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Kurt, E.; Qin, J.; Williams, A.; Zhao, Y.; Xie, D. Using CO2 for Biomanufacturing of Fuels and Chemicals. Encyclopedia. Available online: https://encyclopedia.pub/entry/52390 (accessed on 10 May 2024).
Kurt E, Qin J, Williams A, Zhao Y, Xie D. Using CO2 for Biomanufacturing of Fuels and Chemicals. Encyclopedia. Available at: https://encyclopedia.pub/entry/52390. Accessed May 10, 2024.
Kurt, Elif, Jiansong Qin, Alexandria Williams, Youbo Zhao, Dongming Xie. "Using CO2 for Biomanufacturing of Fuels and Chemicals" Encyclopedia, https://encyclopedia.pub/entry/52390 (accessed May 10, 2024).
Kurt, E., Qin, J., Williams, A., Zhao, Y., & Xie, D. (2023, December 05). Using CO2 for Biomanufacturing of Fuels and Chemicals. In Encyclopedia. https://encyclopedia.pub/entry/52390
Kurt, Elif, et al. "Using CO2 for Biomanufacturing of Fuels and Chemicals." Encyclopedia. Web. 05 December, 2023.
Using CO2 for Biomanufacturing of Fuels and Chemicals
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This entry is adapted from the peer-reviewed paper 10.3390/bioengineering10121357

Microbial cell factories offer an eco-friendly alternative for transforming raw materials into commercially valuable products because of their reduced carbon impact compared to conventional industrial procedures. These systems often depend on lignocellulosic feedstocks, mainly pentose and hexose sugars. One major hurdle when utilizing these sugars, especially glucose, is balancing carbon allocation to satisfy energy, cofactor, and other essential component needs for cellular proliferation while maintaining a robust yield. Nearly half or more of this carbon is inevitably lost as CO2 during the biosynthesis of regular metabolic necessities. This loss lowers the production yield and compromises the benefit of reducing greenhouse gas emissions—a fundamental advantage of biomanufacturing.

metabolic engineering CO2 fixation feedstock biomanufacturing electrochemical catalysis microbial electrosynthesis

1. Introduction

Carbon emission to our ecosystem and its accumulation in its highly oxidized state, carbon dioxide (CO2), are the primary contributing factors to global climate change [1]. Since the 1960s, the total CO2 emissions have rapidly increased, with a net annual escalation rate of 2.11% in recent years [2]. The push for carbon neutrality necessitates reimagining our feedstock sources. Over 90% of our chemicals and fuels are manufactured from fossil feedstocks, driving the need to transition toward a more circular industry model. G20 economies have implemented carbon emission taxes ranging from $3 to $60 per ton to incentivize CO2 capture from industrial processes [3]. The cost of carbon capture varies based on the CO2 source [4]. This suggests that, in some countries, obtaining CO2 at zero cost may be possible. Therefore, exploring the potential of capturing and utilizing CO2 is essential to mitigate the global warming challenge.
Photosynthesis is the natural way to capture CO2 from the atmosphere and fix it into sugars or carbohydrates, which can then be used as the feedstocks for microbial cells to produce fuels and chemicals by green plants and algae. Therefore, biomanufacturing is considered more sustainable than chemical manufacturing with petroleum-based feedstocks. However, the production of biomass through the photosynthesis process still suffers the challenge of high-cost processing and low-energy efficiency [5]. While photosynthesis is a marvel of nature, its energy efficiency seldom surpasses 3%, constraining its industrial applicability. Moreover, using agricultural crops to provide feedstocks for biomanufacturing poses a sustainability challenge as it hinders food production and threatens biodiversity when natural areas are used for agricultural purposes.
Sugars such as glucose are the most widely used substrate for biomanufacturing in laboratory and industrial settings for historical and practical reasons. However, employing glucose may repress gene expression and specific biosynthetic pathways for certain biomanufacturing products. In most cases, glucose may also cause several limitations in cell metabolism, resulting in carbon loss as CO2 [6]. This is particularly noticeable when the product of interest requires long synthetic routes from the starting carbon source when it has chemical properties distinct from the substrate or when unfavorable substrates are used, ultimately leading to low product yield [7].
Despite the predominant dependence of current industrial biomanufacturing processes on carbon-intensive carbohydrate substrates, including the C5/C6 sugars such as xylose and glucose derived from cellulosic biomass, it is worth acknowledging that the feedstock and raw materials significantly contribute to the overall cost of biomanufacturing [8]. Reducing the cost can be achieved by using more economical raw materials and designing new microbial cell factories that can efficiently utilize alternative feedstocks. Some microorganisms exhibit the inherent capability or possess the potential to metabolize C1 and C2 substrates [9]. These C1 substrates, comprising CO2, carbon monoxide (CO), methane (CH4), methanol (CH3OH), and formate (CHOO−) [10], and C2 substrates, comprising mainly ethanol and acetate [11], hold the gains of being inexpensive, naturally abundant, and straightforward manufacturing along with their abundant availability as by-products and industrial wastes [9]. Owing to the worldwide attention to continuous conversion of greenhouse gases, specifically CO2 [12] to recover its diminished economic worth, scientists have a special interest in designing innovative CO2 fixation methods with microbial entities, thereby assisting them in the synthesis of crucial substrate precursors (C1 and C2 chemicals) having the inherent capability to serve as biomanufacturing substrate in numerous processes [13][14].
However, the utilization of CO2-derived C1/C2 chemicals for biomanufacturing is challenged by the inefficiency of conversion into desired bioproducts by native microorganisms, resulting in relatively lower productivity, limited energy availability, and deprived carbon yield, as compared with the utilization of C5/C6 sugars [14]. To address the associated challenges, major efforts have been made in the field of synthetic biology and metabolic engineering to evolve both natural microbes [15] and/or heterologous microorganisms by engineering the pathways or enzymes to improve their C1 and C2 substrate-utilizing capabilities [14][16][17][18][19]. Such interventions may range from enhancing native pathways to integrating entirely novel ones crafted from a deep understanding of metabolic networks and enzymology to improve carbon-fixation efficiency [19].
One of the pivotal concerns is the significant carbon loss, especially in the format of CO2 during microbial fermentation [20][21], which comprises the advantageous of using biomanufacturing as one of the major efforts in reducing greenhouse gas emission [22]. Therefore, recycling the exhausted CO2 back to the microbial fermentation process is also critical to the success of biomanufacturing.

