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Bioscience Evidence (online), 2024, Vol. 14 ISSN 1927-6478 https://bioscipublisher.com/index.php/be © 2024 BioSci Publisher, an online publishing platform of Sophia Publishing Group. All Rights Reserved. Sophia Publishing Group (SPG), founded in British Columbia of Canada, is a multilingual publisher Latest Content Process Study on Microbial Fixation of CO2 and Its Conversion into Organic Acids ManmanLi Bioscience Evidence, 2024, Vol. 14, No. 16 Phytoremediation of Soil Contaminated with Lead (Pb) and Zinc (Zn) Using Chromolaena odorata (L.) under Greenhouse Condition O.M. Ajayi, O. Kekere Bioscience Evidence, 2024, Vol. 14, No. 17 Winter Snowpack and Its Role in Water Resource Management and Ecosystem Function Shiying Yu, Jiayao Zhou Bioscience Evidence, 2024, Vol. 14, No. 18 Building Ecosystems: The Transformative Role of Beavers Dan Zhu, Shanshan Yu Bioscience Evidence, 2024, Vol. 14, No. 19 Screening BVOCs in Cypress Cones to Improve Anxiety and Insomnia and Target Prediction Xiangjun Dong Bioscience Evidence, 2024, Vol. 14, No. 20
Bioscience Evidence 2024, Vol.14, No.4, 143-153 http://bioscipublisher.com/index.php/be 143 Research Insight Open Access Process Study on Microbial Fixation of CO2 and Its Conversion into Organic Acids ManmanLi Hainan Institute of Biotechnology, Haikou, 570206, Hainan, China Corresponding author email: manman.li@hibio.org Bioscience Evidence, 2024, Vol.14, No.4 doi: 10.5376/be.2024.14.0016 Received: 17 May, 2024 Accepted: 22 Jun., 2024 Published: 05 Jul., 2024 Copyright © 2024 Li, This is an open access article published under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Preferred citation for this article: Li M.M., 2024, Process study on microbial fixation of CO2 and its conversion into organic acids, Bioscience Evidence, 14(4): 143-153 (doi: 10.5376/be.2024.14.0016) Abstract The study identified several natural and synthetic CO2 fixation pathways, including the Calvin cycle, the Wood-Ljungdahl pathway, and the 3-hydroxypropionate cycle, among others. Key enzymes such as ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) and formate dehydrogenase were found to play crucial roles in these pathways. The research also highlighted the potential of specific bacterial strains, such as Bacillus sp. SS105, in enhancing CO2 sequestration and lipid production for biodiesel applications. Additionally, the study demonstrated that metabolic engineering and optimization of microbial consortia could significantly improve the yields of organic acids like succinic acid and butyric acid. The findings of this study underscore the potential of microbial CO2 fixation as a viable strategy for reducing greenhouse gas emissions and producing valuable organic acids. The identification of efficient microbial pathways and key enzymes, along with advancements in metabolic engineering, paves the way for future applications in sustainable chemical production and biofuel generation. Further research should focus on optimizing these processes to enhance their industrial applicability and economic feasibility. Keywords CO2 fixation; Microbial conversion; Organic acids; Metabolic engineering; RuBisCO; Formate dehydrogenase; Bacillus sp. SS105; Biodiesel; Succinic acid; Butyric acid 1 Introduction The continuous rise in global CO2 emissions has significantly contributed to climate change, leading to severe environmental consequences such as global warming, ocean acidification, and extreme weather events. The increasing concentration of CO2 in the atmosphere is primarily due to human activities, including the burning of fossil fuels, deforestation, and industrial processes (Salehizadeh et al., 2020; Wang et al., 2023). These emissions have resulted in unprecedented levels of greenhouse gases, which trap heat in the atmosphere and disrupt the natural balance of the Earth's climate system (Salehizadeh et al., 2020). Carbon fixation is a crucial process in mitigating the adverse effects of greenhouse gases. By converting CO2 into organic compounds, carbon fixation helps reduce the overall concentration of CO2 in the atmosphere. This process not only addresses the environmental impact of CO2 emissions but also provides a sustainable approach to producing valuable chemicals and fuels. Microbial CO2 fixation, in particular, has gained attention due to its potential to efficiently convert CO2 into various organic acids and other value-added products (Salehizadeh et al., 2020; Chen et al., 2023; Wang et al., 2023). Microbial CO2 fixation involves the use of microorganisms to convert CO2 into organic compounds through various metabolic pathways. Several natural and synthetic pathways have been identified, including the Calvin cycle, the Wood-Ljungdahl pathway, and the 3-hydroxypropionate/4-hydroxybutyrate cycle. These pathways enable microorganisms to assimilate CO2 as a carbon source and produce a range of metabolites, such as organic acids, alcohols, and bioplastics (Salehizadeh et al., 2020; Zhang et al., 2020; Wang et al., 2023). Advances in genetic and metabolic engineering have further enhanced the efficiency and versatility of microbial CO2 fixation processes (Salehizadeh et al., 2020; Zhang et al., 2020; Chen et al., 2023). The conversion of CO2 into organic acids is particularly relevant due to the high demand for these compounds in various industrial applications. Organic acids, such as acetic acid, succinic acid, and butyric acid, serve as key intermediates in the production of bioplastics, pharmaceuticals, and biofuels (Liu et al., 2018; Mateos et al., 2019;
