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Rapid adaptation of predation resistance in bacteria isolated from a seawater microcosm
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
Umeå University, Faculty of Science and Technology, Department of Mathematics and Mathematical Statistics. (Arcum)
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. (Arcum)
2016 (English)In: Aquatic Microbial Ecology, ISSN 0948-3055, E-ISSN 1616-1564, Vol. 78, no 2, 81-92 p.Article in journal (Refereed) Published
Abstract [en]

Bacterial defense against protozoan grazing has been shown to occur in many different bacteria. Predation resistance traits may however be plastic, making bacterial com munities resilient or resistant to predation perturbations. We studied the adaptation of pre dation resistance traits in bacteria isolated from a microcosm experiment. In the initial microcosm ex periment the predation pressure on bacteria varied markedly, while changes in the bacterial community composition could not be verified. Seven bacteria were isolated from the microcosm (Micrococcus sp., Rhodobacter sp., Paracoccus sp., Shewanella sp., Rhizobium sp. and 2 un identified species) and these were repeatedly exposed to high predation by the ciliate Tetrahymena pyriformis. High variations in edibility and rate of adaptation of predation resistance traits were observed among the strains. The initial mortality rate of the different bacterial taxa and the change over time varied by a factor of 7 and 24, respectively. Rhodobacter sp. was already predation resistant at the start of the experiment and did not change much over time, while Micrococcus sp., Paracoccus sp. and Shewanella sp. initially were relatively edible and later developed predation resistance. In conclusion, we show that rapid adaptation of predation resistance traits is common among bacteria in an aquatic microbial community, and that a single test of a bacterium’s edibility will in many cases not be enough to fully understand its ecological role, as it will not reveal the potential adaptive response. The results suggest the potential of rapid changes of predation resistance as a mechanism for bacterial communities to be resilient to variations in predation disturbances.

Place, publisher, year, edition, pages
2016. Vol. 78, no 2, 81-92 p.
Keyword [en]
Bacterial isolates, Predation pressure, Predation resistance, Inedible, Adaptation, Tetrahymena
National Category
Ecology
Identifiers
URN: urn:nbn:se:umu:diva-131263DOI: 10.3354/ame01802ISI: 000394504400002OAI: oai:DiVA.org:umu-131263DiVA: diva2:1073316
Available from: 2017-02-10 Created: 2017-02-10 Last updated: 2017-04-06Bibliographically approved
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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Mathisen, PeterSjöstedt de Luna, SaraAndersson, Agneta
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