2. Current Technologies Using CO2 as a Feedstock for Biomanufacturing of Fuels and Chemicals 

The conversion of CO2 into value-added chemicals using microbes as biocatalysts is an exciting field of research with the potential to revolutionize biomanufacturing processes [23]. For using CO2 as the feedstock for biomanufacturing, both one-step and two-step strategies can be applied. Table 1 summarizes the general strategies for fixation of CO2 for biomanufacturing. The one-step strategy uses the native or engineered pathways to directly fix CO2 and convert it into desired fermentation products, typically with multiple carbons. Since CO2 has the lowest energy format, producing high-value chemicals with a higher energy format requires extra energy; this can be achieved by either plants, algae, or cyanobacteria via a photosynthesis process that uses light as the energy source or other microorganisms with cofeeding higher energy-intensive chemicals such as hydrogen gas. The two-step strategy uses a hybrid electrochemical and biochemical conversion approach to fix CO2 and convert it to the desired fermentation products at higher yield and efficiency, where the first step uses an electrochemical catalysis process to convert CO2 into C1/C2 chemicals, followed by a second fermentation step to further convert C1/C2 chemicals into desired products by native or engineered microorganisms.
Table 1. General strategies for biotechnological fixation of CO2.

Methods

Major Steps and Overall Reaction of CO2 Fixation

One-step/Direct CO2 fixation and conversion

  • Calvin–Benson–Bassham (CBB) Cycle:

 3CO2 + 12 ATP → GAP (→ ½ Glucose)

  • Wood–Ljungdahl Pathway (WLP):

 2CO2 + CoA + 4H+ + 4e− → Acetyl-CoA + 2H2O

  • Reductive Glycine Pathway (rGlyP):

 3CO2 + 3H2 → Pyruvate

  • Reductive Tricarboxylic Acid Cycle (rTCA):

 2CO2 + CoA + 2ATP → Acetyl-CoA

  • 3-Hydroxypropionate (3HP) Bicycle:

 2CO2 + 2ATP → Glyoxylate; CO2 + Glyoxylate + ATP → Pyruvate

  • 3-Hydroxypropionate/4-Hydroxybutyrate (HP/HB) Cycle:

 2CO2 (HCO3−) + CoA + 4ATP → Acetyl-CoA

  • Dicarboxylate/4-Hydroxybutyrate (DC/HB) Cycle:

2CO2 (HCO3−) + CoA + 3ATP → Acetyl-CoA

Two-step CO2 fixation and conversion

Step 1 (electrochemical catalysis):

CO2 + H2O + electricity → C1/C2 chemicals

Step 2 (biomanufacturing):