Bioscience Evidence 2024, Vol.14, No.4, 143-153 http://bioscipublisher.com/index.php/be 144 Chen et al., 2023). Microbial electrosynthesis (MES) systems have shown promise in enhancing the conversion efficiency of CO2 to organic acids by utilizing bioelectrochemical processes. These systems leverage the metabolic capabilities of microorganisms to produce organic acids with high selectivity and yield (Song et al., 2011; Liu et al., 2018; Mateos et al., 2019; Wang, 2024). The primary objective of this study is to investigate the microbial fixation of CO2 and its subsequent conversion into organic acids. This research aims to explore the various microbial pathways involved in CO2 fixation, evaluate the efficiency of different microbial systems, and identify potential strategies to enhance the production of organic acids. By understanding and optimizing these processes, this study hopes to contribute to the development of sustainable and economically viable methods for reducing CO2 emissions and producing valuable biochemicals. 2 Mechanisms of Microbial CO2 Fixation 2.1 Overview of CO2 fixation pathways Microbial CO2 fixation involves several distinct biochemical pathways that convert atmospheric CO2 into organic compounds. The most well-known pathway is the Calvin-Bassham-Benson (CBB) cycle, which is prevalent in many autotrophic organisms and involves the enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase (RubisCO) (Dangel and Tabita, 2015; Xiao et al., 2020; Asplund-Samuelsson and Hudson, 2021). Other pathways include the reductive citric acid cycle, the reductive acetyl-CoA pathway (Wood-Ljungdahl pathway), the 3-hydroxypropionate bicycle, the dicarboxylate/4-hydroxybutyrate cycle, and the 3-hydroxypropionate/4-hydroxybutyrate cycle (Sánchez-Andrea et al., 2020; Xiao et al., 2020; Chen et al., 2021). Recently, a seventh pathway, the reductive glycine pathway, has been identified in Desulfovibrio desulfuricans, which is highly ATP-efficient (Sánchez-Andrea et al., 2020). 2.2 Key microorganisms involved Various microorganisms are involved in CO2 fixation, including both photoautotrophic and chemoautotrophic bacteria. Cyanobacteria are well-known for their role in the CBB cycle, while other bacteria such as Clostridium ljungdahlii utilize the Wood-Ljungdahl pathway (Schuchmann and Müller, 2014; Zhang et al., 2020). Sulfate-reducing bacteria like Desulfovibrio desulfuricans employ the reductive glycine pathway (Sánchez-Andrea et al., 2020). Additionally, heterotrophic microorganisms have been engineered to enhance CO2 fixation capabilities, leveraging their fast growth and ease of genetic modification (Hu et al., 2022). 2.3 Genetic and enzymatic basis The genetic basis for CO2 fixation involves a variety of genes encoding enzymes that catalyze the key steps in these pathways. For instance, the cbbL genes encode the large subunit of RubisCO in the CBB cycle, which is a critical enzyme for CO2 fixation (Xiao et al., 2020; Asplund-Samuelsson and Hudson, 2021). Other important enzymes include formate dehydrogenase in the reductive glycine pathway and acetyl-CoA synthase in the Wood-Ljungdahl pathway (Sánchez-Andrea et al., 2020; Zhang et al., 2020). Regulatory proteins such as CbbR play a crucial role in controlling the expression of these genes, ensuring the efficient operation of the CO2 fixation pathways (Dangel and Tabita, 2015). 2.4 Challenges in CO2 fixation Despite the potential of microbial CO2 fixation, several challenges remain. One major issue is the efficiency of CO2 fixation, which can be limited by the availability of energy and reducing equivalents (Gong et al., 2019; Hu et al., 2022). Additionally, the integration of CO2 fixation pathways into heterotrophic microorganisms requires careful optimization to balance metabolic fluxes and avoid the accumulation of toxic intermediates (Hu et al., 2022). Environmental factors such as the presence of pollutants can also impact the efficiency of microbial CO2 fixation (Chen et al., 2021). Addressing these challenges through metabolic engineering and synthetic biology approaches is crucial for enhancing the viability of microbial CO2 fixation as a sustainable solution for carbon capture and conversion (Gong et al., 2019; Salehizadeh et al., 2020; Hu et al., 2022).
Bioscience Evidence 2024, Vol.14, No.4, 143-153 http://bioscipublisher.com/index.php/be 145 3 Conversion of Fixed CO2 into Organic Acids 3.1 Pathways for organic acid production Microbial fixation of CO2 and its subsequent conversion into organic acids involves several metabolic pathways. Key pathways include the Calvin cycle, the reduced tricarboxylic acid (rTCA) cycle, the Wood-Ljungdahl (WL) pathway, the 3-hydroxypropionate/4-hydroxybutyrate (HP/HB) cycle, the dicarboxylate/4-hydroxybutyrate (DC/HB) cycle, and the 3-hydroxypropionate (3HP) cycle. Additionally, synthetic pathways such as the CETCH cycle, the MOG pathway, the acetyl-CoA bicycle, and the POAP cycle have been designed to enhance CO2 fixation and conversion efficiency (Salehizadeh et al., 2020; Wang et al., 2023). Acetic Acid: Acetic acid production is prominently facilitated by acetogenic bacteria such as Clostridium scatologenes and Moorella thermoacetica through the Wood-Ljungdahl pathway. These bacteria can convert CO2 into acetic acid under anaerobic conditions, often using H2 as an electron donor (Song et al., 2011; Liu et al., 2018). Microbial electrosynthesis (MES) systems have also been shown to enhance acetic acid production by improving CO2 availability and electron transfer efficiency (Mateos et al., 2019) (Figure 1). Lactic Acid: Lactic acid production from CO2 is less common but can be achieved through engineered microbial strains. Genetic modifications in lactic acid bacteria can enable the utilization of CO2 as a carbon source, although this area requires further research and development (Salehizadeh et al., 2020). Succinic Acid: Succinic acid is another valuable product derived from CO2 fixation. The production of succinic acid involves the reductive branch of the TCA cycle. Enhancing CO2 utilization efficiency through genetic and metabolic engineering has been a focus to improve succinic acid yields. Strategies include optimizing CO2 supply methods and employing advanced biotechnological approaches such as micro-nano bubbles and CO2 adsorption materials (Liebal et al., 2018; Chen et al., 2023). 3.2 Microbial engineering for enhanced production Genetic and metabolic engineering play crucial roles in enhancing the microbial conversion of CO2 into organic acids. Key strategies include: Enzyme Optimization: Improving the efficiency of carbon fixation enzymes such as ribulose-1,5-diphosphate carboxylase/oxygenase (RuBisCO), pyruvate carboxylase, and formate dehydrogenase (FDH) can significantly boost CO2 fixation rates. For instance, the regulation of FDH1 by lysine acetylation and transcriptional factors in Clostridium ljungdahlii has been shown to enhance CO2 metabolism (Zhang et al., 2020). Figure 1 Image and diagram of reactor setup (Adopted from Mateos et al., 2019) Image caption: CE: counter electrode; RE: reference electrode; WE: working electrode (Adopted from Mateos et al., 2019)
