Abstract
The bioprocessing of amino acids to branched-chain fatty acids and alcohols is described using Thermoanaerobacter strain AK85. The amino acid utilization profile was evaluated without an electron scavenger, with thiosulfate, and in a co-culture with a methanogen. There was an emphasis on the production of branched-chain alcohols and fatty acids from the branched-chain amino acids, particularly the influence of culture conditions which was investigated using isoleucine, which revealed that the concentration of thiosulfate was of great importance for the branched-chain alcohols/fatty acid ratio produced. Kinetic studies show that branched-chain amino acid fermentation is relatively slow as compared to glucose metabolism with the concentrations of the branched-chain alcohol increasing over time. To understand the flow of electrons and to investigate if the branched-chain fatty acid was being converted to branched-chain alcohol, enzyme assays and fermentation studies using 13C-labeled leucine and 3-methyl-1-butyrate were performed which indeed suggest that carboxylic acid reduction is a source of branched-chain alcohols when Thermoanaerobacter strain AK85 was cultivated with thiosulfate as an electron scavenger.
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Abbreviations
- AA:
-
Amino acid
- ADH:
-
Alcohol dehydrogenase
- AOR:
-
Aldehyde oxidase
- BCAA:
-
Branched-chain amino acid
- BCFA:
-
Branched-chain fatty acid
- BCOH:
-
Branched-chain alcohol
- BM:
-
Basal mineral medium
- Ile:
-
Isoleucine
- Leu:
-
Leucine
- NMR:
-
Nuclear magnetic resonance
- Val:
-
Valine
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Acknowledgements
The authors gratefully acknowledge financial support from Landsvirkjun, Reykjavik, Iceland (project number NÝR-08-2015). The authors appreciate the support of Sigríður Jónsdóttir of the Science Institute at the University of Iceland for her assistance with obtaining NMR spectra.
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Supplementary Fig. 1 Fermentation kinetics of Thermoanaerobacter strain AK85 grown on of 20 mM Valine (A), 20 mM Leucine (B) in the presence of thiosulfate (20 mM). Values represent the average of triplicate fermentations with standard deviation presented as error bars (DOCX 29 kb)
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Scully, S.M., Orlygsson, J. Branched-chain amino acid catabolism of Thermoanaerobacter strain AK85 and the influence of culture conditions on branched-chain alcohol formation. Amino Acids 51, 1039–1054 (2019). https://doi.org/10.1007/s00726-019-02744-z
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DOI: https://doi.org/10.1007/s00726-019-02744-z