C1/C2 → biofuels and chemicals

  • CO2 + 2H2O + electricity → CH3OH + 1.5O2

  • CO2 + H2O + electricity → HCOOH + 0.5O2

  • 2CO2 + 3H2O + electricity → C2H5OH + 3O2

  • 2CO2 + 2H2O + electricity → CH3COOH + 2O2

  • CO2 + electricity → CO + 0.5O2

  • CO2 + 2H2O + electricity → CH4 +2O2

  • Direct use of C1/C2:

 C1/C2 → fuels/chemicals + biomass

  • Cofeeding C1/C2 and C5/C6 sugars:

 C1/C2 + C5/C6 sugars → fuels/chemicals + biomass

2.1. One-Step Strategy—Direct Conversion

Internal carbon sequestration has taken many different forms throughout history. Even before the evolution of eukaryotic plants utilizing photosynthesis and light to convert CO2 and energy from light to compose simple sugars, single-celled organisms had already developed mechanisms to capture atmospheric CO2 and transform it into essential compounds for the cell’s development. These primitive mechanisms, especially those in microorganisms like Acetogens and Methanogens, have been shown to be highly efficient in, utilizing unique proteins and metabolic pathways for carbon sequestration [1]. Furthermore, microorganisms, especially microalgae and cyanobacteria, exhibit significant advantages over higher plants in their capacity for CO2 fixation as they can yield higher solar energy retention and the potential for year-round growth compared to their more complex plant counterparts [24]. While microalgae are well-recognized for their CO2 fixation capabilities, bacteria present advantages that cannot be overlooked [25]. Microalgae cultivation can be subject to biocontamination over prolonged use from fungal and bacterial species and often run into issues pertaining to even distribution of sun exposure over larger microalgae ponds due to their preferred growth environments, vastly limiting their ability to be utilized on an industrial scale without major alternations to the water infrastructure the microalgae is grown on. Bacteria and some yeasts, on the other hand, have been widely used in biotechnology industry due to their inherent compatibility to produce chemicals and their rapid growth rates and life cycles. Further, they are more inclined to accept DNA during genetic modification in the form of plasmids and genomic alternations. This ability allows bacteria and yeast to have DNA introduced into their cells of enzymes to complete metabolic pathways previously incompletely represented in the cells and allow production of specialized products, including bioalcohols and essential fatty acids. Through this biotechnological approach, CO2 can be directly converted into value-added products, offering an advantage over traditional methods like catalytic conversion, which demand energy-intensive conditions [23].

2.2. Two-Step Strategy—Fixing CO2 into C1/C2 Chemicals via Electrochemical Catalysis and Converting C1/C2 Chemicals into Bioproducts via Biomanufacturing

The two-step/indirect CO2 fixation and conversion strategy takes the advantages of the current advances from both electrochemical CO2 fixation into C1/C2 chemicals and the synthetic biology to further convert the derived C1/C2 chemicals into the fuels, chemicals, and pharmaceuticals via biomanufacturing process. A primary advantage of these substrates is their non-competitive nature with alimentary resources, which contributes to an economically sustainable framework while diminishing carbon efflux into the biosphere [26]. Nevertheless, it has been widely studied that the C1/C2 substrates can be produced from CO2 via an electrochemical catalysis process [27], which uses renewable electricity from solar, wind, or hydraulic power to capture and fix CO2 into specific C1/C2 products at high yield and selectivity. This two-step CO2 fixation and conversion approach can potentially reduce the dependence on fossil oil-based fuels and chemicals and mitigate the impact of greenhouse gas emissions on the environment [28].