Bioscience Evidence 2024, Vol.14, No.4, 143-153 http://bioscipublisher.com/index.php/be 146 Pathway Engineering: Introducing and optimizing synthetic pathways like the CETCH cycle and the MOG pathway in model organisms such as Escherichia coli and yeast can lead to higher yields of target organic acids. These pathways are designed to be more efficient than natural CO2 fixation routes (Wang et al., 2023). Electrochemical Systems: Utilizing microbial electrosynthesis (MES) systems can improve the conversion efficiency of CO2 to organic acids. By optimizing the bioelectrochemical conditions, such as cathodic potential and electron transfer mechanisms, the production of acetic acid and other organic acids can be significantly enhanced (Liu et al., 2018; Mateos et al., 2019) (Table 1). Mixed-Culture Biocathodes: Employing mixed microbial cultures in bioelectrochemical systems can stabilize reactor performance and enhance CO2 reduction. For example, a mixed-culture biocathode containing Sporomusa and Clostridium species has been shown to effectively convert CO2 to acetate (Mateos et al., 2019). By integrating these approaches, the microbial fixation of CO2 and its conversion into valuable organic acids can be optimized, contributing to sustainable and economically viable bioprocesses. 4 Process Optimization for Industrial Applications 4.1 Fermentation process design Designing an effective microbial fermentation process for CO2 fixation and organic acid production involves optimizing several key parameters. These include substrate utilization, microbial community enrichment, and operational parameters such as pH, temperature, and partial pressure of gases. For instance, dark fermentation processes have shown that optimizing these parameters can significantly enhance biohydrogen yield and the production of valuable by-products like volatile fatty acids (Ghimire et al., 2015). Additionally, maintaining a sufficient CO2 transfer rate and optimizing pH levels can improve succinate yield in bioreactors (Wu et al., 2012). 4.2 Bioreactor technologies Various bioreactor types and configurations have been developed to optimize microbial CO2 fixation. Continuous stirred-tank reactors (CSTR) and immobilized cell reactors are commonly used, with the latter showing advantages in mass transfer and cell density (Klasson et al., 1991). Hollow fiber membrane bioreactors (L/G MBR) have also been developed to combine biohydrogen production, in situ liquid-gas separation, and bacteria retention, which simplifies the fermentation process and enhances hydrogen yield (Renaudie et al., 2021). Additionally, bioreactors equipped with self-inducing agitators have been shown to reduce CO2 waste and improve succinate production (Wu et al., 2012). 4.3 Scale-up challenges Scaling up microbial CO2 fixation processes from lab to industrial scale presents several challenges. One major issue is the mass transfer limitation due to low gas solubilities, which can hinder the efficiency of the process (Klasson et al., 1991). Additionally, maintaining consistent microbial activity and product yield at larger scales can be difficult. For example, the performance of syngas fermentation processes can be significantly affected by mass transfer rates and gas flow profiles, which need to be carefully managed in large-scale bioreactors (Benalcázar et al., 2020). Furthermore, the integration of gasification and fermentation processes remains an underdeveloped area that requires further research to achieve technological breakthroughs (Pacheco et al., 2023). Table 1 Results of hydrogen autotrophic fermentation and microbial electrosynthesis experiments (Adopted from Liu et al., 2018) OD600,max Formate (g/L, max) Acetate (g/L,max) Butyrate (g/L,max) Ethanol (g/L, max) Rate of acetate (g/L/d) H2 (%) 80%H2–10%CO2 0.120 0.023 1.250 0.320 0.192 0.170 80 10%H2–10%CO2–80%N2 0.110 0.008 0.362 0.145 0.083 0.050 10 −0.6V 0.052 – 0.030 0.010 0 0.001 0 −0.8V 0.055 – 0.095 0.051 0.010 0.012 4.7972 −1.05V 0.059 – 0.301 0.059 0.013 0.041 9.7412 −1.2V 0.063 – 0.440 0.085 0.015 0.060 13.1777
Bioscience Evidence 2024, Vol.14, No.4, 143-153 http://bioscipublisher.com/index.php/be 147 4.4 Economic and environmental implications The economic viability of microbial CO2 fixation processes depends on several factors, including the cost of substrates, bioreactor design, and operational efficiency. Utilizing by-products from fermentation processes, such as volatile fatty acids, can enhance the economic feasibility by providing additional revenue streams (Ghimire et al., 2015). Moreover, integrated systems that combine CO2 fixation with other fermentation processes, such as ethanol production, can reduce costs by utilizing CO2 produced during ethanol fermentation (Wu et al., 2012; Zhang et al., 2017). Converting CO2 into organic acids offers significant environmental benefits by reducing greenhouse gas emissions and producing valuable bio-based chemicals. For instance, the production of succinic acid from CO2 can replace petroleum-based production methods, contributing to sustainability and reducing the carbon footprint (Ferone et al., 2019). Additionally, integrated fermentation processes that utilize CO2 from ethanol production can further enhance environmental benefits by minimizing CO2 emissions. The use of non-photosynthetic microorganisms for CO2 fixation has also been shown to be more efficient than microalgae-based biofuels, providing a more effective pathway for carbon capture and utilization (Zhang et al., 2017). 