A Novel D-Galacturonate Fermentation Pathway in Lactobacillus suebicus Links Initial Reactions of the Galacturonate-Isomerase Route With the Phosphoketolase Pathway
| Autor: | Martin Pabst, Marijke A. H. Luttik, Mark C.M. van Loosdrecht, Laura C. Valk, Marcel van den Broek, C. de Ram, Jack T. Pronk |
|---|---|
| Jazyk: | angličtina |
| Rok vydání: | 2020 |
| Předmět: |
Microbiology (medical)
Entner–Doudoroff pathway enrichment cultivation Phosphoketolase lcsh:QR1-502 Isomerase Microbiology lcsh:Microbiology Metabolic engineering 03 medical and health sciences pectin degradation galacturonic acid 030304 developmental biology 2. Zero hunger chemistry.chemical_classification 0303 health sciences 030306 microbiology Catabolism Chemistry heterolactic fermentation food and beverages Metabolism anaerobic metabolism Enzyme Biochemistry Fermentation |
| Zdroj: | Frontiers in Microbiology, Vol 10 (2020) Frontiers in Microbiology, 10 |
| ISSN: | 1664-302X |
| DOI: | 10.3389/fmicb.2019.03027/full |
| Popis: | D-galacturonate, a key constituent of pectin, is a ubiquitous monomer in plant biomass. Anaerobic, fermentative conversion of D-galacturonate is therefore relevant in natural environments as well as in microbial processes for microbial conversion of pectin-containing agricultural residues. In currently known microorganisms that anaerobically ferment D-galacturonate, its catabolism occurs via the galacturonate-isomerase pathway. Redox-cofactor balancing in this pathway strongly constrains the possible range of products generated from anaerobic D-galacturonate fermentation, resulting in acetate as the predominant organic fermentation product. To explore metabolic diversity of microbial D-galacturonate fermentation, anaerobic enrichment cultures were performed at pH 4. Anaerobic batch and chemostat cultures of a dominant Lactobacillus suebicus strain isolated from these enrichment cultures produced near-equimolar amounts of lactate and acetate from D-galacturonate. A combination of whole-genome sequence analysis, quantitative proteomics, enzyme activity assays in cell extracts, and in vitro product identification demonstrated that D-galacturonate metabolism in L. suebicus occurs via a novel pathway. In this pathway, mannonate generated by the initial reactions of the canonical isomerase pathway is converted to 6-phosphogluconate by two novel biochemical reactions, catalyzed by a mannonate kinase and a 6-phosphomannonate 2-epimerase. Further catabolism of 6-phosphogluconate then proceeds via known reactions of the phosphoketolase pathway. In contrast to the classical isomerase pathway for D-galacturonate catabolism, the novel pathway enables redox-cofactor-neutral conversion of D-galacturonate to ribulose-5-phosphate. While further research is required to identify the structural genes encoding the key enzymes for the novel pathway, its redox-cofactor coupling is highly interesting for metabolic engineering of microbial cell factories for conversion of pectin-containing feedstocks into added-value fermentation products such as ethanol or lactate. This study illustrates the potential of microbial enrichment cultivation to identify novel pathways for the conversion of environmentally and industrially relevant compounds. |
| Databáze: | OpenAIRE |
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