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Title: PRJEB18125      
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Background: Syngas fermentations with pure microbial cultures currently results in ethanol/acetic acid mixtures as product. Ethanol has a low market value and is traditionally purified through an energy-intensive distillation, which reduces overall profitability when waste heat is not available. These issues could be circumvented by implementing a biological chain that converts the dilute ethanol/acetic acid mixtures to longer, easier to extract products that attract higher value. Chain elongation has been studied using reactor microbiomes that convert complex organic waste streams to medium chain carboxylic acids (MCCAs). Few studies exist with pure microbial cultures as a biotechnology production platform. The upgrading of syngas fermentation effluent with pure cultures has not yet been shown. Results: Here, we focus on the use of pure cultures of C. kluyveri to convert ethanol/acetic acid mixtures to MCCAs. We describe the operation of two continuous bioreactors and factors influencing the productivity of the culture, such as organic loading rate (OLR), presence or absence of in-line product extraction, and pH. Increased loading rates resulted in proportionally higher volumetric production rates of n-caproic acid, up to 40 mM·d-1 (4.64 g·L-1·d-1) and carbon conversion efficiencies of 90% or higher. Also caprylic acid production was observed for the first time with this organism (up to 2.19 ± 0.34 mM in batch). The use of real effluent from syngas fermentation, without added yeast extract, did not decrease productivities. The metabolism of C. kluyveri was however inhibited at the low pH values (5.50) for which reactor microbiomes were successfully elongating. Conclusions: Overall, we show that syngas fermentation effluent can be converted to MCCAs under defined conditions, but several challenges remain for the use of C. kluyveri as a production strain.
ID:
PRJEB18125
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landingpage: http://www.ncbi.nlm.nih.gov/bioproject/PRJEB18125
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abbreviation:
NCBI
homePage: http://www.ncbi.nlm.nih.gov
ID:
SCR:006472
name:
National Center for Biotechnology Information
homePage: http://www.ncbi.nlm.nih.gov/bioproject
ID:
SCR:004801
name:
NCBI BioProject