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Galacturonate Metabolism in Anaerobic Chemostat Enrichment Cultures: Combined Fermentation and Acetogenesis by the Dominant sp nov "Candidatus Galacturonibacter soehngenii"
Delft Univ Technol, Dept Biotechnol, Delft, Netherlands..
Radboud Univ Nijmegen, Soehngen Inst Anaerob Microbiol, Nijmegen, Netherlands..
Delft Univ Technol, Dept Biotechnol, Delft, Netherlands..
Delft Univ Technol, Dept Biotechnol, Delft, Netherlands..
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2018 (English)In: Applied and Environmental Microbiology, ISSN 0099-2240, E-ISSN 1098-5336, Vol. 84, no 18, article id UNSP e01370-18Article in journal (Refereed) Published
Abstract [en]

Agricultural residues such as sugar beet pulp and citrus peel are rich in pectin, which contains galacturonic acid as a main monomer. Pectin-rich residues are underexploited as feedstocks for production of bulk chemicals or biofuels. The anaerobic, fermentative conversion of D-galacturonate in anaerobic chemostat enrichment cultures provides valuable information toward valorization of these pectin-rich feedstocks. Replicate anaerobic chemostat enrichments, with D-galacturonate as the sole limiting carbon source and inoculum from cow rumen content and rotting orange peels, yielded stable microbial communities, which were dominated by a novel Lachnospiraceae species, for which the name "Candidatus Galacturonibacter soehngenii" was proposed. Acetate was the dominant catabolic product, with formate and H-2 as coproducts. The observed molar ratio of acetate and the combined amounts of H-2 and formate deviated significantly from 1, which suggested that some of the hydrogen and CO2 formed during D-galacturonate fermentation was converted into acetate via the Wood-Ljungdahl acetogenesis pathway. Indeed, metagenomic analysis of the enrichment cultures indicated that the genome of "Candidatus G. soehngenii" encoded enzymes of the adapted Entner-Doudoroff pathway for D-galacturonate metabolism as well as enzymes of the Wood-Ljungdahl pathway. The simultaneous operation of these pathways may provide a selective advantage under D-galacturonate-limited conditions by enabling a higher specific ATP production rate and lower residual D-galacturonate concentration than would be possible with a strictly fermentative metabolism of this carbon and energy source. IMPORTANCE This study on D-galacturonate metabolism by open, mixed-culture enrichments under anaerobic, D-galacturonate-limited chemostat conditions shows a stable and efficient fermentation of D-galacturonate into acetate as the dominant organic fermentation product. This fermentation stoichiometry and population analyses provide a valuable baseline for interpretation of the conversion of pectin-rich agricultural feedstocks by mixed microbial cultures. Moreover, the results of this study provide a reference for studies on the microbial metabolism of D-galacturonate under different cultivation regimes.

Place, publisher, year, edition, pages
American Society for Microbiology , 2018. Vol. 84, no 18, article id UNSP e01370-18
Keywords [en]
acetogenesis, enrichment culture, fermentation, galacturonate, metagenomics
National Category
Microbiology
Identifiers
URN: urn:nbn:se:kth:diva-235115DOI: 10.1128/AEM.01370-18ISI: 000443291000033PubMedID: 29959255Scopus ID: 2-s2.0-85053464359OAI: oai:DiVA.org:kth-235115DiVA, id: diva2:1249542
Note

QC 20180919

Available from: 2018-09-19 Created: 2018-09-19 Last updated: 2020-03-09Bibliographically approved

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van Maris, Antonius J. A.

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