Abstract
BackgroundSynthesis gas, a mixture of CO, H2, and CO2, is a promising renewable feedstock for bio-based production of organic chemicals. Production of medium-chain fatty acids can be performed via chain elongation, utilizing acetate and ethanol as main substrates. Acetate and ethanol are main products of syngas fermentation by acetogens. Therefore, syngas can be indirectly used as a substrate for the chain elongation process.ResultsHere, we report the establishment of a synthetic co-culture consisting of Clostridium autoethanogenum and Clostridium kluyveri. Together, these bacteria are capable of converting CO and syngas to a mixture of C4 and C6 fatty acids and their respective alcohols. The co-culture is able to grow using solely CO or syngas as a substrate, and presence of acetate significantly stimulated production rates. The co-culture produced butyrate and caproate at a rate of 8.5 ± 1.1 and 2.5 ± 0.63 mmol/l/day, respectively. Butanol and hexanol were produced at a rate of 3.5 ± 0.69 and 2.0 ± 0.46 mmol/l/day, respectively. The pH was found to be a major factor during cultivation, influencing the growth performance of the separate strains and caproate toxicity.ConclusionThis co-culture poses an alternative way to produce medium-chain fatty acids and higher alcohols from carbon monoxide or syngas and the process can be regarded as an integration of syngas fermentation and chain elongation in one growth vessel.
Highlights
Synthesis gas, a mixture of carbon monoxide (CO), H2, and carbon dioxide (CO2), is a promising renewable feedstock for bio-based production of organic chemicals
Pure cultures were incubated as follows: C. kluyveri was grown with 90 mM ethanol and 80 mM acetate in presence of 10 kPa CO2, and C. autoethanogenum was grown with 130 kPa CO as sole substrate
Trace amounts of butanol and hexanol were detected in the co-culture, while these compounds were not observed in any of the monocultures incubated with CO, acetate, and ethanol
Summary
A mixture of CO, H2, and CO2, is a promising renewable feedstock for bio-based production of organic chemicals. Production of medium-chain fatty acids can be performed via chain elongation, utilizing acetate and ethanol as main substrates. Bio-based production of medium-chain fatty acids (MCFA), such as butyrate and caproate, is of potential interest because they can serve as commodity. C. autoethanogenum is one of the model organisms for syngas metabolism and is known for its excellent properties to convert CO or syngas to ethanol and acetate (Table 1) [15]. C. kluyveri is found in ruminal environments [16], and is reported to stimulate the production of MCFA in the rumen [17] It represents a major fraction of microorganisms in systems performing chain elongation [18]. C. kluyveri is well known for its reversed β-oxidation metabolism, converting short chain fatty acids with ethanol into MCFA and hydrogen (Table 1). It could serve as a model and provide insight on how the carboxylate platform, operated with mixed cultures, performs using syngas as electron donor
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