Innovative Approaches: Can Synthetic Biology Combat Climate Change?
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Chapter 1: The Role of Cyanobacteria in Carbon Fixation
Cyanobacteria could be pivotal in lowering atmospheric carbon dioxide levels while enhancing agricultural output. These microorganisms, alongside green algae and diatoms, utilize carbon dioxide for growth, similar to plants.
Update (08 January 2024): This article clarifies that while cyanobacteria are photosynthetic, their processes occur in structures separate from chloroplasts.
The process by which cyanobacteria and other photosynthetic organisms convert carbon dioxide into organic compounds is referred to as carbon fixation. Enhancing this process in food crops could lead to greater yields, thereby potentially mitigating atmospheric carbon dioxide levels.
Section 1.1: Understanding Cyanobacteria and Their Mechanisms
Plants, green algae, and diatoms—classified as eukaryotes—carry out photosynthesis within chloroplasts, which are membrane-enclosed organelles. In contrast, cyanobacteria, being prokaryotes, perform photosynthesis in specialized compartments known as carboxysomes. These protein-bound organelles play a crucial role in carbon fixation.
Despite both chloroplasts and carboxysomes relying on the same enzyme class, RuBisCO (ribulose-1,5-bisphosphate carboxylase/oxygenase), the carbon fixation process is more efficient within carboxysomes.
Carboxysomes enhance carbon fixation efficiency by containing carbonic anhydrase and multiple RuBisCO enzymes, controlling the movement of molecules through their protein shells. Carbonic anhydrase facilitates the conversion of bicarbonate into carbon dioxide, which RuBisCO then utilizes to help synthesize glucose. These organelles possess pores that regulate the entry of bicarbonate and the exit of glucose precursors, effectively minimizing carbon dioxide loss.
Section 1.2: The Engineering Potential of Carboxysomes
The high efficiency of carboxysomes offers significant potential for bioengineering. Researchers aim to enhance carbon fixation in plants or engineer bacteria to optimize carbon capture under specific conditions. To achieve this, understanding the components of carboxysomes, including the shell-forming proteins, is essential.
Notably, different cyanobacteria exhibit variations in carboxysome types. While the protein shell of the α-carboxysome is well understood, that of the β-carboxysome remains less characterized. To create the most effective carboxysome for carbon fixation, scientists must investigate the molecular traits and composition of both types.
By examining the genomes of sequenced cyanobacteria, researchers like Sommer and colleagues identified 227 strains with α-carboxysomes, unveiling two previously unknown shell protein types. Their analysis of co-expressed shell protein genes led to predictions about the minimal requirements for constructing the α-carboxysome shell.
Chapter 2: Advancements in Synthetic Biology
The first video titled "FT009 - Synthetic Biology for Carbon & Climate" explores the potential of synthetic biology in addressing climate change challenges through innovative solutions.
The second video, "Can synthetic biology save the planet?" delves into the transformative possibilities of synthetic biology in combating environmental issues.
Recent structural modeling of carboxysome shells, created solely from three shell proteins, revealed their capabilities. Researchers utilized cryo-electron microscopy (cryo-EM) to visualize these structures, confirming that the pore size allows bicarbonate entry and product exit while preventing substrate access.
Fang and colleagues successfully engineered Escherichia coli to express a dozen genes essential for forming functional α-carboxysomes. Although E. coli do not naturally possess carboxysomes, they were engineered to enhance carbon fixation activity. Furthermore, scientists engineered cyanobacteria to express these genes, increasing both the number of carboxysomes per cell and overall carbon fixation.
In a remarkable experiment, shell proteins from α-carboxysomes were shown to encapsulate RuBisCO from β-carboxysomes, demonstrating the potential to mix and match carboxysome types for optimized carbon fixation. These findings signify a promising advancement for synthetic biologists aiming to utilize these biological systems to tackle carbon emissions and improve crop biomass.
Highlighted Articles
- Sommer et al., "Bioinformatics of α-Carboxysomes: Identification and Evolution," Journal of Experimental Botany 14, 3841–3855 (2017). DOI: 10.1093/jxb/erx115
- Sutter et al., "Structure of a Synthetic α-Carboxysome Shell," Plant Physiology 181, 1050–1058 (2019). DOI: 10.1104/pp.19.00885
- Fang et al., "Engineering Functional Cyanobacterial CO2-fixing Organelles," Frontiers in Plant Science 9, 739 (2018). DOI: 10.3389/fpls.2018.00739