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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - RAVE (Rotifers as Vehicles for Epibiotic Bacteria)

Teaser

Summary

Non-trophic species interactions such as epibiosis are poorly studied and their impact on ecosystem properties not easily quantified. Using bacterial communities on biofilms attached to freshwater microscopic animals and to other substrates as a model system, the RAVE project targeted several hypotheses on epibiosis and biofilm interactions in freshwater systems.
The work moved along three steps: (1) descriptive surveys of the patterns in the field, (2) experimental manipulations, and (3) generalisations of the results.
The project followed a bottom-up approach from field surveys, through experimental assessments of specific hypotheses, to the statistical inference on the different questions. The questions were addressed by state-of-the-art methodologies (e.g. chemostat experiments, high throughput sequencing, and appropriate statistical models) by combining the expertise of microbial ecologists, evolutionary ecologists, and zoologists. The cross-disciplinary approach of RAVE deepened our understanding in the field of microbial interactions in biofilms.

Work performed

The first step was to understand whether epibionts are host specific. Using extensive field data, we demonstrated that the bacterial communities associated to rotifers, cladocerans, copepods, sediments, stones, and in water at different depths in a lake were coherently similar within and significantly different between substrates.
Then, we explored the degree of association between the microbiota and the hosts: we found that for cladocerans, copepods, and cyanobacteria such association is present, whereas no association was found for rotifers. We highlighted unexpected differences in the host-epibiont relationships.
After the descriptive part to explore the degree of association, we moved to more functional analyses, analysing potential processes driving the presence of bacteria on biofilms and the role they have in the potential spread of pathogens and/or antibiotic resistance genes. We used different models systems, including bacteria associated to zooplankton, in biofilms associated to living organisms (e.g. rotifers, crustaceans, corals, etc.), in biofilms on microplastics, etc. We discovered that:
- cladocerans can act as a refuge for antibiotic resistance genes selected under anthropogenic pressure;
- biofilms on microplastics increase the potential for the spread of antibiotic resistance;
- anthropogenic pollution and ecological factors interact in driving the persistence of antibiotic resistance genes in freshwater environments and in host-associated biofilms;
- microbial associations interfere with the recruitment of coral colonies;
- species coexistence and predation may promote microbial diversity;
- antibiotic disturbance affects aquatic microbial community composition and phenotypic distribution of cells but not diversity and stability of the communities
For each of the main results we obtained we prepared scientific manuscripts for submission. Some of them are already accepted, and others are still under review. Most of the results were also presented at international conferences to allow a broad range of researchers getting in contact with us. Moreover, we presented some of the results during local events and conferences to the public at our host institute in Verbania Pallanza, Italy. All the genetic information produced during the project was deposited or will be deposited in online repositories, e.g. GenBank.

Final results

The project highlighted the underappreciated role of ecological interactions in the spread of antibiotic resistance genes in bacteria, one of the major concerns for the future of public health. Thus, our results will be pivotal in driving economic, political, and societal decisions on the management and conservation of aquatic ecosystems with the aim of minimising risks for people due to antibiotic resistant bacteria, while preserving natural diversity.