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Title: The Isolate Caproiciproducens sp. 7D4C2 Produces n-Caproate at Mildly Acidic Conditions From Hexoses: Genome and rBOX Comparison With Related Strains and Chain-Elongating Bacteria
Authors: Esquivel-Elizondo, Sofia
Bağcı, C.
Temovska, Monika
Jeon, Byoung Seung
Bessarab, Irina 
Williams, Rohan B. H. 
Huson, Daniel H. 
Angenent, Largus T.
Keywords: Caproiciproducens
chain elongation
chain-elongating bacteria
rBOX genes
reverse β-oxidation
Issue Date: 14-Jan-2021
Publisher: Frontiers Media S.A.
Citation: Esquivel-Elizondo, Sofia, Bağcı, C., Temovska, Monika, Jeon, Byoung Seung, Bessarab, Irina, Williams, Rohan B. H., Huson, Daniel H., Angenent, Largus T. (2021-01-14). The Isolate Caproiciproducens sp. 7D4C2 Produces n-Caproate at Mildly Acidic Conditions From Hexoses: Genome and rBOX Comparison With Related Strains and Chain-Elongating Bacteria. Frontiers in Microbiology 11 : 594524. ScholarBank@NUS Repository.
Rights: Attribution 4.0 International
Abstract: Bulk production of medium-chain carboxylates (MCCs) with 6–12 carbon atoms is of great interest to biotechnology. Open cultures (e.g., reactor microbiomes) have been utilized to generate MCCs in bioreactors. When in-line MCC extraction and prevention of product inhibition is required, the bioreactors have been operated at mildly acidic pH (5.0–5.5). However, model chain-elongating bacteria grow optimally at neutral pH values. Here, we isolated a chain-elongating bacterium (strain 7D4C2) that grows at mildly acidic pH. We studied its metabolism and compared its whole genome and the reverse β-oxidation (rBOX) genes to other bacteria. Strain 7D4C2 produces lactate, acetate, n-butyrate, n-caproate, biomass, and H2/CO2 from hexoses. With only fructose as substrate (pH 5.5), the maximum n-caproate specificity (i.e., products per other carboxylates produced) was 60.9 ± 1.5%. However, this was considerably higher at 83.1 ± 0.44% when both fructose and n-butyrate (electron acceptor) were combined as a substrate. A comparison of 7D4C2 cultures with fructose and n-butyrate with an increasing pH value from 4.5 to 9.0 showed a decreasing n-caproate specificity from ∼92% at mildly acidic pH (pH 4.5-5.0) to ∼24% at alkaline pH (pH 9.0). Moreover, when carboxylates were extracted from the broth (undissociated n-caproic acid was ∼0.3 mM), the n-caproate selectivity (i.e., product per substrate fed) was 42.6 ± 19.0% higher compared to 7D4C2 cultures without extraction. Based on the 16S rRNA gene sequence, strain 7D4C2 is most closely related to the isolates Caproicibacter fermentans (99.5%) and Caproiciproducens galactitolivorans (94.7%), which are chain-elongating bacteria that are also capable of lactate production. Whole-genome analyses indicate that strain 7D4C2, C. fermentans, and C. galactitolivorans belong to the same genus of Caproiciproducens. Their rBOX genes are conserved and located next to each other, forming a gene cluster, which is different than for other chain-elongating bacteria such as Megasphaera spp. In conclusion, Caproiciproducens spp., comprising strain 7D4C2, C. fermentans, C. galactitolivorans, and several unclassified strains, are chain-elongating bacteria that encode a highly conserved rBOX gene cluster. Caproiciproducens sp. 7D4C2 (DSM 110548) was studied here to understand n-caproate production better at mildly acidic pH within microbiomes and has the additional potential as a pure-culture production strain to convert sugars into n-caproate. © Copyright © 2021 Esquivel-Elizondo, Bağcı, Temovska, Jeon, Bessarab, Williams, Huson and Angenent.
Source Title: Frontiers in Microbiology
ISSN: 1664-302X
DOI: 10.3389/fmicb.2020.594524
Rights: Attribution 4.0 International
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