5 Case Studies 5.1 Case study 1: engineering E. coli for enhanced succinic acid production from CO2 The engineering of Escherichia coli for enhanced succinic acid production from CO2 involves several genetic modifications and process optimizations. One approach includes the heterologous expression of genes from the reductive tricarboxylic acid (rTCA) cycle. Specifically, ten genes encoding key rTCA cycle enzymes such as α-ketoglutarate:ferredoxin oxidoreductase, ATP-dependent citrate lyase, and fumarate reductase/succinate dehydrogenase were cloned into E. coli. This transgenic strain demonstrated enhanced growth and the ability to assimilate external inorganic carbon with a gaseous CO2 supply (Lo et al., 2021). Additionally, metabolic engineering strategies have been employed to improve CO2 utilization efficiency, including the use of micro-nano bubbles and CO2 adsorption materials (Chen et al., 2023). Directed evolution of enzymes like propionyl-CoA carboxylase has also been applied to enhance the catalytic efficiency of CO2 fixation pathways (Liu et al., 2020). The genetically modified E. coli strains showed significant improvements in CO2 assimilation and succinic acid production. For instance, the transgenic strain with rTCA cycle genes exhibited CO2-enhanced growth and upregulation of genes involved in chemotaxis, flagellar assembly, and acid-resistance under anaerobic conditions (Lo et al., 2021) (Figure 2). Computational analyses have indicated that with optimized parameters, microbial succinate production processes could reach economically viable levels, making them promising alternatives to traditional sugar-based fermentations (Liebal et al., 2018). These advancements suggest that engineered E. coli could play a crucial role in sustainable industrial applications, potentially reducing greenhouse gas emissions and providing a cost-effective method for producing bio-based chemicals. 5.2 Case study 2: cyanobacteria as a platform for lactic acid production Cyanobacteria have been explored as a platform for lactic acid production due to their ability to fix CO2 and convert it into valuable chemicals. Strategies to enhance lactic acid yield include metabolic engineering to increase the flux through the reductive TCA branch and the use of nutritional supplements like corn-steep liquor (CSL) to boost production. For example, the recombinant strain PCCK of Synechocystis sp. PCC6803, which expresses foreign ATP-forming phosphoenolpyruvate carboxykinase (PEPck) along with overexpressed intrinsic phosphoenolpyruvate carboxylase (Ppc), showed increased production of C4 dicarboxylic acids, which can be further converted into lactic acid (Hidese et al., 2022). The economic viability and scalability of using cyanobacteria for lactic acid production depend on several factors, including the efficiency of CO2 fixation and the overall production costs. High-density cultivation and the use of non-sterile CSL have been shown to significantly enhance the production of malate, fumarate, and succinate, which are precursors for lactic acid production (Hidese et al., 2022). These findings suggest that with further optimization, cyanobacteria could provide a scalable and economically viable platform for lactic acid production, contributing to a sustainable bioeconomy.
Bioscience Evidence 2024, Vol.14, No.4, 143-153 http://bioscipublisher.com/index.php/be 148 Figure 2 Designed genetic pathway and growth of transgenic E. coli strains with different inorganic carbon sources (Adopted from Lo et al., 2021) Image caption: (a) Pathway map of CO2 assimilation enzymes related to this study. The heterologously expressed enzymes are marked in red. AclBA, ATP-dependent citrate lyase; KorAB, α-ketoglutarate:ferredoxin oxidoreductase; FrdABC/SdhCAB, fumarate reductase. Blue arrows represent TCA cycle activities contributed by E. coli genes; arrowheads indicate oxidative (clockwise) or reductive (counter-clockwise) activities; blue/red activity lines are oxidative direction only for E. coli enzymes or reversible for cloned C. tepidumenzymes. (b) DNA cassettes used to construct the expression plasmid pGETS-KAFS, which encodes the korAB, aclBA, frdABC, and sdhCAB genes from C. tepidum. (c) Anaerobic growth curves of transgenic E. coli strains with CO2 or bicarbonate present in glucose culture medium. Data are expressed as the means ± standard deviations, n = 3 independent biological samples (Adopted from Lo et al., 2021)
Bioscience Evidence 2024, Vol.14, No.4, 143-153 http://bioscipublisher.com/index.php/be 149 5.3 Case study 3: methanogens for acetic acid production Methanogens have been investigated for their potential to produce acetic acid from CO2 through various metabolic pathways. The exploration of these pathways involves understanding the enzymatic mechanisms and optimizing reactor designs to enhance CO2 fixation and conversion efficiency. For instance, the use of bioreactors with optimized gas and photon transfer rates has been shown to improve the performance of microbial CO2 assimilation processes (Liebal et al., 2018). The sustainability and cost-effectiveness of using methanogens for acetic acid production are evaluated based on their ability to fix CO2 and the overall production costs (Figure 3). Early assessments using stoichiometric metabolic modeling have indicated that while current microbial processes may not yet be competitive with traditional methods, optimized parameters could make them economically interesting alternatives (Liebal et al., 2018). The development of high-activity enzymes and efficient bioreactor designs are crucial for achieving sustainable and cost-effective acetic acid production from CO2. By leveraging genetic modifications, process optimizations, and innovative reactor designs, these case studies highlight the potential of microbial CO2 fixation and conversion into valuable organic acids, paving the way for sustainable industrial applications. Figure 3 Pathways of carbon fixation to succinate investigated in this study for their economic potential (Adopted from Liebal et al., 2018) Image caption: The reductive pentose phosphate pathway (green), DHAP pathway of methylotrophic yeasts (blue), reductive acetyl-CoA pathway (C. ljungdahlii, yellow), glyoxylate shunt (E. coli, orange), and CETCH pathway (purple). Ac, acetate; AcCoA, acetyl-CoA; AcrCoA, acrylyl-CoA; CH3-THF, methyltetrahydrofolate; CroCoA, crotonyl-CoA; DHAP, dihydroxyacetone phosphate; EthMalCoA, ethylmalonyl-CoA; E4P, erythrose-4-phosphate; Fum, fumarate; F6P, fructose-6-phosphate; GAP, glyceraldehyde-3; Glyox, glyoxylate; Icit, isocitrate; Mal, malate; MeMalCoA, methylmalyl-CoA; MeManlCoA, methylmalonyl-CoA; OAA, oxaloacetate; OGA, 2-oxoglutarate; PEP, phosphoenol pyruvate; PropCoA, propionyl-CoA; Pyr, Pyruvate; RuBP, ribulose-bisphosphate; Ru5P, ribulose-5-phosphat; R5P, ribose-5-phosphate; Suc, succinate; SucCoA, succinyl-CoA; S7P, sedoheptulose-7-phosphate; X5P, xylulose-5-phosphate; 3PG, 3-phosphoglycerate; 4HBut, 4-hydroxyburyrate (Adopted from Liebal et al., 2018)
