The horse gut microbiota genome represents a vast novel reservoir of CAZymes.

Overview

• This study explores the gut microbiome of horses to uncover a vast diversity of carbohydrate-active enzymes (CAZymes), which are crucial for breaking down plant polysaccharides.
• The researchers identified a novel enzyme with potential applications in biotechnology, highlighting the horse gut as a rich source for discovering new biocatalysts.

Introduction and Background

• Herbivores rely on their gut microbiota to digest plant material, which is rich in complex carbohydrates.
• Carbohydrate-active enzymes (CAZymes) such as glycoside hydrolases (GHs) and glycosyl transferases (GTs) are essential for breaking down these polysaccharides into usable forms.
• Mining gut microbiomes from herbivores is a promising approach to discovering efficient and novel CAZymes for industrial and biotechnological applications.

Research Approach and Methods

• The study analyzed 12,763 metagenome-assembled genomes (MAGs) derived from the horse gut microbiota to characterize CAZyme diversity.
• Computational methods were used to identify and quantify different CAZyme families, particularly glycoside hydrolases (GHs) and glycosyl transferases (GTs).
• Focus was placed on polysaccharide utilization loci (PULs), which are genomic regions coding for enzymes and transporters involved in polysaccharide degradation.
• Hypothetical genes located within PULs were screened for potential novel CAZyme candidates.
• One enzyme candidate named H113 was selected for experimental validation based on predicted function.

Key Findings

• The horse gut microbiome contained over 5.2 million glycoside hydrolases (GHs) and approximately 4.6 million glycosyl transferases (GTs), indicating a vast enzymatic potential.
• Bacteroidota and Bacillota_A were identified as the main bacterial phyla harboring the majority of CAZymes involved in plant polysaccharide degradation.
• A total of 17,250 PULs were discovered within Bacteroides species, underscoring their role in carbohydrate metabolism.
• Screening identified 12,976 hypothetical genes within PULs that represent putative novel CAZymes, expanding the known enzyme repertoire.
• The enzyme H113 was experimentally characterized:
  • Composed of 452 amino acids.
  • A metal-dependent enzyme with Zn ions significantly enhancing catalytic activity.
  • Capable of degrading α-1,4 glycosidic bonds in maltotriose and also active toward mannan polysaccharides.
  • Optimal activity occurred at pH 4.8 and 35°C.
  • Measured specific activities: 82.2 U/mg for maltotriose and 2.3 U/mg for mannan.
  • Phylogenetic analysis placed H113 in a conserved enzyme family with 1866 homologues, suggesting evolutionary conservation and broad functional relevance.

Implications and Significance

• The horse gut microbiota is confirmed as an exceptionally rich reservoir of CAZymes, offering extensive genetic diversity for carbohydrate degradation enzymes.
• This study provides a large-scale genomic resource and sets a framework for mining novel CAZymes from gut microbiomes of herbivores.
• The identification and biochemical validation of H113 demonstrate the potential to discover enzymes with unique properties suitable for industrial biocatalysis.
• Such enzymes could be applied in biofuel production, food industry, and other biotechnology sectors requiring efficient carbohydrate breakdown.
• The discovery expands scientific understanding of microbial polysaccharide degradation and the evolutionary distribution of these enzymes.

Conclusions

• By leveraging metagenomic data, the research uncovers an unprecedentedly large and novel set of CAZymes from the horse gut microbiome.
• The approach of combining genomic mining with functional validation is effective for identifying promising candidate enzymes.
• The study bridges basic microbial ecology with applied enzyme biotechnology, highlighting the relevance of gut microbiomes as sources of novel enzymes.