dioxide concentration intensifies the greenhouse effect, resulting in a rise in global temperatures (Lindsey, 2025). For instance, for the last thirty years, Taiwan’s temperature has been rising by a rate of 0.30°C every decade, which was 0.09°C higher than the global rate. However, although increasing carbon dioxide provides the global warming baseline, countries such as Taiwan warm faster due to urban heat islands and geographical locations (Center Weather Bureau, 2021).

The phenomenon of the intensified greenhouse effect is due to molecular absorption, which depends on specific wavelength ranges. For example, diatomic molecules like oxygen (O₂) and nitrogen (N₂) absorb high-energy radiation with wavelengths at 200 nanometers. The simple composition of diatomic molecules restricts their movements and thus the range of wavelengths they can interact with (Fecht, 2021). On the other hand, greenhouse gases like carbon dioxide (CO₂), which consist of two or more different atoms, possess a more complex structure. The complexity allows a larger variety of movement and vibration modes, which enables them to absorb a larger energy range between 2,000 and 15,000 nm (Fecht, 2021). After absorbing infrared energy, these gases re-emit it in all directions, with half of it directed back toward Earth’s surface as heat. This results in elevated temperatures and extreme weather events, including droughts, flooding, and heat waves.

The global average atmospheric CO₂ level reached 419.3 ppm in 2023, marking a 2.8 ppm increase from 2022 and the 12th consecutive year where CO₂ levels rose by more than two ppm, according to the National Oceanic and Atmospheric Administration (NOAA)’s Global Monitoring Laboratory (Stein, 2024). The annual emissions of CO₂ rose from 11 billion tons per year in the 1960s to 36.6 billion tons in 2023, which has caused significant problems, including global warming and climate change, detrimental to the Earth (Lindsey, 2025).

Additionally, CO₂ and water react to form a weak acid, carbonic acid (H₂CO₃), which significantly decreases the pH level of the ocean (Ocean Acidification | National Oceanic and Atmospheric Administration, n.d.). Ocean acidification has dramatically impacted the marine ecosystem, particularly for calcifying organisms, as maintaining their shells and skeletons becomes increasingly challenging. These facts underscore the urgent need to address CO₂ emissions, considering their irreversible environmental impacts in threatening biodiversity, marine ecosystems, and global ecological balance.

Firstly, the team wants to discuss the different factors causing the elevation of CO₂:

Fossil Fuel Combustion Emits Various Air Pollutants, Including the Primary Greenhouse Gas, CO₂

The combustion of fossil fuels, such as coal, oil, gasoline, diesel fuel, and natural gas, for industry, transportation, heating, and electricity generation, is the primary cause of air pollution worldwide (Figure 2) (Types of Pollutants, n.d.). Byproducts are released into the atmosphere when fossil fuels are burned. CO₂, a significant greenhouse gas, is the main product emitted during the processes. In addition, nearly all emissions of sulfur dioxide and nitrogen oxides, as well as 85% of airborne respirable particle pollution, are produced by fossil fuel combustion. Mercury, black carbon, polycyclic aromatic hydrocarbons, PM 2.5, toxic metals, and volatile compounds that contribute to ground-level ozone are also released during the process (Perera, 2017; Maciejczyk et al., 2021).

This increasing trend in carbon dioxide concentration resulted from the combustion of fossil fuels for energy use over the centuries. Accordingly, industrial emissions from the energy sector contribute to 75.7% of global greenhouse gas emissions. In 2022, Taiwan’s energy sector consistently remained the largest source of greenhouse gas emissions, accounting for around 94.61% of total emissions (GHG Inventory, 2022).

Specifically, in 2019, Taiwan consumed 4.81 × 10¹⁸ joules of energy originating from fossil fuel combustion, accounting for around 1% of the world’s total energy consumption. This massive consumption of fossil fuels results in the substantial release of air pollutants like greenhouse gases, including CO₂ (Tsai et al., 2021).