Bioscience Evidence 2024, Vol.14, No.4, 143-153 http://bioscipublisher.com/index.php/be 150 6 Applications and Future Prospects 6.1 Industrial applications Microbially produced organic acids have a wide range of applications across various industries, including pharmaceuticals, food, and biofuels. In the pharmaceutical industry, organic acids such as lactic acid and itaconic acid are used as building blocks for the synthesis of various drugs and medical products (Baumschabl et al., 2022). The food industry utilizes organic acids like citric acid and fumaric acid as preservatives, flavor enhancers, and acidulants, contributing to the taste and shelf-life of food products (Lorenzo et al., 2022). Additionally, the biofuel industry benefits from organic acids such as succinic acid, which can be converted into bio-based chemicals and fuels, providing a sustainable alternative to fossil fuels (Liebal et al., 2018; Reddy et al., 2020). The microbial production of these acids offers a more sustainable and environmentally friendly approach compared to traditional chemical synthesis, which relies on depletable petroleum resources and harsh reaction conditions (Li et al., 2021). 6.2 Integration with carbon capture technologies The integration of microbial CO2 fixation with carbon capture and storage (CCS) systems presents a promising approach to mitigate greenhouse gas emissions while producing valuable organic acids. Microbial CO2 fixation pathways, such as the Calvin cycle and the Wood-Ljungdahl pathway, can be harnessed to convert captured CO2 into organic acids, thus providing a dual benefit of carbon sequestration and production of industrially relevant chemicals (Salehizadeh et al., 2020; Wang et al., 2023). This approach can be further enhanced by coupling microbial and electrochemical methods, which have shown potential in producing carboxylic acids and alcohols from CO2 using reducing power provided by electrodes (Vassilev et al., 2018). By integrating these microbial processes with existing CCS infrastructure, it is possible to create a more sustainable and economically viable system for reducing atmospheric CO2 levels while generating valuable products (Chen et al., 2023). 6.3 Future research directions Future research should focus on several key areas to improve the efficiency of microbial CO2 fixation and expand the range of products that can be synthesized. One critical area is the enhancement of carbon fixation enzymes and metabolic pathways to increase the conversion rates and yields of organic acids (Salehizadeh et al., 2020; Wang et al., 2023). Genetic and metabolic engineering strategies can be employed to optimize microbial strains for higher productivity and broader substrate utilization (Reddy et al., 2020; Li et al., 2021). Additionally, exploring the potential of mixed microbial consortia and co-culturing schemes can lead to the discovery of new microbial interactions and pathways that enhance the production of target compounds (Konstantinidi et al., 2023). Another important research direction is the development of advanced bioreactor designs and process optimization techniques to improve the scalability and economic feasibility of microbial CO2 fixation processes (Liebal et al., 2018; Lin, 2024). By addressing these challenges, it will be possible to create more efficient and versatile microbial cell factories capable of producing a wide range of valuable organic acids from CO2. 7 Concluding Remarks Microbial CO2 fixation and its conversion into organic acids have emerged as promising strategies to mitigate greenhouse gas emissions and produce valuable biochemicals. Various natural and synthetic pathways have been identified for microbial CO2 fixation, including the Calvin cycle, the Wood-Ljungdahl pathway, and the 3-hydroxypropionate/4-hydroxybutyrate cycle, among others. Key enzymes such as ribulose-1,5-bisphosphate carboxylase/oxygenase (RubisCO) and formate dehydrogenase play crucial roles in these processes. Microbial electrosynthesis (MES) has also shown potential in converting CO2 into organic acids like acetic and butyric acid, with Clostridium scatologenes and other acetogenic bacteria demonstrating significant efficiency in these conversions. Genetic and metabolic engineering have further enhanced the efficiency of these microbial processes, making them viable for industrial applications. The long-term impact of microbial CO2 fixation technologies could be substantial in reducing global CO2 levels. By leveraging the natural ability of microorganisms to assimilate CO2 and convert it into valuable organic compounds, these technologies offer a sustainable and eco-friendly alternative to traditional CO2 capture methods, which are often cost-inefficient and environmentally hazardous. The integration of microbial CO2 fixation with
Bioscience Evidence 2024, Vol.14, No.4, 143-153 http://bioscipublisher.com/index.php/be 151 bioelectrochemical systems (BESs) and MES can further enhance the efficiency and scalability of these processes, potentially leading to significant reductions in atmospheric CO2 levels. Additionally, the development of robust microbial strains through genetic and metabolic engineering could optimize CO2 fixation rates and product yields, making these technologies economically viable for large-scale deployment. The future of microbial processes in sustainable industrial practices looks promising, with microbial CO2 fixation and conversion technologies poised to play a critical role in addressing climate change and promoting green manufacturing. The continuous advancements in understanding microbial metabolic pathways, coupled with innovations in genetic engineering and bioelectrochemical systems, are likely to drive the development of more efficient and cost-effective CO2 fixation processes. As these technologies mature, they could be integrated into various industrial applications, from biofuel production to the synthesis of high-value chemicals, thereby contributing to a circular carbon economy and reducing our reliance on fossil fuels. The collaborative efforts of researchers, industry stakeholders, and policymakers will be essential in realizing the full potential of microbial