Insights into the Structure and Function of the Gut Metagenome in Cartilaginous Fishes

Abstract

Across environments, the cycling of nutrients is supported by a variety of reactions catalyzed by microorganisms. The carbon (C) cycling specifically relies on the processing of plant polysaccharides (e.g. cellulose) in land ecosystems and animal/fungal-derived polysaccharides (e.g. chitin) in terrestrial and marine ecosystems. These processes are catalyzed by carbohydrate-active enzymes (CAZymes) of microbial origin, notably glycoside hydrolases (GHs).

This thesis elucidates the connection between host development, subsequent dietary shifts and the impact of these shifts on diet on the structure and function of the gut microbial community. Microbiome functional genome suggests that horn sharks appeared to eat less arthropods and more chordates as they developed, whereas shovelnose guitarfish ate more arthropods and less chordates with increasing body length (cm). These dietary changes were reflected by changes in GH frequencies, specifically GHs involved in the degradation of chitin (i.e. GH18, GH19). Though GH frequencies remained constant in the horn shark gut microbiome, chitinase frequencies (i.e. GH18, GH19) increased with increasing shovelnose guitarfish body length (cm). This approach allowed me to further clarify the relationship between the development and feeding habits of wild, sympatric fishes and the structure function of the gut microbial communities. Illuminating the precise enzymatic contribution of the microbial community in local nutrient cycling is a prerequisite to unraveling the microbial contribution to ecosystem health and global nutrient cycling.