Enhancing CO₂-valorization using Clostridium autoethanogenum for sustainable fuel and chemicals production

Abstract

20Acetogenic bacteria can convert waste gases into fuels and chemicals. Design of 21 bioprocesses for waste carbon valorization requires quantification of steady-state carbon 22 flows. Here, steady-state quantification of autotrophic chemostats containing 23Clostridium autoethanogenum grown on CO2 and H2 revealed that captured carbon (460 24 ± 80 mmol/gDCW/day) had a significant distribution to ethanol (54 ± 3 mol% with a 252.4 ± 0.3 g/L titer). We were impressed with this initial result, but also observed 26 limitations to biomass concentration and growth rate. Metabolic modelling predicted 27 culture performance and indicated significant metabolic adjustments when compared to 28 fermentation with CO as the carbon source. Moreover, modelling highlighted flux to 29 pyruvate, and subsequently reduced ferredoxin, as a target for improving CO2 and H2 30 fermentation. Supplementation with a small amount of CO enabled co-utilisation with 31 CO2, and enhanced CO2 fermentation performance significantly, while maintaining an 32 industrially relevant product profile. Additionally, the highest specific flux through the 33 Wood-Ljungdahl pathway was observed during co-utilization of CO2 and CO.

Towards continuous industrial bioprocessing with solventogenic and acetogenic clostridia: challenges, progress and perspectives

“…Ethanol is a desired product and formed acetate leaving the process is considered a “carbon loss” [ 301 ]. Several omics studies hence investigated the influence of the pH-value and substrate limitation [ 249 ] or the composition of the feed gas [ 106 , 299 , 300 , 340 ] on ethanol formation. One interesting finding of proteome studies is that an increase in ethanol production seems not to be linked to key enzyme abundance in both C. ljungdahlii [ 249 ] and C. autoethanogenum [ 299 ], suggesting that regulation might be thermodynamically or on a posttranslational level rather than on a transcriptional level.…”

“…Further tools including plasmid systems for gene overexpression, dCas9 and RNA systems for gene down-regulation and gene deletion and insertion tools are reviewed elsewhere [ 37 , 135 , 166 , 195 ]. An impressive testimony for the importance and applicability of genetic engineering of anaerobic microorganisms is the custom-made ‘Clostridia Biofoundry’ for fully automated, high throughput strain engineering used by the commercial syngas fermenting company LanzaTech [ 106 ].…”

Synthetic Biology on Acetogenic Bacteria for Highly Efficient Conversion of C1 Gases to Biochemicals

“…GEMs contain the entire set of known biochemical reactions taking place in an organism and allow us to predict, in silico, the flux distribution across the metabolic pathway. Based on in silico simulation/analysis using GEMs, the carbon flux or energy balance of acetogens during C1 fixation could be better understood [ 37 , 89 , 91 , 113 , 114 , 115 , 116 , 117 ]. This large amount of information based on systems biology can help understand the genetic regulation system for the C1 fixation process of acetogens.…”

Sustainable Production of Microbial Isoprenoid Derived Advanced Biojet Fuels Using Different Generation Feedstocks: A Review

“…Other microorganisms with potential as third and fourth generation feedstocks include acetogens such as Clostridium autoethanogenum, which are capable of producing ethanol from syngas and industrial waste gasses (Heffernan et al, 2020). Such organisms provide a means of capturing and recycling carbon from waste gases that would otherwise be released into the atmosphere and contribute to environmental pollution.…”

“…Lanzatech are striving to capitalize on the potential of the species to develop wide-ranging sustainable fuels and chemicals (LanzaTech, 2017). They recently commercialized an innovative waste gas to bioethanol process using C. autoethanogenum (Heffernan et al, 2020). The company have also successfully engineered the species for the production of farnesene from a carbon monoxide containing waste gas (Yiting Chen et al, 2015).…”