CO2 fixation technologies and ensuring their successful implementation in sustainable industrial practices. Acknowledgments Sincere thanks to the peer reviewers for their detailed reviews and valuable guidance on this manuscript. Conflict of Interest Disclosure The author affirms that this research was conducted without any commercial or financial relationships that could be construed as a potential conflict of interest. References Asplund-Samuelsson J., and Hudson E., 2021, Wide range of metabolic adaptations to the acquisition of the Calvin cycle revealed by comparison of microbial genomes, PLoS Computational Biology, 17(2): e1008742. https://doi.org/10.1371/journal.pcbi.1008742 Baumschabl M., Ata Ö., Mitic B., Lutz L., Gassler T., Troyer C., Hann S., and Mattanovich D., 2022, Conversion of CO2 into organic acids by engineered autotrophic yeast, Proceedings of the National Academy of Sciences of the United States of America, 119(47): e2211827119. https://doi.org/10.1073/pnas.2211827119 Benalcázar E., Noorman H., Filho R., and Posada J., 2020, Modeling ethanol production through gas fermentation: a biothermodynamics and mass transfer-based hybrid model for microbial growth in a large-scale bubble column bioreactor, Biotechnology for Biofuels, 13: 1-19. https://doi.org/10.1186/s13068-020-01695-y Chen K., He R., Wang L., Liu L., Huang X., Ping J., Huang C., Wang X., and Liu Y., 2021, The dominant microbial metabolic pathway of the petroleum hydrocarbons in the soil of shale gas field: Carbon fixation instead of CO2 emissions, The Science of the total environment, 807: 151074. https://doi.org/10.1016/j.scitotenv.2021.151074 Chen X., Wu H., Chen Y., Liao J., Zhang W., and Jiang M., 2023, Recent advancements and strategies of improving CO2 utilization efficiency in bio-succinic acid production, Fermentation, 9(11): 967. https://doi.org/10.3390/fermentation9110967 Dangel A., and Tabita F., 2015, CbbR, the master regulator for microbial carbon dioxide fixation, Journal of Bacteriology, 197: 3488-3498. https://doi.org/10.1128/JB.00442-15 Ferone M., Raganati F., Olivieri G., and Marzocchella A., 2019, Bioreactors for succinic acid production processes, Critical Reviews in Biotechnology, 39: 571-586. https://doi.org/10.1080/07388551.2019.1592105 Ghimire A., Frunzo L., Pirozzi F., Trably E., Escudié R., Lens P., and Esposito G., 2015, A review on dark fermentative biohydrogen production from organic biomass: Process parameters and use of by-products, Applied Energy, 144: 73-95. https://doi.org/10.1016/j.apenergy.2015.01.045 Gong F., Zhu H., Zhou J., Zhao T., Xiao L., Zhang Y., and Li Y., 2019, Enhanced biological fixation of CO2 using microorganisms, In: Aresta M., Karimi I., Kawi S. (eds) An Economy Based on Carbon Dioxide and Water. Springer, Cham, pp.359-378. https://doi.org/10.1007/978-3-030-15868-2_10 Hidese R., Matsuda M., Kajikawa M., Osanai T., Kondo A., and Hasunuma T., 2022, Metabolic and microbial community engineering for four-carbon dicarboxylic acid production from CO2-derived glycogen in the Cyanobacterium Synechocystis sp. PCC6803, ACS Synthetic Biology, 11(12): 4054-4064. https://doi.org/10.1021/acssynbio.2c00379 Hu G., Song W., Gao C., Guo L., Chen X., and Liu L., 2022, Advances in synthetic biology of CO2 fixation by heterotrophic microorganisms, Sheng wu gong cheng xue bao = Chinese journal of biotechnology, 38(4): 1339-1350.
Bioscience Evidence 2024, Vol.14, No.4, 143-153 http://bioscipublisher.com/index.php/be 152 Klasson K., Ackerson M., Clausen E., and Gaddy J., 1991, Bioreactor design for synthesis gas fermentations, Fuel, 70: 605-614. https://doi.org/10.1016/0016-2361(91)90174-9 Konstantinidi S., Skiadas I., and Gavala H., 2023, Microbial enrichment techniques on syngas and CO2 targeting production of higher acids and alcohols, Molecules, 28(6): 2562. https://doi.org/10.3390/molecules28062562 Li Y., Yang S., Ma D., Song W., Gao C., Liu L., and Chen X., 2021, Microbial engineering for the production of C2-C6 organic acids, Natural Product Reports, 38(8): 1518-1546. https://doi.org/10.1039/D0NP00062K Liebal U., Blank L., and Ebert B., 2018, CO2 to succinic acid - Estimating the potential of biocatalytic routes, Metabolic Engineering Communications, 7: e00075. https://doi.org/10.1016/j.mec.2018.e00075 Lin J., 2024, Sustainable Development strategy of bioenergy and global energy transformation, Journal of Energy Bioscience, 15(1): 10-19. Liu H., Song T., Fei K., Wang H., and Xie J., 2018, Microbial electrosynthesis of organic chemicals from CO2 by Clostridium scatologenes ATCC 25775T, Bioresources and Bioprocessing, 5: 1-10. https://doi.org/10.1186/s40643-018-0195-7 Liu X., Feng X., Ding Y., Gao W., Xian M., Wang J., and Zhao G., 2020, Characterization and directed evolution of propionyl-CoA carboxylase and its application in succinate biosynthetic pathway with two CO2 fixation reactions, Metabolic Engineering, 62: 42-50. https://doi.org/10.1016/j.ymben.2020.08.012 Lo S., Chiang E., Yang Y., Li S., Peng J., Tsai S., Wu D., Yu C., Huang C., Su T., Tsuge K., and Huang C., 2021, Growth enhancement facilitated by gaseous CO2 through heterologous expression of reductive tricarboxylic acid cycle genes in Escherichia coli, Fermentation, 7(2): 98. https://doi.org/10.3390/fermentation7020098 Lorenzo R., Serra I., Porro D., and Branduardi P., 2022, State of the art on the microbial production of industrially relevant organic acids, Catalysts, 12(2): 234. https://doi.org/10.3390/catal12020234 Mateos R., Sotres A., Alonso R., Morán A., and Escapa A., 2019, Enhanced CO2 conversion to acetate through microbial electrosynthesis (MES) by continuous headspace gas recirculation, Energies, 12(17): 3297. https://doi.org/10.3390/en12173297 Pacheco M., Moura P., and Silva C., 2023, A systematic review of syngas bioconversion to value-added products from 2012 to 2022, Energies, 16(7): 3241. https://doi.org/10.3390/en16073241 Reddy M., Kumar G., Mohanakrishna G., Shobana S., and Al-Raoush R., 2020, Review on the production of medium and small chain fatty acids through waste valorization and CO2 fixation, Bioresource Technology, 309: 123400. https://doi.org/10.1016/j.biortech.2020.123400 Renaudie M., Clion V., Dumas C., Vuilleumier S., and Ernst B., 2021, Intensification and optimization of continuous hydrogen production by dark