Deforestation, a Driver of Atmospheric Carbon Dioxide, Causes Climate Impacts

Other than fossil fuel combustion, deforestation is also a massive source of carbon dioxide pollution (Figure 2). It emits approximately 2.1 billion tons of carbon dioxide per year over five years from 74 developing nations (Pearson et al., 2017; De Sy et al., 2019). In the 2000s, the world's forest area experienced a loss of about 5.2 million hectares, with the most being in South America (Chakravarty et al., 2012). Deforestation contributes to the accumulation of carbon dioxide in the atmosphere by releasing the carbon sequestered in living biomass into the atmosphere through decomposition and combustion, while restraining the photosynthesis process due to reduced tree cover.

The Industrial Sector Drives Carbon Dioxide Accumulation

Another significant source of carbon dioxide pollution is industrial processes. Industrial processes emit greenhouse gases, including carbon dioxide, methane, nitrous oxide, and fluorinated gases (Figure 2). Specifically, they contribute to the annual emissions of roughly 50 billion metric tons of carbon dioxide worldwide. In Taiwan, industrial processes are one of the primary sources of greenhouse gas emissions (W. Tsai, 2020). While industrial processes only account for 5.34% of carbon dioxide emissions in Taiwan in 2017, they still surpass the agricultural sector (0.01%) and the waste sector (0.04%), with only the energy sector having higher emissions of 94.61% (“2019 Republic of China National Greenhouse Gas Inventory Report,” 2019).

Since Taiwan is responsible for producing a sizable portion of global electronics components, it has industrial processes that contribute significantly to carbon dioxide emissions. Solely from electrical and electronic machinery, 25655 thousand tonnes of CO₂ were released in Taiwan in 2016, which is about 19.7% of CO₂ emissions from industrial processes (Figure 1) (Chou et al., 2019). For Taiwan, though, this also offers a big opportunity. By investing in sustainable manufacturing practices, Taiwan can overcome potential carbon lock-in, achieve its carbon-reduction objectives of reducing net greenhouse gas emissions by 28% by 2030, and lead the world in taking environmental responsibility (Roussilhe et al., 2022; Council, 2015). Carbon dioxide emissions from industrial processes in Taiwan are on a decreasing trend, where the emissions in 2022 decreased by 28.37% compared to 2005 (GHG Inventory|Taiwan 2050 Net-Zero, n.d.). A summary of processes contributing to increased CO₂ emissions can be found in Figure 2.

Figure 1: Carbon dioxide emissions from different industrial processes in Taiwan in 2016 (Chou et al., 2019)

Figure 2: The far-reaching consequences of CO₂ pollution

CO₂ Pollution Impacts Crop Productivity, Crop Quality, and Food Security

To highlight the rising concentrations of CO₂ in the atmosphere and their significant impacts on the global food system, the team explores how climate change alters crop productivity and quality, thereby threatening food security.

CO₂ Accumulation Affects Crop Growth

Rising CO₂ can prompt plant growth and temporarily uplift crop yield; these apparent benefits often mask negative trade-offs (Figure 3) (Myers et al., 2014). Higher temperatures shorten the growing season and accelerate the physiological maturity of crops (Zhu et al., 2023). Yet, this leads to a decrease in nutritional quality and lower yields because plants collect sunlight throughout the growing season, storing the necessary energy and nutrients. If the plant grows too quickly, it won’t have enough time to accumulate the essential nutrients for growth, resulting in a lower grain yield compared to a more extended development period.

Simulated crop yield losses may range from 7% to 23% under severe climate change scenarios. Between 1980 and 2015, high drought caused a decrease of up to 20% in wheat production and 40% in maize (Kim & Lee, 2023). Research has shown that a 1°C increase in temperature results in a yield drop of 7.5% in maize, 6% in wheat, and 6.8% in rice (Hu et al., 2024). The production of maize crop yields is expected to decline by 24% by 2030, according to NASA (Gray, NASA’s Earth Science News Team, 2023). Nevertheless, the negative impacts of overwhelming CO₂ emissions easily outweigh the above benefits.

