Although numerous efforts have been made to engineer acetogens to produce various biochemicals from C1 gases, these studies have been limited to a small-scale. Among the native metabolites produced from acetogens, acetate, ethanol, and 2,3-butanediol (2,3-BDO) have been produced by C1 gas fermentation on an industrial scale using a non-engineered strain of Clostridium autoethanogenum ( Marcellin et al., 2016). Numerous studies have utilized acetogens as biocatalysts to convert C1 gases into value-added chemicals ( Berzin et al., 2012, 2013 Köpke et al., 2012 Banerjee et al., 2014 Beck et al., 2014 Woolston et al., 2018 Annan et al., 2019 Huang et al., 2019 Jin et al., 2020 Bae et al., 2022 Liew et al., 2022). In addition, it is the only pathway for CO 2 fixation coupled with an energy conservation system that plays a crucial role in generating cellular energy and sustaining life ( Schuchmann and Müller, 2014). Of the CO 2-fixing pathways known to date, the WL pathway is considered the most energetically efficient ( Fast et al., 2015 Claassens et al., 2019). They are facultative autotrophs that fix CO 2 and CO as carbon or energy sources via the unique metabolic pathway, the Wood–Ljungdahl (WL) pathway ( Ragsdale and Pierce, 2008 Drake et al., 2013). C1 gases are utilized by microbes as feedstocks and finally converted to value-added chemicals under mild conditions that are required for the optimal growth of microbes.Īcetogenic bacteria (acetogens) are promising platform microbes for C1 gas fixation. This is a preferable approach, because it does not require high pressure, temperature, cost, and energy, unlike chemical catalysts, such as in the Fischer–Tropsch process ( Latif et al., 2014 Dürre, 2017 Köpke and Simpson, 2020). To make the earth a sustainable place, reducing emissions is crucial, and urgent solutions for carbon capturing, utilization, and storage are needed.Ĭ1 gas fermentation could be a solution, which utilizes microbes as biocatalysts. C1 gases such as carbon dioxide (CO 2) and carbon monoxide (CO), which constitute greenhouse gases, industrial waste gases, and synthesis gases (syngas), are the main culprits of the climate crisis ( Anwar et al., 2018 Ritchie and Roser, 2020). The rapid increase in fossil fuel usage and greenhouse gas emissions has caused one of the biggest problems for humankind today. Future prospective approaches on engineering acetogens based on systems and synthetic biology approaches are also discussed. Supplying liquid C1 substrates, which can be obtained from CO 2, or electricity is introduced as a strategy to overcome the energy limitation. This review provides strategies for developing efficient platform strains for C1 gas conversion, focusing on engineering the WL pathway. The energy limitation of acetogens is one of the challenges to overcome, as their metabolism operates at a thermodynamic limit, and the low solubility of gaseous substrates results in a limited supply of cellular energy. Although some metabolites have been produced via C1 gas fermentation on an industrial scale, the conversion of C1 gases to produce various biochemicals by engineering acetogens has been limited. Acetogenic bacteria (acetogens) have received attention as high-potential biocatalysts owing to their conserved Wood–Ljungdahl (WL) pathway, which fixes not only CO 2 but also CO. Among them, the use of microorganisms as biocatalysts to convert C1 gases to value-added chemicals is a promising solution. Numerous studies have been conducted to fix and recycle C1 gases in order to solve this problem. 2KI for the BioCentury, Korea Advanced Institute of Science and Technology, Daejeon, South KoreaĬ1 gases, including carbon dioxide (CO 2) and carbon monoxide (CO), are major contributors to climate crisis.1Department of Biological Sciences, Korea Advanced Institute of Science and Technology, Daejeon, South Korea.Hyeonsik Lee 1 †, Jiyun Bae 1 †, Sangrak Jin 1 †, Seulgi Kang 1 and Byung-Kwan Cho 1,2 *
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