References

  1. Lemaire, O.N.; Jespersen, M.; Wagner, T. CO2-Fixation Strategies in Energy Extremophiles: What Can We Learn from Acetogens? Front. Microbiol. 2020, 11, 486.
  2. Hossain, M.F. Extreme Level of CO2 Accumulation into the Atmosphere Due to the Unequal Global Carbon Emission and Sequestration. Water Air Soil Pollut. 2022, 233, 105.
  3. Bhat, P. Carbon Needs to Cost at Least $100/tonne Now to Reach Net Zero by 2050: Reuters Poll. 2021. Available online: https://www.reuters.com/business/cop/carbon-needs-cost-least-100tonne-now-reach-net-zero-by-2050-2021-10-25/ (accessed on 23 November 2023).
  4. Baylin-Stern, A.; Berghout, N. Is Carbon Capture Too Expensive? 2021. Available online: https://www.iea.org/commentaries/is-carbon-capture-too-expensive (accessed on 23 November 2023).
  5. Claassens, N.J.; Sousa, D.Z.; Dos Santos, V.A.; de Vos, W.M.; van der Oost, J. Harnessing the power of microbial autotrophy. Nat. Rev. Microbiol. 2016, 14, 692–706.
  6. Park, J.O.; Liu, N.; Holinski, K.M.; Emerson, D.F.; Qiao, K.; Woolston, B.M.; Xu, J.; Lazar, Z.; Islam, M.A.; Vidoudez, C. Synergistic substrate cofeeding stimulates reductive metabolism. Nat. Metab. 2019, 1, 643–651.
  7. Liao, J.C.; Mi, L.; Pontrelli, S.; Luo, S. Fuelling the future: Microbial engineering for the production of sustainable biofuels. Nat. Rev. Microbiol. 2016, 14, 288–304.
  8. Xie, D. Continuous biomanufacturing with microbes—Upstream progresses and challenges. Curr. Opin. Biotechnol. 2022, 78, 102793.
  9. Zhang, C.; Ottenheim, C.; Weingarten, M.; Ji, L. Microbial Utilization of Next-Generation Feedstocks for the Biomanufacturing of Value-Added Chemicals and Food Ingredients. Front. Bioeng. Biotechnol. 2022, 10, 874612.
  10. Schrader, J.; Schilling, M.; Holtmann, D.; Sell, D.; Filho, M.V.; Marx, A.; Vorholt, J.A. Methanol-based industrial biotechnology: Current status and future perspectives of methylotrophic bacteria. Trends Biotechnol. 2009, 27, 107–115.
  11. Kiefer, D.; Merkel, M.; Lilge, L.; Henkel, M.; Hausmann, R. From acetate to bio-based products: Underexploited potential for industrial biotechnology. Trends Biotechnol. 2021, 39, 397–411.
  12. Peter, S.C. Reduction of CO2 to Chemicals and Fuels: A Solution to Global Warming and Energy Crisis. ACS Energy Lett. 2018, 3, 1557–1561.
  13. Gomez Vidales, A.; Bruant, G.; Omanovic, S.; Tartakovsky, B. Carbon dioxide conversion to C1-C2 compounds in a microbial electrosynthesis cell with in situ electrodeposition of nickel and iron. Electrochim. Acta 2021, 383, 138349.
  14. Bae, J.; Jin, S.; Kang, S.; Cho, B.-K.; Oh, M.-K. Recent progress in the engineering of C1-utilizing microbes. Curr. Opin. Biotechnol. 2022, 78, 102836.
  15. Iguchi, H.; Yurimoto, H.; Sakai, Y. Interactions of Methylotrophs with Plants and Other Heterotrophic Bacteria. Microorganisms 2015, 3, 137–151.
  16. Chou, A.; Lee, S.H.; Zhu, F.; Clomburg, J.M.; Gonzalez, R. An orthogonal metabolic framework for one-carbon utilization. Nat. Metab. 2021, 3, 1385–1399.
  17. Yu, H.; Liao, J.C. A modified serine cycle in Escherichia coli coverts methanol and CO2 to two-carbon compounds. Nat. Commun. 2018, 9, 3992.
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  21. Xi, Y.-l.; Chen, K.-q.; Li, J.; Fang, X.-j.; Zheng, X.-y.; Sui, S.-S.; Jiang, M.; Wei, P. Optimization of culture conditions in CO2 fixation for succinic acid production using Actinobacillus succinogenes. J. Ind. Microbiol. Biotechnol. 2011, 38, 1605.
  22. Zhang, Q.; Zhang, Q.; Cheng, C.-L.; Nagarajan, D.; Chang, J.-S.; Hu, J.; Lee, D.-J. Carbon capture and utilization of fermentation CO2: Integrated ethanol fermentation and succinic acid production as an efficient platform. Appl. Energy 2017, 206, 364–371.
  23. Salehizadeh, H.; Yan, N.; Farnood, R. Recent advances in microbial CO2 fixation and conversion to value-added products. Chem. Eng. J. 2020, 390, 124584.
  24. Morales, M.; Sánchez, L.; Revah, S. The impact of environmental factors on carbon dioxide fixation by microalgae. FEMS Microbiol. Lett. 2018, 365, fnx262.
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Subjects: Biotechnology & Applied Microbiology
Contributors MDPI registered users' name will be linked to their SciProfiles pages. To register with us, please refer to https://encyclopedia.pub/register :
Elif Kurt
,
Jiansong Qin
,
Alexandria Williams
,
Youbo Zhao
,
Dongming Xie
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Revisions: 2 times (View History)
Update Date: 06 Dec 2023
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