Co-culture of Acetobacterium woodii and Clostridium drakei using CO₂ and in situ generated H₂ to produce caproic acid via lactic acid

Syngas fermentation processes have been proposed as promising technology for high value chemical production from one carbon compounds including CO2, reducing both direct carbon emissions and replacing fossil fuels as feedstock in the chemical industry. Among the potential microorganisms able to utilize CO2 as main carbon source, Acetobacterium woodii is one of the most extensively studied and is considered a model organism for acetogens. Its main metabolite is the rather low value product acetic acid; however, recent recombinant strains are capable of producing lactate from CO2 and H2. Using the chain-elongating bacteria Clostridium drakei, a synthetic co-culture has the potential to produce higher value products such as caproic acid. In this study, a synthetic co-culture with the acetogens Acetobacterium woodii and Clostridium drakei in a stirred tank bioreactor, using CO2 and H2 as substrates for the production of caproic acid via the intermediate lactate was successfully developed and established. The H2 for the process was generated in situ with an All-in-One electrode, which was designed for effective H2 generation in any standard bioreactor. Caproate concentrations reached a maximum concentration of 0.1 g/L and a yield from lactate of up to 0.2 g/g. The co-cultivation was found to be beneficial for Clostridium drakei as inhibiting effects observed in pure culture were not noticed during co-cultivations. For the development of the co-culture, both strains were characterized separately. The recently developed strain Acetobacterium woodii ΔlctBCD ΔpyrE [p83_PbgaL_NFP] was found to be the most promising in comparison to other Acetobacterium woodii strains, reaching 0.5 g/L of lactate in the bioelectrochemical system with a volumetric productivity of up to 0.2 g/L d. H2 supply limitation was identified as the major bottleneck for the fermentations with the All-in-One electrode, as conventional gas fermentations with the same Acetobacterium woodii strain yielded 8.1 g/L lactate with a volumetric productivity of up to 2.0 g/L d. Nonetheless, cathode surface enlargement and reduction of Faradaic losses or numbering-up of the All-in-One could increase H2 production and thus lactate production. To the author’s best knowledge, this is the first study to show data of Clostridium drakei cultivations in a stirred-tank bioreactor growing on lactate. The maximum caproate concentration added up to 1.5 g/L with a volumetric productivity of 0.7 g/L d. The inhibitory level of caproic acid was identified at 1.5 g/L. Lastly, a lactate dependent process control was developed for the co-cultivation process, which can adjust the H2 production rate dynamically depending on the lactate concentrations measured online during the cultivation.

Subjects

carbon capture

Acetobacterium woodii

Clostridium drakei

in situ electrolysis

co-culture

caproic acid

DDC Class

570: Life Sciences, Biology

Funding(s)

SPP 2170: Teilprojekt "CaproMix - Entwicklung neuer und definierter Co-Kulturen zur Bioproduktion von Capronsäure aus Kohlendioxid"

Funding Organisations

Deutsche Forschungsgemeinschaft (DFG)

More Funding Information

Fördernummer 427864786

Lizenz

https://creativecommons.org/licenses/by-nc/4.0/

Name

Herzog_Jan_Co-culture of Acetobacterium woodii and Clostridium drakei using CO2 and in situ generated H2 to produce caproic acid via lactic acid.pdf

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8.03 MB

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Adobe PDF

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Co-culture of Acetobacterium woodii and Clostridium drakei using CO₂ and in situ generated H₂ to produce caproic acid via lactic acid