CO₂ Accumulation Affects Crop Quality and Nutrition

Nutrition is fundamentally about nourishing the body and supporting overall well-being. Currently, public-health agencies strongly promote choosing nutrient-dense foods such as fruits, vegetables, and lean proteins over highly processed alternatives. Despite the consensus that thoughtful diet choices will result in higher nutrient intake, the nutritional quality found in crops that are not heavily processed has decreased substantially due to the increase in carbon dioxide emissions (Figure 3) (Kidane et al., 2025). Some influences on nutritional quality could result in “hidden hunger,” as even if people consume enough calories, they may still suffer deficiencies in essential nutrients like zinc, vitamins, and protein (Kam, 2025).

Atmospheric CO₂ levels of approximately 550 ppm predicted for the mid-21st century may cause crops to lose crucial nutrients, resulting in zinc deficiency for 150-200 million people and protein deficiency for approximately 150 million people (Sneed, 2024).

According to an article published in the Plant Journal, rising carbon dioxide concentrations compromise the nutritional quality of crops, not only by increasing carbohydrate content but also by diluting key nutrients essential to human health, particularly protein, iron, and zinc (McGrath & Lobell, 2012). The changes in nutritional quality are evident through a meta-analysis, which found that protein levels decreased by approximately 10%, iron by 16%, and zinc by about 9% under higher CO₂ conditions (Figure 3) (Schmitt, 2024).

People’s nutrition resources come from crop productivity. As food production decreases, global food supplies also decrease, leading to increased malnutrition. Especially in regions with current nutrient deficiencies, where their nutritional quality deteriorates more, and they are disproportionately affected (van Dijk et al., 2021). According to van Dijk, the total food demand is likely to increase by around 35 to 56 percent between 2010 and 2050 (van Dijk et al., 2021). This means that if the demand for food increases, the production of food must increase to decrease malnutrition. An outline of CO₂ pollution impacts on crop quality and nutrition is presented in Figure 3.

Figure 3: CO₂ accumulation affects crop quality and nutrition

CO₂ Pollution and Public Health: Linking Atmospheric Changes to Respiratory and Cardiovascular Outcomes

As of 2024, global CO₂ concentrations have increased to 422.7 parts per million (ppm), marking a new high for atmospheric CO₂ concentrations (Lindsey, 2025). While traditionally viewed only as a climate issue, excess atmospheric CO₂ has been linked to a significant exacerbation of respiratory and cardiovascular diseases, an increase in heat-related illnesses, and numerous indirect effects on public health (Figure 4). As the primary driving source of climate change, CO₂ intensifies environmental factors that directly harm respiratory and cardiovascular health.

In particular, the escalating air pollution and extreme weather events have been identified as risk factors that exacerbate chronic respiratory diseases (CRD), causing severe public health burdens worldwide towards the specific group of patients with asthma and COPD (Figure 4) (Xu et al., 2025). The CRD predominantly includes "chronic obstructive pulmonary disease (COPD) and asthma,” which are associated with environmental factors such as CO₂, adverse meteorological conditions, extreme temperatures, and atmospheric allergens, all of which increase the risk of it (Xu et al., 2025).

Specifically, the most commonly contacted air pollutants can cause extreme respiratory diseases. For instance, the increased levels of particulate matter (PM), a common air pollutant formed through chemical reactions exacerbated by higher temperatures, result in aggravated asthma and COPD through prolonged exposure.

Additionally, as heatwaves occur more frequently due to rising CO₂ levels, this in turn contributes to serious health concerns, particularly in metropolitan locations where pavement and buildings trap heat (Z. Zhu et al., 2024). Dehydration, heat exhaustion, and heatstroke are among the more prominent heat-related ailments that disproportionately impact vulnerable populations, including children, the elderly, and outdoor laborers (Figure 4). According to the World Health Organization (WHO), an estimated 250,000 additional heat-related deaths will occur each year due to respiratory issues resulting from climate change, underscoring the pressing need for public health awareness and climate action (Climate Change, n.d.). An overview of connections between CO₂ pollution and public health is displayed in the figure on the right (Figure 4).

Figure 4: CO₂ pollution and public health: linking atmospheric changes to respiratory and cardiovascular outcomes

A Review of Conventional Strategies Mitigating CO₂ Pollution: Strengths and Limitations

Afforestation and Reforestation

One approach to mitigating carbon dioxide pollution is afforestation, which involves planting trees in areas that were previously not forested. Forests were estimated to have removed an average of 2 billion metric tons of carbon from the atmosphere per year since 2000 (Melillo, 2021). Research suggests that aforested areas can collect up to 24% more carbon than naturally occurring forests (Balu, 2024).

