Mucus layer properties and dynamics in reef corals

Abstract

Mucus functions as the first line of defence against infections, amongst other roles. The protective role of mucus depends upon gel-forming properties of mucin molecules that are encoded by the MUC genes. Failure of this protective barrier has been associated with changes in structure, function and physical properties of mucins in human diseases (cancer, IBD and cystic fibrosis) and has been proposed as a prognostic tool for early diagnosis of these diseases. The study of coral mucus is in its infancy and early investigations on coral mucus gave incomplete and variable chemical composition data. The dynamic nature of the coral surface mucus layer (SML) in limiting pathogens remains unexplored. The present study attempts to detect coral muc genes by tracing the evolution of muc genes from cnidarians to mammals using bioinformatics tools, examines the coral mucin molecule and investigates the response of epidermal and surface mucus to the changing environmental conditions. The presence of a continuous SML at least 145 μm thick on the coral epithelium has been demonstrated for the first time. Rheological studies confirmed the presence of high molecular weight, polymeric glycoprotein similar to mammalian mucin. The study has also developed molecular tools (primers) based on bioinformatics information and has detected tandem repeats rich in serine, threonine and proline and C-terminal Cysteine Knot regions homologous to those of human gel forming mucins. A variation in the epidermal mucus content as well as SML was noticed in between the species as a response to bleaching (loss of zooxanthellae and complete white appearance of coral tissue) and changing environmental conditions (tidal cycle). Thus, study of mucus indicates the health of corals and plays an important role in survival of coral during diseases and environmental stressful conditions.