Thermoanaerobacter species differ in their potential to reduce organic acids to their corresponding alcohols

• Published in: Applied microbiology and biotechnology Vol. 102; no. 19; pp. 8465 - 8476
• Main Authors: Hitschler, Lisa, Kuntz, Michelle, Langschied, Felix, Basen, Mirko
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01-10-2018; Springer; Springer Nature B.V
• Subjects: Acids; Alcohol; Alcohols; Alcohols - metabolism; Aldehyde dehydrogenase; Aldehyde Dehydrogenase - genetics; Aldehyde Dehydrogenase - metabolism; Aldehyde Oxidoreductases - genetics; Aldehyde Oxidoreductases - metabolism; Aldehydes; Applied Microbial and Cell Physiology; Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Biomedical and Life Sciences; Biotechnology; Catalysis; Clonal deletion; Direct reduction; Enzymatic activity; Ethanol; Ethanol - metabolism; Ferredoxin; Gene deletion; Genetic modification; Genome, Bacterial; Genomes; Hyperthermophiles; Life Sciences; Microbial Genetics and Genomics; Microbiology; NADH; Nicotinamide adenine dinucleotide; Organic acids; Oxidoreductase; Species; Species Specificity; Strains (organisms); Sugar; Thermoanaerobacter - classification; Thermoanaerobacter - metabolism; Bio-alcohol production; Organic acid reduction; Aldehyde:ferredoxin oxidoreductase; Thermoanaerobacter
• ISSN: 0175-7598; 1432-0614
• DOI: 10.1007/s00253-018-9210-3

The reduction of organic acids to their corresponding alcohols has been shown for some bacterial species within the Firmicutes super-phylum and a genetically modified strain of the hyperthermophilic archaeon
Pyrococcus furiosus
. In the latter strain, an aldehyde:ferredoxin oxidoreductase (AOR) catalyzed the reduction of a variety of organic acids to their corresponding aldehydes, as shown by the deletion of the corresponding
aor
gene. Here, we found that the genomes of a few thermophilic bacterial species within the genus
Thermoanaerobacter
which have been described to efficiently ferment sugars to ethanol harbor a copy of
aor
, while others do not. Specific AOR activity was only found in strains with
aor
, and the gene was highly expressed in
Thermoanaerobacter
sp. strain X514. The reduction of a variety of organic acids was observed for several
Thermoanaerobacter
sp.; however, strains with
aor
reduced, e.g., isobutyrate at much higher rates of up to 5.1 mM h
−1
 g
−1
. Organic acid reduction also led to increased growth rates in
Thermoanaerobacter
sp. strain X514 and in
Thermoanaerobacter pseudethanolicus
. Organic acid activation may proceed via acyl-CoA with subsequent NADH-dependent reduction by an aldehyde dehydrogenase (ALDH), or via direct reduction by AOR. Cell-free extracts of
Thermoanaerobacter
sp. strain X514 exhibited both enzyme activities at comparable rates. Therefore, the biochemistry of organic acid reduction to alcohols in
Thermoanaerobacter
sp. remains to be elucidated; however, relatively high specific activities and the correlation of AOR specific activities with alcohol production rates suggest a role for AOR.