Bacterial Distribution in the Epidermis and Mucus of the Coral Euphyllia glabrescens by CARD-FISH

The distribution of bacteria in coral mucus has long been poorly understood, although most coral-associated bacteria were suggested to dwell in the mucus and epidermis of corals. We hypothesized that different bacterial groups have different distribution patterns in the mucus and epidermis. To test this hypothesis, we overcame technical difficulties of mucus preservation during sample preparation and inspected the distributions of 2 dominant coral-associated bacterial groups, the alphaproteobacteria and gammaproteobacteria, in the mucus and epidermis of the coral, Euphyllia glabrescens, collected from Kenting and Ludao (also known as Green I.) in southern Taiwan. We used catalyzed reporter deposition-fluorescence in situ hybridization to detect the location of the bacteria in the mucus and epidermis, and results showed that the 2 bacterial groups had different distribution patterns in the coral. Alphaproteobacteria were frequently distributed at the interface between the mucus and epidermis, while gammaproteobacteria were only detected in the gastrodermis and rarely observed in the mucus or epidermis. This study provides the 1st direct evidence that different bacterial groups have habitat specificity in coral mucus.