"Candidatus Paraporphyromonas polyenzymogenes" encodes multi-modular cellulases linked to the type IX secretion...

Area of Science:

• Microbial Ecology
• Biochemistry
• Genomics

Background:

• Ruminants rely on gut microbes for plant biomass digestion.
• Lignocellulose degradation in ruminants is poorly understood, with few identified microbes.
• A novel, uncultivated Bacteroidetes family, "Candidatus MH11," is prevalent in ruminant guts.

Purpose of the Study:

• To identify and characterize novel microorganisms involved in lignocellulose degradation in ruminants.
• To investigate the enzymatic machinery of uncultivated bacteria in the rumen microbiome.

Main Methods:

• Meta-omics (genomics, metaproteomics) to analyze microbial communities and functions.
• Enzymology to assess the activity of carbohydrate-active enzymes (CAZymes).
• Metabolic reconstruction of microbial genomes.

Main Results:

• "Candidatus Paraporphyromonas polyenzymogenes" (Ca. P. polyenzymogenes) possesses extensive CAZyme inventories for lignocellulose breakdown.
• Ca. P. polyenzymogenes utilizes a unique Type IX Secretion System (T9SS) to secrete multi-modular CAZymes, including novel cellulases.
• Metaproteomic data confirmed active protein production and enrichment in plant biomass, linking Ca. P. polyenzymogenes to saccharification.

Conclusions:

• "Candidatus MH11" members, particularly Ca. P. polyenzymogenes, are key players in ruminant plant biomass degradation.
• The study reveals the significant role of multi-modular enzymes secreted via T9SS in Bacteroidetes for cellulose breakdown.
• Complex enzymatic strategies have evolved across different microbial groups (Bacteroidetes, Gram-positive bacteria, fungi) in the rumen for efficient lignocellulose digestion.