Another current solution is the establishment of mangrove forests. Mangrove forests have been proven to be effective at carbon sequestration in coastal regions, as they accommodate large carbon stocks, enable long-term carbon storage, and displace organic carbon from the coastal zone to the offshore and ocean areas (Choudhary et al., 2024). Accordingly, 88% of the carbon captured by mangroves is stored below the water surface, particularly within the top 3 meters of sediment, offering a stable and effective carbon storage system (Apple, 2019).

However, afforestation and mangrove restoration can harm local biodiversity and often require ongoing awareness, maintenance, and protection to remain effective (Wilson & Forsyth, 2018). Planting non-native tree species could pose a threat to the biodiversity of local ecosystems, increase wildfire incidences, and deplete water resources (Sustainability, 2023).

Additionally, due to land use demands and ecological constraints, both methods are time-consuming and require meticulous oversight, so they are not always feasible in achieving broader climate mitigation goals (Wilson & Forsyth, 2018). Land-use conflicts regarding agricultural and urban development could also hinder the implementation of afforestation and reforestation (Sustainability, 2023).

Renewable Energy Adoption and Carbon Capture and Storage (CCS)

The accelerating pace of climate change has transformed the shift to low-carbon energy from a policy aspiration into an economic inevitability. Utility-scale solar photovoltaics, onshore and offshore wind, modern hydro, and sustainably sourced bioenergy now drive global capacity growth.

The International Energy Agency (IEA) projects approximately 585 GW of additional renewable capacity in 2024, accounting for more than 90% of all new power additions, with two-thirds of this capacity supplied by solar energy (Edmond, 2025). Rapid learning curves have driven down levelized costs to such an extent that 86% of the capacity added in 2022 generated electricity more cheaply than the most competitive fossil-fuel alternative, resulting in approximately US$520 billion in fuel expenditure savings (Energy, 2018). Renewables already supply over 40% of global electricity, and China alone is on track to reach ≈ 1.8 TW of installed renewable capacity by 2025 (Figure 5) (Graham et al., 2025).

Yet aggregate statistics obscure significant caveats. For example, intermittent generation still overwhelms the grids where there isn't enough battery, pumped-hydro, or long-duration storage for curtailment and capacity-credit concerns (Figure 5). In addition, critical minerals like lithium and cobalt, and rare earth elements, experience trading volatility and geopolitical centralization. Moreover, renewable energy facilities depend on weather; thus, they are subject to weather events and climate change fluctuations, which lead to geographical constraints and intermittent, unreliable power generation. Finally, less-developed countries often can not afford to employ alternative energy on a large-scale operation due to their financial constraints.

Decarbonising hard-to-abate sectors, cement, steel, petrochemicals, and long-haul transport, therefore, requires tools beyond electrification. Carbon Capture and Storage (CCS) captures carbon dioxide at point sources or from the ambient air, compresses it, and sequesters it in deep saline aquifers or depleted oil and gas reservoirs. Despite five decades of pilot work, only ~45 Mt CO₂ yr¹ are captured worldwide, while net‑zero pathways typically call for ≥ 1 Gt CO₂ yr¹ by 2030 (Nations, n.d.). The prominent hurdles for implementation include high capital and operating costs, as post-combustion capture ranges typically from US$60 to US$120 per ton of CO₂ (Rodwell, 2021).

Another issue arises when discussing storage liability and monitoring, as the long-term integrity of injection sites must be demonstrated over centuries, necessitating robust regulatory frameworks to ensure their stability (Figure 5). Specifically, CCS, with its injection of CO₂ into geological platforms, could harm the environment through leakages into the groundwater or the atmosphere (Veloso, 2023).