fermentation in a new design liquid/gas hollow fiber membrane bioreactor, Chemical Engineering Journal, 416: 129068. https://doi.org/10.1016/j.cej.2021.129068 Salehizadeh H., Yan N., and Farnood R., 2020, Recent advances in microbial CO2 fixation and conversion to value-added products, Chemical Engineering Journal, 390: 124584. https://doi.org/10.1016/j.cej.2020.124584 Sánchez-Andrea I., Guedes I., Hornung B., Boeren S., Lawson C., Sousa D., Bar-Even A., Claassens N., and Stams A., 2020, The reductive glycine pathway allows autotrophic growth of Desulfovibrio desulfuricans, Nature Communications, 11(1): 1-12. https://doi.org/10.1038/s41467-020-18906-7 Schuchmann K., and Müller V., 2014, Autotrophy at the thermodynamic limit of life: a model for energy conservation in acetogenic bacteria, Nature Reviews Microbiology, 12: 809-821. https://doi.org/10.1038/nrmicro3365 Song J., Kim Y., Lim M., Lee H., Lee J., and Shin W., 2011, Microbes as electrochemical CO2 conversion catalysts, ChemSusChem, 4(5): 587-590. https://doi.org/10.1002/cssc.201100107 Vassilev I., Hernandez P., Batlle-Vilanova P., Freguia S., Krömer J., Keller J., Ledezma P., and Virdis B., 2018, Microbial electrosynthesis of isobutyric, butyric, caproic acids, and corresponding alcohols from carbon dioxide, ACS Sustainable Chemistry and Engineering, 6(7): 8485-8493. https://doi.org/10.1021/acssuschemeng.8b00739 Wang M.H., 2024, Study on electron transfer mechanisms of electroactive bacteria in microbial fuel cells, Journal of Energy Bioscience, 15(2): 87-97. https://doi.org/10.5376/jeb.2024.15.0009 Wang G., Yuan Z., Wang X., and Zhang G., 2023, Microbial conversion and utilization of CO2, Annals of Civil and Environmental Engineering, 7: 45-60. https://doi.org/10.29328/journal.acee.1001055 Wu H., Li Q., Li Z., and Ye Q., 2012, Succinic acid production and CO2 fixation using a metabolically engineered Escherichia coli in a bioreactor equipped with a self-inducing agitator, Bioresource technology, 107: 376-84. https://doi.org/10.1016/j.biortech.2011.12.043 Xiao K., Ge T., Wu X., Peacock C., Zhu Z., Peng J., Bao P., Wu J., and Zhu Y., 2020, Metagenomic and 14C tracing evidence for autotrophic microbial CO2 fixation in paddy soils, Environmental Microbiology, 23(2): 924-933. https://doi.org/10.1111/1462-2920.15204
Bioscience Evidence 2024, Vol.14, No.4, 143-153 http://bioscipublisher.com/index.php/be 153 Zhang L., Liu Y., Zhao R., Zhang C., Jiang W., and Gu Y., 2020, Interactive regulation of formate dehydrogenase during CO2 fixation in gas-fermenting bacteria, mBio, 11(4): 10-1128. https://doi.org/10.1128/mBio.00650-20 Zhang Q., Nurhayati, Cheng C., Nagarajan D., Chang J., Hu J., and Lee D., 2017, Carbon capture and utilization of fermentation CO2: Integrated ethanol fermentation and succinic acid production as an efficient platform, Applied Energy, 206: 364-371. https://doi.org/10.1016/j.apenergy.2017.08.193
Bioscience Evidence 2024, Vol.14, No.4, 154-160 http://bioscipublisher.com/index.php/be 154 Research Report Open Access Phytoremediation of Soil Contaminated with Lead (Pb) and Zinc (Zn) Using Chromolaena odorata(L.) under Greenhouse Condition O. M. Ajayi , O. Kekere Department of Pant Science and Biotechnology, Adekunle Ajasin University, P.M.B. 01, Akungba-Akoko, Ondo State, Nigeria Co-corresponding emails: otito.kekere@aaua.edu.ng; oluwaferanmiajayi2@gmail.com Bioscience Evidence, 2024, Vol.14, No.4 doi: 10.5376/be.2024.14.0017 Received: 29 Jun., 2024 Accepted: 22 Jul., 2024 Published: 13 Aug., 2024 Copyright © 2024 Ajayi and Kekere, This is an open access article published under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Preferred citation for this article: Ajayi O.M., and Kekere O., 2024, Phytoremediation of soil contaminated with lead (Pb) and zinc (Zn) using Chromolaena odorata (L.) under greenhouse condition, Bioscience Evidence, 14(4): 154-160 (doi: 10.5376/be.2024.14.0017) Abstract Phytoremediation is gaining popularity worldwide for its cost-effectiveness and environmentally friendly approach to removal of heavy metals from soil. This study investigated potential of weed, Chromolaena odorata (L.), in remediating soil contaminated with lead (Pb) and zinc (Zn). The experiment involved growing C. odorata as potted plants in soil with varying concentrations (0-100 mg/kg) of Pb and Zn. The survival of the seedlings was not affected by either heavy metal. Compared to the control, there was no significant effect of Pb on number of leaves at 20-60 mg/kg but significantly increased it at 80-100 mg/kg. Zn significantly reduced number of leaves at all the concentrations applied. Pb did not significantly affect stem girth while Zn led to its significant reduction at 60-100 mg/kg. Pb had no significant effect on leaf area except at 80 mg/kg where there was an increase, while it was not significantly affected by Zn. The metals decreased root length without statistical difference from the control while number of roots was not affected. Fresh and dry weight values of plant parts were higher under contamination than the control. This was significant at 80-100 mg/kg for leaf and stem, and at 80 mg/kg for root. The plant was more tolerant to Pb than Zn in growth. There were significantly higher concentrations of metals in plant parts of those grown in metal contaminated soil than the control. C. odoratais a potential candidate for phytoremediation of soil contaminated with Pb and Zn, and can survive up to 100 mg/kg. Keywords Siam weed; Heavy metals; Soil; Pollution; Remediation 1 Introduction The soil, recognized as a vital ecosystem, assumes critical roles in sustaining life, contributing to food production, climate regulation, and supplying raw materials essential for various human activities (Atagana, 2011; Ayesa et al., 2018). Despite its paramount importance, the integrity of the global soil environment faces formidable challenges due to escalating human activities that induce pollution (FAO, 2015a, http://www.fao.org/3/a-i4324e.pdf; FAO, 2015b, http://www.fao.org/3/a-i4965e.pdf; FAO, 2015c). Soil pollution, arising from the direct or indirect discharge of extraneous substances, poses significant threats to the delicate balance of living resources, human health, and environmental well-being (Masindi and Muedi, 2018). The cumulative impact of industrial