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Title: “Candidatus Paraporphyromonas polyenzymogenes” encodes multi-modular cellulases linked to the type IX secretion system

Abstract. Background In nature, obligate herbivorous ruminants have a close symbiotic relationship with their gastrointestinal microbiome, which proficiently deconstructs plant biomass. Despite decades of research, lignocellulose degradation in the rumen has thus far been attributed to a limited number of culturable microorganisms. Here in this paper, we combine meta-omics and enzymology to identify and describe a novel Bacteroidetes family (“Candidatus MH11”) composed entirely of uncultivated strains that are predominant in ruminants and only distantly related to previously characterized taxa. Results. The first metabolic reconstruction of Ca. MH11-affiliated genome bins, with a particular focus on the provisionally named “Candidatus Paraporphyromonas polyenzymogenes”, illustrated their capacity to degrade various lignocellulosic substrates via comprehensive inventories of singular and multi-modular carbohydrate active enzymes (CAZymes). Closer examination revealed an absence of archetypical polysaccharide utilization loci found in human gut microbiota. Instead, we identified many multi-modular CAZymes putatively secreted via the Bacteroidetes-specific type IX secretion system (T9SS). This included cellulases with two or more catalytic domains, which are modular arrangements that are unique to Bacteroidetes species studied to date. Core metabolic proteins from Ca. P. polyenzymogenes were detected in metaproteomic data and were enriched in rumen-incubated plant biomass, indicating that active saccharification and fermentation of complex carbohydratesmore » could be assigned to members of this novel family. Biochemical analysis of selected Ca. P. polyenzymogenes CAZymes further iterated the cellulolytic activity of this hitherto uncultured bacterium towards linear polymers, such as amorphous and crystalline cellulose as well as mixed linkage β-glucans. Conclusion. We propose that Ca. P. polyenzymogene genotypes and other Ca. MH11 members actively degrade plant biomass in the rumen of cows, sheep and most likely other ruminants, utilizing singular and multi-domain catalytic CAZymes secreted through the T9SS. The discovery of a prominent role of multi-modular cellulases in the Gram-negative Bacteroidetes, together with similar findings for Gram-positive cellulosomal bacteria (Ruminococcus flavefaciens) and anaerobic fungi (Orpinomyces sp.), suggests that complex enzymes are essential and have evolved within all major cellulolytic dominions inherent to the rumen.« less
 [1] ;  [2] ;  [3] ;  [3] ;  [1] ;  [1] ;  [4] ;  [5] ;  [3] ;  [1] ;  [1] ;  [6] ;  [7] ;  [2] ;  [1]
  1. Norwegian Univ. of Life Sciences (NMBU), As (Norway). Faculty of Chemistry, Biotechnology and Food Science
  2. The Ohio State Univ., Columbus, OH (United States). Dept of Microbiology
  3. Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab. (EMSL)
  4. Helmholtz Centre for Infection Research, Braunschweig (Germany). Computational Biology of Infection Research
  5. Univ. of Illinois, Urbana-Champaign, IL (United States). Inst. for Genomic Biology and Dept. of Animal Sciences
  6. Univ. of Michigan, Ann Arbor, MI (United States). Medical School, Dept. of Microbiology and Immunology
  7. Univ. of California, Davis, CA (United States). Dept. of Animal Science
Publication Date:
Report Number(s):
Journal ID: ISSN 2049-2618; PII: 421
Grant/Contract Number:
AC05-76RL01830; AC02-06CH11357; 336355-MicroDE
Accepted Manuscript
Journal Name:
Additional Journal Information:
Journal Volume: 6; Journal Issue: 1; Journal ID: ISSN 2049-2618
BioMed Central
Research Org:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org:
USDOE; Research Council of Norway; European Research Council (ERC)
Country of Publication:
United States
59 BASIC BIOLOGICAL SCIENCES; Type IX secretion system; Carbohydrate-active enzymes; Cellulases; Bacteroidetes
OSTI Identifier: