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Aquatic ecosystems at risk for occurrence of pathogenic bacteria
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
Division of CBRN Defence and Security, Swedish Defence Research Agency, FOI, SE-901 82 Umeå, Sweden.
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.ORCID iD: 0000-0001-5601-9358
Division of CBRN Defence and Security, Swedish Defence Research Agency, FOI, SE-901 82 Umeå, Sweden.
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Pathogenic bacteria occur naturally in aquatic systems. Co-existence of bacteria and protozoa has led to development of predation resistance strategies, which is suggested to serve as a driver for evolution of pathogenic bacteria. However, the ecological mechanisms for selection for different types of predation resistant and pathogenic bacteria are poorly known. To disentangle effects from nutrient availability and protozoan predation pressure on the occurrence of varying predation resistant bacterial genera, an enrichment-dilution experiment was performed where an aquatic bacterial community was exposed to protozoa. Operational taxonomical units, specific for three predation resistant bacterial genera were identified; Pseudomonas, Rickettsia and Mycobacterium. These genera are also known to harbor species that are potentially pathogenic to mammals. Rickettsia and Mycobacterium were promoted where protozoa were abundant and the predation pressure high, while Pseudomonas dominated the bacterial community at the highest nutrient level where the predation pressure on bacteria were low. Our study thus indicates that waters of all nutrient states can harbor pathogenic bacteria, but that bacteria with different ecological strategies occur depending on nutrient level and perturbation. The generative model approach presented here provide a possibility to integrate environmental data in prediction models of pathogens in complex environments.

Keyword [en]
Protozoa resistant bacteria, predation pressure, aquatic bacterial pathogens, risk assessment, microcosm experiment
National Category
Ecology
Identifiers
URN: urn:nbn:se:umu:diva-133336OAI: oai:DiVA.org:umu-133336DiVA: diva2:1087104
Funder
Ecosystem dynamics in the Baltic Sea in a changing climate perspective - ECOCHANGESwedish Research Council for Environment, Agricultural Sciences and Spatial Planning, 217-2008-1443Swedish Research Council, 60276201
Note

Medfinansiär var även: The Swedish Ministry of Defence [A404217]

Available from: 2017-04-05 Created: 2017-04-05 Last updated: 2017-04-06
In thesis
1. Environmental factors selecting for predation resistant and potentially pathogenic bacteria in aquatic environments
Open this publication in new window or tab >>Environmental factors selecting for predation resistant and potentially pathogenic bacteria in aquatic environments
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The long history of co-existence of bacteria and their protozoan predators in aquatic environments has led to evolution of protozoa resistant bacteria (PRB). Many of these bacteria are also pathogenic to humans. However, the ecological drivers determining the occurrence of different types of PRB in aquatic environments, and the eco-evolutionary link between bacterial adaptation and the resulting implications for mammalian hosts are poorly known. This thesis examines the impact of nutrients and predation on PRB, as well as the ecological and evolutionary connection between their life in aquatic environments and mammalian hosts. In the first study seven bacterial isolates from the Baltic Sea were investigated for their plasticity of adaptation to predation. The response to predation showed large variation where some bacteria rapidly developed a degree of grazing resistance when exposed to predators. The rapid adaptation observed may result in bacterial communities being resilient or resistant to predation, and thus rapid adaptation may be a structuring force in the food web. With the aim to elucidate the link between occurrence of PRB and environmental conditions, a field study and a laboratory experiment were performed. In both studies three PRB genera were found: Mycobacterium, Pseudomonas and Rickettsia. PRB were found both in oligotrophic and eutrophic waters, indicating that waters of all nutrient states can harbor pathogenic bacteria. However, the ecological strategy of the PRB varied depending on environmental nutrient level and disturbance. Using an advanced bioinformatic analysis, it was shown that ecotypes within the same PRB genus can be linked to specific environmental conditions or the presence of specific protozoa, cyanobacteria or phytoplankton taxa. These environmental conditions or specific plankton taxa could potentially act as indicators for occurrence of PRB. Finally, using four mutants (with specific protein deletions) of the pathogenic and predation resistant Francisella tularensis ssp. holarctica, I found evidence of an eco-evolutionary connection between the bacterium´s life in aquatic and mammalian hosts (aquatic amoeba Acanthamoeba castellanii and a murine macrophage).  To a large extent F. t. holarctica use similar mechanisms to persist predation by protozoa and to resist degradation by mammal macrophages. To summarize I found a link between predation resistant bacteria in aquatic environments and bacteria that are pathogenic to mammals. Further, I showed that different environmental conditions rapidly selects for PRB with either intracellular or extracellular lifestyles. This thesis provides insights regarding environmental conditions and biomarkers that can be used for assessment of aquatic environments at risk for spreading pathogenic bacteria.  

Place, publisher, year, edition, pages
Umeå: Umeå Universitet, 2017. 28 p.
Keyword
Eutrophication, productivity, predation pressure, predation-resistant bacteria, pathogens, Francisella tularensis, adaptation, biomarker, oligotyping
National Category
Ecology
Identifiers
urn:nbn:se:umu:diva-133338 (URN)978-91-7601-684-8 (ISBN)
Public defence
2017-04-28, Lilla Hörsalen, KB3A9, Chemical Biological Center (KBC), Umeå Universitet, Umeå, 12:30 (English)
Opponent
Supervisors
Funder
Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning, 217-2008-1443Swedish Research Council, 60276201Ecosystem dynamics in the Baltic Sea in a changing climate perspective - ECOCHANGE
Note

Medfinansiärer var även: Swedish Ministry of Defence (A4040, A4042, A404215, A404217), Swedish Minestry of Foreign Affairs (A4952), Swedish Civil Contingencies Agency (B4055)

Available from: 2017-04-07 Created: 2017-04-05 Last updated: 2017-05-10Bibliographically approved

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