and mining activities as well as some agricultural practices exacerbates soil pollution, with heavy metals assuming a predominant role as major culprits in this environmental challenge (EEA, 2014, https://www.eea.europa.eu/data-and-maps/indicators/progress-in-management-of-contaminated-sites/progress-inmanagement-ofcontaminated-1; Cetin, 2016; Sandeep et al., 2019). With the rapid development of economy and society, a variety of heavy metals contaminate soil which threatens the environment and public health (Lambert et al., 2012; Kapoor et al., 2021). Many of such metals including Pb and Zn are widely distributed, and persist long-term in soil environment. Soil contamination by heavy metals leads to decreasing availability of farmland as they negatively affect plant growth as well as crop yield (Yahaghi et al., 2019; Madhu and Sadagopan, 2020; Khan et al., 2023; Rashid et al., 2023). Besides, the metals may be accumulated into edible and non-edible parts of plants. Surveys have shown that continuous consumption of concentrations of heavy metals through foodstuffs lead to large accumulations of the metals in the kidney and liver of humans causing disruption of numerous body processes, leading to cardiovascular, nervous, kidney and bone diseases (Angon et al., 2024). Specifically, taking very high doses of Zn is likely unsafe and might cause stomach pain, vomiting, and many other problems. Single doses of 10-30 grams of zinc can be fatal (Herawati,
Bioscience Evidence 2024, Vol.14, No.4, 154-160 http://bioscipublisher.com/index.php/be 155 2000). When applied to the skin: Zn is likely unsafe. Using zinc on broken skin may cause burning, stinging, itching, and tingling. Similarly, Pb consumption is associated with great risk to brain development, where irreversible damage can occur. Higher levels can damage the kidney and nervous system in both children and adults. Very high lead levels may cause seizures, unconsciousness and death (Madhu and Sadagopan, 2020). The development and production of plants depend on several nutrients such as Mg, Cu, Mn, Zn, Fe, Ca, Mo and Ni. Some of these are micronutrients that can improve a variety of cellular processes in plants, including pigment biosynthesis, ion homeostasis, gene regulation, respiration, enzyme activity, sugar metabolism, photosynthesis, nitrogen fixation, etc., at relatively low concentrations (Tiwari and Lata, 2018). However, they can negatively impact plant growth, development and reproduction when they are accumulated at concentrations above their optimal levels (Rashid et al., 2023; Angon et al., 2024). Arsenic, cadmium, zinc and lead are among the prominent heavy metals identified as common pollutants, exerting adverse effects on the intricate interplay between soil health, plant vitality, and the overall well-being of human and animal populations (Herawati et al., 2000). Studies have shown that these heavy metals can persist in nature for more than twenty years (Kapoor and Singh, 2021), and the only solution is to remove them from soil to a permissible level for plants. According to Madhu and Sadagopan (2020), a lot of studies have been conducted on remediation techniques for heavy metal polluted soil, including in-situ remediation techniques (surface capping, encapsulation, electrokinetic extraction, soil flushing, chemical immobilization, phytoremediation or bioremediation) and ex-situ remediation techniques (landfilling, soil washing, solidification or vitrification). Although these methods have high performance, most of them are expensive, harmful to the environment and time-consuming. Phytoremediation has been identified for cost-effectiveness and environmentally friendly approach to removal of heavy metals from soil. It emerges as a widely accepted solution, utilizing the inherent capabilities of plants to degrade or remove pollutants from the soil environment (Haq et al., 2020; Islam et al., 2024). There are advantages of using phytoremediation. It is economically feasible as it is an autotrophic system powered by solar energy; it is simple to manage; and the cost of installation and maintenance is low. Also, it is eco-friendly as it can reduce exposure of the pollutants to the people and environment particular underground water. Chromolaena odorata (L.), commonly known as Siam weed is a fast-growing perennial, diffuse and scrambling shrub. It is an exotic weed that has become aggressively invasive in Nigeria. It forms dense stands and is a problem in agricultural land and commercial plantations causing great economic and biodiversity losses. It is found in disturbed areas, abandoned and waste lands, where there can be potentially high soil heavy metal contamination (Srirueang et al., 2022). It has been recorded to grow naturally in waste sites, hence it was hypothesised that it has some inherent ability for survival under toxic environment, which might include ability to absorb and sequester heavy metals without negative symptoms. The objective of the study was to assess the potential of C. odorata for phytoremediation of soil contaminated with lead (Pb) and zinc (Zn). This was hoped to contribute to the ongoing discourse surrounding sustainable and effective environmental remediation strategies. 2 Materials and Methods 2.1 Collection of soil used for planting Samples of the soil used for planting were analysed to know its physical and chemical properties. The samples were shade-dried, passed through a 2-mm sieve, and analyzed for physical and chemical properties using standard methods of the Association of Official Analytical Chemists (AOAC, 1990). 2.2 Experimental set up Uniform young seedlings of C. odorata were collected from a plantation site in Akure, Ondo State, Nigeria, and transplanted into polyethylene pots filled with top soil mixed with 0, 20, 40, 60, 80 and 100 mg ZnSO4 or PbSO4 to 1 kg soil (mg/kg Pb or Zn). The targeted concentrations fell within and above the permissible level for Pb (85 mg/kg) and Zn (50 mg/kg) in soil according to World Health Organization, WHO (1996). The experiment was conducted at the screen house of Plant Science and Biotechnology Department, Adekunle Ajasin University, Akungba-Akoko, Ondo State, Nigeria. During the experiment, the screen house had an average morning
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