Human Gut Metagenomes Encode Diverse GH156 Sialidases

Area of Science:

• Microbiology
• Enzymology
• Human Microbiome Research

Background:

• The human gut microbiome utilizes glycoside hydrolases (GHs) to break down complex carbohydrates in the mucous barrier.
• Sialic acids are terminal sugars on host glycans, crucial for microbial interactions and host immunity.
• Sialidases, enzymes that cleave sialic acids, are known in the microbiome (GH33 family), but a broader exploration is needed.

Purpose of the Study:

• To investigate the presence and diversity of the GH156 sialidase family in the human gut microbiome.
• To characterize the enzymatic activity of novel GH156 sialidases from human gut samples.
• To explore the association of GH156 abundance and diversity with human populations and dietary practices.

Main Methods:

• Utilized hidden Markov models (HMMs) based on known GH156 sequences to search public databases.
• Analyzed metagenomic data from diverse human populations to assess GH156 gene prevalence.
• Recombinantly expressed and biochemically characterized five novel GH156 enzymes for sialidase activity.

Main Results:

• Identified approximately 10 times more putative GH156 sialidases than previously cataloged, including in key human gut phyla (Bacteroidota, Verrucomicrobiota, Firmicutes_A).
• Observed higher GH156 gene diversity and abundance in traditional hunter-gatherer/agriculturalist societies compared to industrialized ones, especially in individuals without inflammatory bowel disease (IBD).
• Confirmed sialidase activity for five newly identified gut-derived GH156 enzymes, demonstrating functional diversity within the family.

Conclusions:

• The GH156 sialidase family represents a significant, previously underappreciated component of the human gut microbiome.
• Dietary practices and societal factors influence the composition and abundance of GH156 enzymes in the gut.
• These novel GH156 sialidases expand the known repertoire of enzymes involved in host glycan degradation and hold potential for biotechnological and clinical applications.