Enhancing hydrogen‐dependent growth of and carbon dioxide fixation by Clostridium ljungdahlii through nitrate supplementation. Issue 2 (9th December 2018)

• Record Type: Journal Article
• Authors: Emerson, David F.; Woolston, Benjamin M.; Liu, Nian; Donnelly, Mackenzie; Currie, Devin H.; Stephanopoulos, Gregory
• Is Part Of: Biotechnology and bioengineering. Volume 116:Issue 2(2019)
• Page Start: 294
• Page End: 306
• Publication Date: 2018-12-09
• Subjects: acetogenic bacteria -- anaerobic respiration -- Clostridium ljungdahlii -- fixation -- hydrogen -- nitrate; Biotechnology -- Periodicals; Bioengineering -- Periodicals; 660.6
• DOI: 10.1002/bit.26847
• Languages: English
• ISSNs: 0006-3592

Abstract

Abstract: Synthesis gas (syngas) fermentation via the Wood–Ljungdahl pathway is receiving growing attention as a possible platform for the fixation of CO 2 and renewable production of fuels and chemicals. However, the pathway operates near the thermodynamic limit of life, resulting in minimal adenosine triphosphate (ATP) production and long doubling times. This calls into question the feasibility of producing high‐energy compounds at industrially relevant levels. In this study, we investigated the possibility of co‐utilizing nitrate as an inexpensive additional electron acceptor to enhance ATP production during H 2 ‐dependent growth of Clostridium ljungdahlii, Moorella thermoacetica, and Acetobacterium woodii . In contrast to other acetogens tested, growth rate and final biomass titer were improved for C. ljungdahlii growing on a mixture of H 2 and CO 2 when supplemented with nitrate. Transcriptomic analysis, 13 CO 2 labeling, and an electron balance were used to understand how electron flux was partitioned between CO 2 and nitrate. We further show that, with nitrate supplementation, the ATP/adenosine diphosphate (ADP) ratio and acetyl‐CoA pools were increased by fivefold and threefold, respectively, suggesting that this strategy could be useful for the production of ATP‐intensive heterologous products from acetyl‐CoA. Finally, we propose a pathway for enhanced ATP production from nitrate and use this as a basis to calculate theoretical yields for a variety of products. This study demonstrates a viable strategy for the decoupling of ATP production from carbon dioxide fixation, which will serve to significantly improve the CO 2 fixation rate and the production metrics of other chemicals from CO 2 and H 2 in this host. Abstract : CO2 fixation with H2 by acetogens operates near the thermodynamic limit, resulting in high yields but slow doubling times of around 20 hrs. Unlike other acetogens, Clostridium ljungdahlii reduced nitrate while fixing CO2 ; the presence of nitrate resulted in large increases to growth rate and yield. Furthermore, the ATP/ADP ratio and acetyl‐CoA pool size were increased by 5‐fold and 3‐fold, respectively; these results highlight the benefit nitrate could provide for the production of energy‐intensive heterologous products.