Despite these challenges, CCS offers strategic value where process chemistry generates unavoidable carbon dioxide, and emerging negative-emission variants, such as Bioenergy with CCS (BECCS) or Direct Air Capture, could offset residual emissions if cost and energy barriers are overcome (Martinot, 2021). Neither pillar is sufficient alone: renewable energy is constrained by storage, siting, and materials, while CCS cannot viably substitute for an expansive clean-power build-out. Figure 5 below depicts the key image of renewable energy adoption and carbon capture and storage (CCS).

Figure 5: Renewable energy adoption and carbon capture and storage (CCS)

Governmental Policy and Regulatory Measures

To comply with Taiwan’s 2050 goal of net-zero emissions, the Taiwanese government proposed the “Climate Change Response Act” on December 29, 2023 (Revised Enforcement Rules of “Climate Change Response Act” Announced, n.d.). It strengthens the previous version of policies and enhances carbon reduction in the public through increasing government responsibility and transparency. Furthermore, this legislation introduces a carbon pricing mechanism applicable to major emitters, including the manufacturing and energy sectors. Enforced by the Environmental Protection Agency (EPA), the Response Act requires industries to track, disclose, and reduce their CO₂ emissions, encouraging the implementation of low-carbon technologies (Figure 6).

Specifically, the revised enforcement rules instigate a precise mechanism for carbon pricing. For instance, the collection of carbon fees serves as an additional role to the central competent authority’s responsibility to oversee the greenhouse gas (GHG) emissions. While supplementary fees are garnered, the central government is also required to manage the “GHG Management Fund,” indicating that the carbon fees will be allocated to a dedicated fund (Revised Enforcement Rules of “Climate Change Response Act” Announced, n.d.). However, carbon tax proposals face significant political and societal opposition in various regions and industries, with influential fossil fuel sources or extensive coal, oil, and gas usage (Omolere, 2024).

Aside from the five-year cycle of redefining goals and programs, the “Taiwan’s Emissions Data System (TED),” established in 1992, is updated biennially, covering the estimation of emissions from various regions of the country as part of an analysis of the area’s air quality. Lastly, the rule demands the disclosure of relevant meeting information to the public within 10 days for central action programs and within 7 days for local executive plan discussions, facilitating public inquiry and transparency. Thus, the current proposed Response Act strengthens the previous regulations, ameliorating Taiwan’s CO₂ emissions more comprehensively.

Another governmental regulatory method is the cap and trade system, a program issued to “cap” the level of carbon emissions in industrial activity through the allocation and trading of permits. Opponents of the system argue that emission credit purchases and fines for exceeding the cap limit are often cheaper than renewable technology conversions, resulting in an ineffective incentive and stagnation of change. In addition, lax monitoring and surveillance enable companies to circumvent the cap and trade system. Finally, there is no global consistency in the system, given the varying standards and maximum “caps” for carbon emissions in countries.

Concludingly, the revisions on the “Climate Change Response Act” signify Taiwan's commitment to a more proactive, legally backed, and collaborative approach to climate change, integrating industrial optimization with comprehensive regulatory and economic measures to drive CO₂ reduction across various sectors (Figure 6).

The renewable energy, carbon capture and storage, governmental regulations, and reforestation plans to mitigate carbon emissions, while they often provide adequate short-term results, their solutions usually fall short due to long-term complications that each single facet can not solve (Figure 7). Therefore, our project aims to approach reducing carbon emissions in a well-orchestrated method to ensure stability and efficiency.

Figure 6: Strategies to achieve the net-zero 2050 goal

Figure 7: Why conventional climate tools fall short

Optimizing Carbon Fixation: The Complex CO₂-Concentrating Mechanism (CCM) in Cyanobacteria

