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The impact of light and water mass on bacterial population dynamics in the Amundsen Sea Polynya
Department of Environmental Microbiology, Helmholtz Centre for Environmental Research – UFZ, Microbial Ecosystem Services Group, Leipzig, Germany. (Department of Ecology and Genetics, Limnology Uppsala University, Uppsala, Sweden)
(Marine Biological Section, University of Copenhagen, Helsingør, Denmark)
(Institute of Marine Sciences, CSIC, Barcelona, Spain)
(Marine Biological Section, University of Copenhagen, Helsingør, Denmark)
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Although the Antarctic Ocean is perpetually cold, mostly ice-covered and dark, it is a highly productive and diverse marine ecosystem. During austral summer, ice-free patches (polynyas) form, exposing marine organisms to sunlight, while mobilizing large amounts of nutrients from the melting ice. As a result, intense phytoplankton blooms form that sustain life across the entire Antarctic food web. This seasonality is likely to shape microbial communities, but the main environmental drivers controlling these communities and the biogeochemical processes they mediate are largely unknown.

In this study, the remote Amundsen Sea Polynya (ASP) was used as a model system to identify the influence of some of the most important environmental drivers of the Southern Ocean. We studied the dynamics in occurrence and activity of abundant members of the bacterioplankton community, directly in environmental samples as well as in microcosm experiments, by using next-generation sequencing of bar-coded 16S rRNA genes in combination with immunochemical detection of DNA-synthesis using bromodeoxyuridine as a tracer.

We found that the photic zone harbored a bacterioplankton community with a low species richness. Here, the dominant populations were related to taxa known to benefit from high organic carbon and nutrient loads (copiotrophs). In contrast, the dark water masses below the photic zone hosted bacterial communities of higher richness, and were dominated by oligotrophs. Results from enrichment studies suggested that indirect impacts of light via photosynthetic production and competition for dissolved nutrients provided in the water masses are the two main factors shaping bacterial communities of the ASP.

Keyword [en]
marine bacterioplankton, population dynamics, Southern Ocean
National Category
Biological Sciences
Research subject
Biology with specialization in Microbiology
Identifiers
URN: urn:nbn:se:uu:diva-229138OAI: oai:DiVA.org:uu-229138DiVA: diva2:735856
Available from: 2014-08-01 Created: 2014-08-01 Last updated: 2014-09-08
In thesis
1. Environmental filtering of bacteria in low productivity habitats
Open this publication in new window or tab >>Environmental filtering of bacteria in low productivity habitats
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Microbes fulfill important ecosystem functions by contributing as drivers of global nutrient cycles. Their distribution patterns are mainly controlled by environmental heterogeneities. So far, little is known about the mode of action of particular environmental drivers on the microbiota, particularly in low productivity habitats.

The aim of this thesis was to investigate the relationships between local environmental drivers and the microbial responses at the level of communities, individuals and realized function, using three structurally different model habitats sharing the feature of overall low productivity. Using a hypothesis-based approach and extensive 16S rRNA amplicon mapping of bacterioplankton colonizing the polar Southern Ocean, I identified how the seasonal formation of open-water polynyas and coupled phytoplankton production affected the diversity of surface bacterial communities and resulted in a cascading effect influencing the underlying dark polar water masses. Additional laboratory experiments, with cultures exposed to light, resulted in reduction in alpha diversity and promoted opportunistic populations with most bacterial populations thriving in the cultures typically reflected the dominants in situ.

Furthermore it was experimentally tested how induced cyclic water table fluctuations shaping environmental heterogeneity in a constructed wetland on temporal scale, by directly affecting redox conditions. Twelve months of water table fluctuations resulted in enhanced microbial biomass, however a shift in community composition did not lead to a significant increase in pollutant removal efficiency when compared to a static control wetland. I detected phyla that have previously been proposed as key players in anaerobic benzene break-down using a protocol that was developed for single cell activity screening using isotope-substrate uptake and microautoradiography combined with taxonomic identification based on fluorescent in situ hybridization targeting the 16S rRNA. Eventually, I provide an example of how anthropogenic pollution with polyaromatic hydrocarbons induced a strong environmental filtering on intrinsic microbial communities in lake sediments.

In conclusion, my studies reveal that microorganisms residing in low productivity habitats are greatly influenced by environmental heterogeneity across both spatial and temporal scales. However, such variation in community composition or overall abundance does not always translate to altered community function.

 

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2014. 44 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1157
Keyword
bacteria, environmental filtering, diversity, ecosystem service, hydrocarbon utilization, Southern Ocean, sediment
National Category
Natural Sciences Biological Sciences
Research subject
Biology with specialization in Microbiology
Identifiers
urn:nbn:se:uu:diva-229144 (URN)978-91-554-8986-1 (ISBN)
Public defence
2014-09-16, Fries salen, Evolutionsbiologiskt centrum, EBC, Norbyvägen 18, 752 36 Uppsala, Uppsala, 10:00 (English)
Opponent
Supervisors
Available from: 2014-08-26 Created: 2014-08-01 Last updated: 2014-09-08

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