Exploring the functions of coral-associated bacteria in the holobiont stress response with natural probiotics (MicroFun)

• Applicant: Professorin Dr. Maren Ziegler
• Subject Area: Microbial Ecology and Applied Microbiology ; Oceanography
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 525433352

Coral reefs are complex and biodiverse, and they are among the most vulnerable ecosystems to climate change. As global warming continues, it is of utmost urgency to understand the mechanisms that influence the thermal tolerance of corals, the keystone species of the coral reef. Previous work implicates the microbiome as key player in coral environmental tolerance. The realization, that functions provided by microbiota may enhance coral holobiont performance, has shaped the emerging concept of “Beneficial Microorganisms for Corals” (BMC). BMC, delivered as probiotic cocktail, can improve the health outcome under heat stress. However, four major knowledge gaps hamper our understanding of the complex functions of coral-associated bacteria in stress tolerance: First, even though the importance of bacteria to coral holobiont homeostasis is now undisputed, the mechanisms by which they contribute to holobiont health and how they act in the stress response remain largely unknown. Second, BMC are an effective treatment to reduce the stress response, but we lack a mechanistic proof for their mode of action and functions. Third, multiple stressors affect coral reefs at the same time, but whether the same microbial functions may mediate the impacts of different stressors is largely unexplored. Last, most BMC studies focus on a single coral species, so that it is currently unknown if the microbial functions of BMC from one coral species may mitigate the stress response of other coral species. This project will close these knowledge gaps by combining analyses of microbial functions in corals of different health states, bacterial culturing, and an experiment on climate change and BMC application with three coral species. Its major goal is to unravel the complex roles of microbial functions in determining the stress tolerance of corals (MicroFun). The project is split into three work packages: (1) Characterization of bacterial functions of healthy and stressed corals with high and low heat stress tolerance using microbial metagenomics. (2) Isolation of bacterial taxa from these coral holobionts followed by integrated phenotypic, whole-genome-based, and metabolomic analyses to unlock the functional repertoire of the coral-associated microbiome. The created biobank of cultures will be used to assemble a BMC cocktail for further experimentation. (3) A combined heat and pCO2 stress experiment using three coral species with crossed BMC cocktails. This project will provide fundamental insights into the mechanisms of the coral holobiont stress response and the microbial functions that play a key role in increasing their tolerance. The proposed activities will further elucidate the potential and application of BMCs as coral probiotics to manipulate microbial functions, and to fast-track coral adaptation to and recovery from climate change.

• DFG Programme: Research Grants
• Co-Investigator: Dr. Krupali Poharkar