Cyanobacteria, also known as blue-green algae, are organisms responsible for performing oxygenic photosynthesis. Their natural cellular configuration, with evenly distributed chlorophyll (predominantly in the chloroplasts) throughout the cell, has significantly contributed to global carbon cycling (Demoulin et al., 2019). In the heart of photosynthesis in cyanobacteria, or all other photosynthetic organisms, ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) acts as the enzyme that initiates the carbon fixation process in the Calvin cycle by catalyzing the reaction between CO₂ and ribulose-1,5-bisphosphate (RuBP), a five-carbon sugar with two phosphate groups attached (Fig.8; Galmés et. al., 2016). However, RuBisCO’s efficiency can be limited by its affinity for oxygen. When exposed to low CO₂ or warm environments, the oxygen molecules’ ability to bind to their active site initiates another process known as photorespiration, causing carbon fixation in cyanobacteria to become constrained based on the environment. Photorespiration occurs when RuBisCO binds O₂ to RuBP, a 5-carbon sugar, in an oxygenase reaction. This produces 3-PGA and the two-carbon compound phosphoglycolate, which cannot enter the Calvin Cycle, resulting in energy loss. The affinity of RuBisCO for O₂ increases with temperature, further complicating carbon fixation under warm conditions (Galmés et. al., 2016; Shi & Bloom, 2021).

Figure 8: The overview of the carboxysome in the Cyanobacteria

To overcome this inefficiency, cyanobacteria utilize a CCM (CO₂-concentrating mechanism), much of which depends upon cell architecture components, with the carboxysome being an integral component (Burnap et al., 2015). The CCM’s essential purpose is to accumulate bicarbonate ions and convert them to CO₂ at the site of carbon fixation. However, despite CO₂’s ability to diffuse freely across membranes, any CO₂ can also diffuse easily out of the cell, reducing the local CO₂ concentration around RuBisCO and limiting its carboxylation efficiency (Kupriyanova et al., 2013). However, a mechanism evolved that permitted the cyanobacteria to import inorganic carbon actively, most often in the form of bicarbonate, and then transform it back into CO₂ within the carboxysome via carbonic anhydrase. This allows for CO₂ concentration at RuBisCO, not the entire cytoplasm. Researchers suggest that the bicarbonate ions, which preserve the functionality of the CCM, derive from two potential sources. First, the reaction from CO₂ to H₂CO₃ is spontaneous and occurs reversibly when CO₂ is hydrated, with subsequent dissociation to HCO₃^- and H⁺; it is this HCO₃^- that can be imported via active transporters such as BCT1 (Doyle & Cooper, 2023). Second, for some cyanobacteria, periplasmic carbonic anhydrases speed the conversion of CO₂ to HCO₃^-, providing a source for BCT1 and other channels to import into the cytoplasm (Marcus et al., 2005). The methods and significance of the bicarbonate ion uptake of cyanobacteria will play an essential role in the CCM pathway.

Component 1: HCO₃^- Uptake Systems
One crucial HCO₃^- transporter is Bicarbonate Transport 1 (BCT1). It is located on the membrane between the periplasm and the cytoplasm, which is the inner cell membrane of cyanobacteria. Function-wise, BCT1 transports HCO₃^- into the cytosol using energy from two ATPases contributed by cmpC and cmpD (Rottet et al., 2024). Since the BCT1 transporter in wild-type cyanobacteria is normally induced under low-carbon conditions, placing cyanobacteria in high-CO₂ fixation chamber would repress its activity, limiting bicarbonate uptake capacity (Shi & Bloom, 2021). Therefore, our team’s goal is to engineer the BCT1 transporter under a light-inducible promoter, allowing its expression independently of carbon levels. This strategy not only boosts bicarbonate ion transport but also allows continuous activation in high CO₂ environments, thereby enhancing carbon fixation.

Component 2: CO₂ Uptake Systems
In addition to HCO₃^- uptake, cyanobacteria possess CO₂ hydration systems that convert CO₂ to HCO₃^- in the cytosol to support carbon accumulation. This is achieved via the thylakoid NDH complexes. These membrane complexes capture diffused CO₂ and prevent it from escaping the cell, minimizing carbon loss (Shibata et al., 2001).

Component 3: Carboxysomes
After being captured, HCO₃^- transported into the cytoplasm will diffuse into carboxysomes, which are specialized protein microcompartments that encapsulate RuBisCO and carbonic anhydrase (CA) (Rottet et al., 2024). Within carboxysomes, carbonic anhydrase catalyzes the reversible hydration of CO₂ to HCO₃^- to overcome CO₂ limitation, especially in environments with low CO₂ concentrations. CO₂ is concentrated inside the carboxysome to reduce oxygen binding to RuBisCO. As HCO₃^- enters the carboxysome, it is converted into CO₂ through CA, saturating RuBisCO's CO₂ binding sites and minimizing photorespiration (Mukherjee et al., 2025).

