Presentation Information
[2BRBP-07-KL]Toward process development of thermophilic gas fermentation for carbon recycling
○Yutaka Nakashimada1 (1. Hiroshima University (Japan))
Keywords:
Thermophilic gas fermentation,Moorella thermoacetica,Metabolic engineering of acetogens,Redox and energy balance,Gas–liquid mass transfer
The advancement of gas fermentation for carbon recycling critically depends on the development of microbial catalysts capable of efficiently converting gaseous substrates into valuable products. In particular, the design of thermophilic acetogens offers a promising route to expand both the metabolic potential and process efficiency of gas fermentation systems.
Our research focuses on strain engineering of the thermophilic acetogen Moorella thermoacetica, which grows at 50–60 oC and naturally utilizes syngas and H2/CO2 via the Wood–Ljungdahl pathway. Beyond its metabolic versatility, thermophilic operation provides a significant advantage in process design, enabling the integration of fermentation with in situ product recovery, especially for volatile compounds. This feature has the potential to reduce downstream separation costs and improve overall energy efficiency. To establish M. thermoacetica as a versatile production platform, we have developed a genetic engineering system and implemented metabolic engineering strategies to introduce non-native product pathways. Through these efforts, we successfully constructed strains capable of producing reduced chemicals such as ethanol, acetone, isopropanol, and acetoin with high selectivity.
A central outcome of our studies is the identification of key design principles governing product formation in acetogens. Efficient production of reduced compounds requires (i) precise control of intracellular redox balance and (ii) sufficient ATP supply to sustain energetically demanding biosynthetic pathways. These constraints are particularly pronounced in H2/CO2-based metabolism, where both reducing power and energy generation are limited.
To address this limitation, we explored metabolic configurations utilizing CO-containing gas streams. CO metabolism provides not only reducing equivalents via ferredoxin but also contributes to ATP generation through energy-conserving pathways. This dual role enables thermophilic acetogens to overcome intrinsic energetic constraints and supports the efficient synthesis of highly reduced products. Based on this concept, we designed strains in which redox flow is optimized to match the cofactor requirements of target pathways, resulting in high product selectivity.
While strain engineering defines the biochemical capability of gas fermentation, its realization ultimately depends on effective gas supply. Poor solubility of gaseous substrates such as H2 and CO imposes a fundamental limitation on reaction rates. In this regard, process development plays a supporting but indispensable role. The NEDO carbon recycling project at Osaki-Kamijima, Hiroshima provides a representative example, where mesophilic acetogens are operated on H2/CO2 with a strong focus on reactor design and gas–liquid mass transfer optimization.
From our perspective, such process innovations serve to unlock the full potential of engineered strains by ensuring sufficient substrate availability. Therefore, the development of advanced gas fermentation systems should be driven primarily by microbial design, complemented by process engineering that maximizes gas utilization.
This strain-centered approach, combined with rational process integration, provides a foundation for next-generation gas fermentation technologies capable of efficiently converting CO2 and syngas into a diverse range of valuable products.
Our research focuses on strain engineering of the thermophilic acetogen Moorella thermoacetica, which grows at 50–60 oC and naturally utilizes syngas and H2/CO2 via the Wood–Ljungdahl pathway. Beyond its metabolic versatility, thermophilic operation provides a significant advantage in process design, enabling the integration of fermentation with in situ product recovery, especially for volatile compounds. This feature has the potential to reduce downstream separation costs and improve overall energy efficiency. To establish M. thermoacetica as a versatile production platform, we have developed a genetic engineering system and implemented metabolic engineering strategies to introduce non-native product pathways. Through these efforts, we successfully constructed strains capable of producing reduced chemicals such as ethanol, acetone, isopropanol, and acetoin with high selectivity.
A central outcome of our studies is the identification of key design principles governing product formation in acetogens. Efficient production of reduced compounds requires (i) precise control of intracellular redox balance and (ii) sufficient ATP supply to sustain energetically demanding biosynthetic pathways. These constraints are particularly pronounced in H2/CO2-based metabolism, where both reducing power and energy generation are limited.
To address this limitation, we explored metabolic configurations utilizing CO-containing gas streams. CO metabolism provides not only reducing equivalents via ferredoxin but also contributes to ATP generation through energy-conserving pathways. This dual role enables thermophilic acetogens to overcome intrinsic energetic constraints and supports the efficient synthesis of highly reduced products. Based on this concept, we designed strains in which redox flow is optimized to match the cofactor requirements of target pathways, resulting in high product selectivity.
While strain engineering defines the biochemical capability of gas fermentation, its realization ultimately depends on effective gas supply. Poor solubility of gaseous substrates such as H2 and CO imposes a fundamental limitation on reaction rates. In this regard, process development plays a supporting but indispensable role. The NEDO carbon recycling project at Osaki-Kamijima, Hiroshima provides a representative example, where mesophilic acetogens are operated on H2/CO2 with a strong focus on reactor design and gas–liquid mass transfer optimization.
From our perspective, such process innovations serve to unlock the full potential of engineered strains by ensuring sufficient substrate availability. Therefore, the development of advanced gas fermentation systems should be driven primarily by microbial design, complemented by process engineering that maximizes gas utilization.
This strain-centered approach, combined with rational process integration, provides a foundation for next-generation gas fermentation technologies capable of efficiently converting CO2 and syngas into a diverse range of valuable products.
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