Interactions of Mucus Monosaccharides and the Epidermal Microbiome in Four Benthic Elasmobranchs

Epidermal mucus is a complicated mixture of macromolecules which acts as the first line of defence for organisms against abrasions and infections. We quantified the carbohydrate (monosaccharide) composition of the mucus from four Elasmobranchii hosts, including eagle rays (Myliobatis tenuicaudatus), Port Jackson sharks (Heterodontus portusjacksoni), Australian angelsharks (Squatina australis) and whitespotted skates (Dentiraja cerva). Elasmobranchii had low amounts of mucus and a low proportion of carbohydrates (< 10%) compared with other marine organisms. Four key monosaccharides: glucose, glucosamine, galactose and fucose, were identified in mucus samples. Hosts exhibited distinct, species-specific monosaccharide signatures. We identified key carbohydrate microbial genes from host and water microbiomes. Elasmobranch microbiomes had a higher relative abundance of carbon utilisation genes compared to the water column and contained gene pathways for the utilisation of specific monosaccharides found in host mucus, suggesting that the host mucus was a regulator of the microbiome. Elasmobranch epidermal microbiomes have the genetic machinery required for detecting, transporting and metabolising monosaccharides and other carbohydrates present in the host mucus, demonstrating the selective nature of Elasmobranch epidermal mucus.