Together, as shown in Fig. 9, these integrated components of the CCM enable cyanobacteria to maintain efficient photosynthesis under low external CO₂ conditions. In our project, we focus on optimizing the expression of the cmpABCD operon, which encodes the BCT1 transporter to increase intracellular HCO₃^- accumulation. Through this approach, we aim to improve the overall efficiency of the CCM and increase CO₂ in the carbon fixation process (Koropatkin et al., 2006).

Figure 9: The simplified diagram of the CO₂-concentrating mechanism (CCM) contains three cellular components: component 1 is the HCO₃^- Uptake Systems; component 2 is the CO₂ Uptake Systems; component 3 is the Carboxysomes

cmpABCD, also known as the cmpABCD HCO₃^- transporter system, is an ATP-binding cassette (ABC) transporter located in the cytoplasmic membrane of cyanobacteria to transport HCO₃^- into the cell using energy from ATP hydrolysis (Rottet et al., 2024). This process enables cyanobacteria to concentrate inorganic carbon near the enzyme RuBisCO for efficient photosynthesis. The ABC transporter has a high affinity for HCO₃^-, indicating that the ligand binds strongly to the transporter, making it especially important under low CO₂ conditions. The operon consists of four subunits, as shown in Fig. 10, which will be elaborated on in the next section (Koropatkin et al., 2006).

cmpA (Solute-binding Protein, SBP, also called substrate-binding protein): cmpA is a solute-binding periplasmic protein facing the intermembrane space. cmpA has an active site that captures HCO₃^- and delivers it to the transporter complex cmpB. Structural studies have demonstrated that cmpA has a high affinity and specificity for HCO₃^-(Koropatkin et al., 2006; Q55106 · CMPB_SYNE7, n.d.).

cmpB (Transmembrane Permease): cmpB, a transmembrane protein, is a homodimer that facilitates the transport of HCO₃^- into the cytosol. To move ions against their concentration gradient using ATP energy, cmpB coordinates with cmpC and cmpD, the ATPase subunits, to activate the HCO₃^- transport process. This system is vital for cyanobacteria to sufficiently uptake and concentrate inorganic carbon for photosynthesis under low CO₂ conditions (Omata et al., 1999).

cmpC (ATPase with SBP): cmpC is an ATPase subunit in BCT1. It additionally functions as a substrate-binding protein (SBP). It hydrolyzes ATP through its N-terminal ATP-binding domain to supply the energy needed for HCO₃^- translocation into the cytoplasm. Meanwhile, its C-terminal substrate-binding domain helps the cmpB homodimeric channel optimize HCO₃^- transport (Price et al., 2008; UniProt Consortium, n.d.).

cmpD (ATPase subunit): cmpD, together with cmpC, forms the ATP-hydrolyzing motor that provides energy to the cmpB homodimeric channel, allowing for the active import of HCO₃^- into the cytoplasm in cyanobacteria. This ATP-hydrolyzing motor is pivotal to powering the movement of HCO₃^- against its concentration gradient. This enables the concentration of inorganic carbon within cyanobacteria for photosynthesis under low CO₂ conditions (Omata et al., 1999; Price et al., 2008).

Figure 10: The BCT1 complex contains the cmpA, cmpB, cmpC, and cmpD proteins

Our Final Product: Algae Carbon Sequestration

Taiwan Power Company introduced a model of power plant carbon dioxide in integrated large-scale algae cultivation systems. Research by Taipower in 2015 demonstrated that algal carbon sequestration is more effective than traditional plants and has a smaller environmental impact, allowing carbon dioxide to re-enter the biosphere. Additionally, it may integrate with regional ecosystems, as in integrated multi-trophic aquaculture (IMTA), which would benefit both local life and the ecology. Later on, Taipower went on to research and develop microalgae carbon sequestration technology (The past, present and future of carbon sequestration through algae cultivation, 2022), a foundation for the development of our final product.

