TY - JOUR
T1 - Galacturonate metabolism in anaerobic chemostat enrichment cultures
T2 - Combined fermentation and acetogenesis by the dominant sp. nov. "Candidatus Galacturonibacter soehngenii."
AU - Valk, Laura C.
AU - Frank, Jeroen
AU - de la Torre-Cortés, Pilar
AU - van 't Hof, Max
AU - van Maris, Antonius J.A.
AU - Pronk, Jack T.
AU - van Loosdrecht, Mark C.M.
PY - 2018
Y1 - 2018
N2 - 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 pectinrich 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 H2 as coproducts. The observed molar ratio of acetate and the combined amounts of H2 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.
AB - 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 pectinrich 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 H2 as coproducts. The observed molar ratio of acetate and the combined amounts of H2 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.
KW - Acetogenesis
KW - Enrichment culture
KW - Fermentation
KW - Galacturonate
KW - Metagenomics
UR - http://www.scopus.com/inward/record.url?scp=85053464359&partnerID=8YFLogxK
U2 - 10.1128/AEM.01370-18
DO - 10.1128/AEM.01370-18
M3 - Article
AN - SCOPUS:85053464359
SN - 0099-2240
VL - 84
JO - Applied and Environmental Microbiology
JF - Applied and Environmental Microbiology
IS - 18
M1 - e01370-18
ER -