Hyeonsik Lee

Bio: Hyeonsik Lee is an academic researcher from KAIST. The author has contributed to research in topics: Medicine & Biochemical engineering. The author has an hindex of 1, co-authored 1 publications receiving 6 citations.

Engineering Acetogenic Bacteria for Efficient One-Carbon Utilization

Abstract: C1 gases, including carbon dioxide (CO2) and carbon monoxide (CO), are major contributors to climate crisis. Numerous studies have been conducted to fix and recycle C1 gases in order to solve this problem. Among them, the use of microorganisms as biocatalysts to convert C1 gases to value-added chemicals is a promising solution. Acetogenic bacteria (acetogens) have received attention as high-potential biocatalysts owing to their conserved Wood–Ljungdahl (WL) pathway, which fixes not only CO2 but also CO. 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. 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. This review provides strategies for developing efficient platform strains for C1 gas conversion, focusing on engineering the WL pathway. Supplying liquid C1 substrates, which can be obtained from CO2, or electricity is introduced as a strategy to overcome the energy limitation. Future prospective approaches on engineering acetogens based on systems and synthetic biology approaches are also discussed.

Genome-wide CRISPRi screen identifies enhanced autolithotrophic phenotypes in acetogenic bacterium Eubacterium limosum

Abstract: Significance Acetogenic bacteria can fix approximately 20% of the atmosphere’s carbon and reduce C1 feedstocks, such as CO2 or CO, to multicarbon compounds via the Wood–Ljungdahl pathway, thus playing a prominent role in the global carbon cycle. Using a CRISPR interference (CRISPRi) screen, we measured gene fitness at the genome level under heterotrophic and autotrophic growth conditions and demonstrated a strategy to increase the autotrophic growth rate on the basis of this dataset. Our findings can contribute to advancing the understanding of acetogenesis metabolism and further engineering a cell factory system for the sustainable production of value-added chemicals from industrial waste gases.

Effect of the Reducing Agent Dithiothreitol on Ethanol and Acetic Acid Production by Clostridium Strain P11

Abstract: The effect of dithiothreitol (DTT) on enhancing ethanol production from syngas using Clostridium strain P11 was investigated in 250-mL serum bottles. Reducing agents help in regeneration of NADH from NAD+. NADH is utilized in the production of alcohol from aldehydes. Strain P11 was fed with syngas every 24 h and samples were collected to measure pH, cell mass and product concentrations. Various concentrations of DTT were examined. Results showed over fourfold increase in ethanol production in media that contained at least 7.5 g/L of DTT after 360 h of fermentation compared to the control medium (without DTT). Similar pH, cell mass and acetic acid profiles were observed in the control and DTT media. The results suggested that the use of small concentrations of DTT in the broth enhances ethanol production from syngas, which is an important factor towards making gasification-fermentation technology an economically viable process.

Reactor Designs and Configurations for Biological and Bioelectrochemical C1 Gas Conversion: A Review.

Abstract: Microbial C1 gas conversion technologies have developed into a potentially promising technology for converting waste gases (CO2, CO) into chemicals, fuels, and other materials. However, the mass transfer constraint of these poorly soluble substrates to microorganisms is an important challenge to maximize the efficiencies of the processes. These technologies have attracted significant scientific interest in recent years, and many reactor designs have been explored. Syngas fermentation and hydrogenotrophic methanation use molecular hydrogen as an electron donor. Furthermore, the sequestration of CO2 and the generation of valuable chemicals through the application of a biocathode in bioelectrochemical cells have been evaluated for their great potential to contribute to sustainability. Through a process termed microbial chain elongation, the product portfolio from C1 gas conversion may be expanded further by carefully driving microorganisms to perform acetogenesis, solventogenesis, and reverse β-oxidation. The purpose of this review is to provide an overview of the various kinds of bioreactors that are employed in these microbial C1 conversion processes.