Project: Coral-microbial interactions as determinants of disease dynamics

Description from NSF award abstract:
The health of numerous animal and plant hosts depends on the composition of their microbiome. Although the health of hosts is often linked to environmental factors that favor the growth of pathogenic microbes, the diversity of animal and plant microbiomes suggests that competition plays an important role in determining the frequency and severity of disease outbreaks. This project uses the endangered Caribbean staghorn coral as a model system to understand how the environment and microbial interactions controls the spread of White Band Disease (WBD), a bacterial disease that has decimated nearly 95% of Caribbean staghorn coral populations. A combination of manipulative experiments, field surveys and mathematical modeling will be used to determine how water temperature, microbial movement between- and microbial competition within coral hosts influence WBD incidence. By identifying the environmental and microbial drivers of WBD, this project will allow managers to (i) predict hotspots of vulnerability to WBD in space and time, and (ii) identify optimal strategies for restoring these once prominent members of Caribbean coral reef communities. This research will address important societal needs by cross-training graduate students in coral biology, microbial genetics, bioinformatics, mathematical modeling, computer programming and statistics. Results of this project will be integrated into undergraduate courses in genetics, ecological modeling and biostatistics in order to emphasize the importance of quantitative and interdisciplinary STEM training for addressing important questions in biology. Finally, a series of interactive web modules will be created to disseminate the results of this project beyond academic circles, including to Northeastern University's Marine Science Center K-12 outreach programs and the Smithsonian Tropical Research Institute's outreach programs in Panama.

There is growing recognition that the processes that structure microbial communities may scale up to explain disease outbreaks in their hosts. Despite the complexity of microbial communities, most studies to date have focused on resolving the direct relationship between the environment, the occurrence of pathogenic microbes, and the incidence of disease. However, the effects of microbial species interactions and dispersal on the emergence of host diseases remain largely unknown. This project will combine microbial genetics and mathematical modeling to understand the relative influence of the environment, species interactions and dispersal on the structure of microbial communities and the dynamics of disease in their coral hosts. This research uses the endangered Caribbean staghorn coral (Acropora cervicornis) and White Band Disease (WBD) as a model host-pathogen system. This once dominant, reef-building coral was decimated by WBD, prompting its listing as an endangered species. Recent work in this system suggests that (i) bacteria are the cause of WBD, (ii) the microbial community living within the host can produce antibiotic compounds that suppress pathogenic bacteria, and (iii) temperature increase promotes infection and reduces the production of antibiotic compounds. These findings suggest that the interplay between the environment and host-associated microbial species determines the structure of the microbial community and the health of the coral host. To disentangle these processes, a multi-factorial transmission experiment will be conducted to understand the direct and indirect effects of temperature, pathogen exposure, and microbial community complexity on disease dynamics. To determine how these results scale up to natural coral reefs, a spatial coral-microbial model will be fitted to field survey data. This fitted model will elucidate how seasonal temperature variation and microbial dispersal jointly influence coral disease outbreaks and the structure of coral-microbial communities across spatial scales. The proposed research will integrate research with teaching and training of undergraduate students.