Date of Award
Coral reefs are essential ecosystems that provide an abundance of natural resources. Sponges, common reef inhabitants, produce a diversity of secondary metabolites that are known to serve as chemical defenses. Secondary metabolites often have ecological functions, such as antipredator and antibacterial activities. I studied the common Caribbean sponge species, Amphimedon compressa, which is known to be chemically defended. Samples were collected from three sites in Belize, two sites in Grand Cayman, and three sites in St. Croix, U.S. Virgin Islands. To determine whether antibacterial activity varied across broad or local geographic scales, sponge extracts were tested against four bacterial strains that included coral and human pathogens. Antibacterial assays compared the degree of growth inhibition by the sponge extracts. In addition, extracts from healthy tissue samples from both healthy sponges and sponges affected by sponge white patch disease were tested to assess any variation in extract concentration and antibacterial activity with sponge condition. Extracts from A. compressa inhibited all the bacterial strains tested, but there was selective antibacterial activity against the different bacterial strains. In general, A. coralicida, a Caribbean coral pathogen, was most strongly inhibited, whereas V. coralliilyticus, an Indo-Pacific coral pathogen, was least inhibited. I found no variation in extract concentrations at local or broad geographic scales. Antibacterial activity differed between countries and sites within countries, and there were significant interactions between the bacterial strains and sites in Belize and St. Croix, resulting in different geographic patterns against the different bacteria. Sponge extracts from healthy and diseased sponges showed no difference in extract concentration or level of antibacterial activity. These results indicate that A. compressa has strong antibacterial chemical defenses that vary geographically, and disease has no impact on the antibacterial activity of the remaining healthy tissue. Further studies must be conducted to determine the specific chemicals responsible for antibacterial activity and the factors responsible for the geographic variation.
Reilly, Mackenzie, "Variability in Antibacterial Activity in the Caribbean Sponge Amphimedon compressa" (2020). Honors Theses. 1368.
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