Carbon sequestration, the process of capturing and storing atmospheric carbon, is one of the current methods that mitigate global warming. Algae, a diverse group of microscopic aquatic organisms, play a crucial role in carbon sequestration due to their high metabolism rates, enabling them to absorb carbon from the atmosphere effectively. Through their metabolic processes, algae absorb carbon dioxide and incorporate it into their biomass. While algae cultivation is considered a beneficial approach for carbon sequestration, the current rate achieved by algae alone is insufficient to have a significant impact on the global climate (Haoyang, 2017).

Taipower’s project aims to cultivate microalgae in warm water discharge from power plants, thereby reducing CO₂ emissions. Furthermore, it also targeted the advancement of biotechnology products, such as skincare items and nutritional supplements (Chen et al., 2013). Taipower’s mature system introduced a pragmatic approach to algae-based CO₂ capture, recycling of resources, and the circular economy. This biological carbon fixation method offers an effective, sustainable and environmentally friendly alternative to traditional carbon capture techniques (Reduce Carbon While Farming Fish—Taipower’s Shared Ocean Farm Wins Presidential Hackathon Excellent Team Award, n.d.).

Our team is choosing to expand on this algae carbon sequestration model by the Taiwan Power Company because there is already established research regarding this model, and has successfully implemented an algae-based carbon sequestration project in the past decade. Moreover, modeling data reinforces the efficiency of this solution compared to other conventional methods. For our product, we are replacing the algae content with cyanobacteria, aiming to improve the carbon-concentrating mechanism (CCM) in order to increase CO₂ capture. By doing this, we intend to develop a more robust, scalable, and efficient industrial carbon sequestration system that leverages our engineered cyanobacteria’s high carbon-fixation capacity.

To maintain high efficiency, we remain cautious about several environmental factors. For instance, the pH must stay stable to preserve enzyme activity and bicarbonate availability. The temperature, as fluctuations, can affect both cyanobacterial growth and RuBisCO’s oxygenation rate. The composition of input gas, since balancing CO₂ concentration with ambient oxygen levels is critical for maximizing carbon uptake while minimizing photorespiration.

Our Project Design: Optimizing the cmpABCD Operon in the Carbon Concentrating Mechanism (CCM)

Our project addresses the residual gap that even an optimized renewables-plus-CCS portfolio leaves behind by embedding engineered Synechococcus culture in high-surface-area polymer matrices. We have created a modular cyanobacterial carbon dioxide chamber that captures carbon dioxide using sunlight and surplus renewable energy. While cyanobacteria naturally rely on light for photosynthesis, the enclosed chamber requires specific wavelengths of light for activation; therefore, renewable energy allows the system to power the illumination within the chamber, as well as ramp up the operation when renewable energy is in surplus. The modular cyanobacterial carbon dioxide chamber converts directly into carbohydrate-rich biomass and stores the fixed carbon as bioplastics for other applications, thereby removing the long-term liability of deep-geological storage while driving the capture cost toward materials-only levels. The final product could scale into panel-like units that can bolt on industrial facades and surge when renewables overproduce. In doing so, it complements grid-scale renewables and hard-to-abate CCS by providing a biological-powered sink for carbon dioxide to reach net-zero.

To enhance the efficiency of HCO₃^- uptake, our team aims to overexpress the cmpABCD operon under the control of the light-dependent promoter ppsbA1 to ensure that the transporter activity is enhanced. The team engineered two fusion genes, cmpAB and cmpCD, instead of expressing each component separately, to accelerate complex formation. Since the formation of the full cmpABCD transporter typically requires the assembly of four separate subunits, pre-pairing them into two fusion complexes effectively reduces the number of assembly steps, potentially speeding up complex formation and thereby facilitating faster HCO₃^- transport. The resulting polypeptides may promote more rapid and stable assembly of the transporter complex, potentially improving the efficiency of HCO₃^- uptake in the engineered cyanobacterial system.

This theoretically allows us to manipulate the uptake of HCO₃^-, thus increasing carbon fixation efficiency. By optimizing the expression and function of these fusion proteins, we expect to significantly increase inorganic carbon uptake in cyanobacteria, thereby boosting their photosynthetic efficiency and growth under carbon-limited conditions.

References