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Emergence of pathogenicity in the sea: altered host-microbe interactions in the face of environmental change

Periodic Reporting for period 1 - MICROCHANGE (Emergence of pathogenicity in the sea: altered host-microbe interactions in the face of environmental change)

Période du rapport: 2015-08-01 au 2017-07-31

Diseases are omnipresent in aquatic ecosystems but there are numerous signs that some parts of our oceans/freshwater systems are more affected. The number of disease outbreaks in marine organisms is increasing in several key groups of marine animals, which include marine mammals and corals, but other less well-studied organisms may be equally affected. Also unprecedented mass mortality and rapid disappearance of once-common species imply an unbalanced system or an introduced pathogen, or both. As causes for the outbreak of marine diseases strong environmental drivers are key, such as eutrophication (sewage and agricultural runoff) or rising global temperatures (climate change) but also pollution, invasion of new/exotic species, and destruction of coastal habitats can serve as stresses that interact in complex ways with the microbiota and their hosts. Diseases in some marine animals affect humans directly, for example through cultural or economic costs – others more indirectly through the degradation of ecosystem productivity.

Animals and plants form a distinct habitat for microbial communities (microbiomes), and these microbial associations are integral to life. Host-associated communities colonize every accessible host tissue, have an impact on host function and contribute to host fitness and health. There is accumulating evidence from studies that show links between diseases and the diversity of an organism’s microbiome. Disturbing the balance between the host and its colonizing microbiota appears to foster diseases. Vibrios are important bacterial pathogens for animals reared in aquaculture but are at the same time symbionts of several vertebrate and invertebrate hosts, such as fish, sea anemones, sponges, molluscs, and zooplankton.

The objective of the project was to gain a better understanding of how environmental stress affects the assembly of host-associated microbial communities and how these host-associated communities influence disease emergence.
Changes in microbiome diversity, function and density have been linked to a variety of disorders in many organisms. After exposing cnidarians to nutrient enriched environments, we followed changes in the microbiome composition and density and monitored host health. 16S rRNA gene high-throughput Illumina sequencing was used to assess microbiota composition and plating for determining host microbial densities over time. The implications from this study are that microbial population density is a fundamental parameter in understanding host health, and that nutritional stress contributes to alterations in the microbiome that may be linked to the deterioration of host health, potentially also through pathogen emergence.

As microbiomes consist of many interacting species one also has to decipher the types of interactions at play to understand the ecology of microbiomes and how they respond to stress. Here I studied the interactions between two bacterial strains and their fitness in host and host-free environments. Findings include that microbial fitness is key, as it will yield insights into the role that microbes played not only in the evolution of eukaryotes, but also into the ecology and evolution of host-microbe associations in general and the evolution of pathogen emergence.

Results from this project will help to close the knowledge gap from microbiome composition to ecological interactions within these communities and help to untangle how environmental change drives host-microbiome dynamics and disease emergence. For conservation, aquaculture, human and animal health alike, understanding what threatens these interactions is essential.

Dissemination of research findings was done through scientific publications (5 to this point) and presentations at conferences (total of 9).
"This project will contribute to further ensure high food and environmental standards in EU countries. In a recent White Paper on adapting to climate change it was highlighted the need ""to promote strategies which increase the resilience to climate change of health, property and the productive functions of land, inter alia by improving the management of water resources and ecosystems"". To achieve this goal fundamental knowledge on the underlying processes that take place is necessary and this project contributes a small part in the puzzle.
Right on our doorstep we can observe links between environmental changes, including temperature increase, and enhanced disease expression. Abnormally high temperatures in the Baltic Sea area coincide with unusually large numbers of Vibrio infections. Understanding these links falls within the EuroMarine vision Blue Science for Blue Growth where complementing activities have been funded.

Results from my current and also previous research support the notion that the microbiome also has significant implications for conservation biology. Concepts and methods of microbiome research could therefore be applied to meet conservation challenges such as captive breeding, inbreeding, reintroduction, invasion of non-native species, habitat fragmentation, and change in climate. Successful management of endangered species may well require managing their microbiomes.
The EU Biodiversity Strategy aims to protect the natural capital essentials to our health and our economy by halting the loss of biodiversity and ecosystem services in the EU. Several strategies have been developed including species protection. Managing micorobiomes/microbiome engineering my therefore aid in protecting animals (and plants) facing certain threats in Europe.
Host-associated microbial communities are shaped by complex interactions between microorganisms and