Enzymatic Mechanism by Which Dolphin Gut Microbes Degrade Plant Polysaccharides Unveiled
Symbiotic microbial groups within the digestive tract of herbivores are the main source of depolymerized lignocellulases. The dolphin is the largest extant rodent, usually living in the Pantanal wetland and Amazon basin, and is also known as the "king of grass" due to its diet based on grasses and aquatic plants. They can efficiently depolymerize and utilize lignocellulosic biomass through microbial symbiotic mechanisms. Recently, a research paper published in Nat Commun entitled "Gut microbiome of the largest living rodent harbors unprecedented enzymatic systems to degrade plant polysaccharides" specifically studied the enzymatic strategies and metabolic pathways used by dolphins to decompose their microbial symbiotic communities of dietary fiber.
The researchers used 16S rRNA gene targeted sequencing (16S), meta-genomics (MG), meta-transcriptomics (MT), and nuclear magnetic resonance metabolomics (NMR) to comprehensively study dolphin gut bacteria. Studies have found that the taxonomic structure of intestinal bacteria in the cecum and rectum of dolphins is mainly dominated by bacteria, while archaea and fungi account for a small proportion. The most abundant bacteria in the microbial community were from Firmicutes and Bacteroidetes, followed by Fusobacteria and Proteobacteria. Reconstructed meta-genome assembly genomes (MAGs) were used to discover some unknown species or genera of known plant fiber-degrading bacteriaceae (e.g., Cellulobacteraceae and Bacteroidaceae). MAGs of dolphin gut bacteria contain the highest number of genes encoding hydrocarbon enzymes (CAZymes), which may be involved in the depolymerization of different hemicelluloses (including heteroxylans). These studies suggest that there may be untapped, high-performance molecular systems in the dolphin gut microbiota for plant fiber breakdown and utilization.
In addition, it has been found that Fibrobacter and Bacteroidetes are the main degraders of dietary fiber in the intestine of dolphins. CAZyome analysis of dolphin gut microbes showed that Cellulobacter was the main driver of cellulolysis, while a large number of Bacteroidetes and CAZymes communities provided a large number of enzymatic strategies for dolphin communities to digest hemicellulose and pectin in food.
The researchers further investigated the role of these microorganisms in the conversion of free sugars into energy using integrated metabolomics and metabolic reconstitution analysis. Studies have found that the main fermentation products in the intestine of dolphins are short-chain fatty acids (SCFAs), which are the main energy source of the host, indicating that the intestinal microbial population produces energy metabolites for the host while decomposing plant polysaccharides. In addition, the researchers found a family of glycoside hydrolases (named GH173) and a family of carbohydrate-binding modules (named CBM89) of β-galactosidase, which are involved in xylan binding and establish an unprecedented three-dimensional fold of carbohydrate-active enzymes between related modules.
Together, these results illustrate how the dolphin gut microbiota coordinates the depolymerization and utilization of plant fibers to overcome the intractability of lignocellulose and lay the foundation for high value-added product development of lignocellulosic agro-industrial materials.
Collected by CD BioGlyco, a biotechnology company that provides a full range of glycobiology-related products, analysis, custom synthesis, and design to advance glycobiology research. The company also provides Plant Polysaccharides Separation, and Plant Polysaccharides Structure Analysis for research use.