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Alteration of lake bacterioplankton diversity and community composition during lake stratification and gradual oxygen depletion
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Hypolimnetic waters of many stratifying lakes experience gradual oxygen depletion and seasonal hypoxia as organic matter is degraded with oxygen as terminal electron acceptor. Such changes are known to have dramatic effects on larger organisms, but also resident microbiota are likely to be affected by altered availability of oxygen, nutrients and other chemical constituents. We explored how such seasonal shifts in water mass characteristics influenced the resident bacterioplankton in a mesotrophic temperate lake by tracing the temporal dynamics of bacterial communities and populations at different phylogenetic resolution across the entire period of summer stratification. Compared to the epilimnion, bacterial richness was significantly higher in the hypolimnion where varying hypoxia was also reflected in higher beta diversity. Many abundant groups of freshwater bacteria, such as Actinobacteria acI, Polynucleobacter and freshwater SAR11 (LD12), were abundant in both the epi- and hypolimnion, with distinct temporal and vertical population shifts observed at the 97% population identity level. The mechanisms that lead to closely related populations partitioning into ecotypes are not well understood, but are probably due to fine-tuned physiological adaptions towards oxygen and nutrient concentrations in the lake. The existence of ecotypes partitioned by oxygen availability and the seasonal succession in hypolimnetic bacteria driven by gradual oxygen depletion and associated changes in water chemistry merits further studies on their implications for biogeochemical cycles.

Keyword [en]
hypolimnion, Bacteria, Community Composition, Diversity, Hypoxia, Dynamics, Indicator, Habitat
National Category
Research subject
Biology with specialization in Evolutionary Genetics; Biology with specialization in Limnology
URN: urn:nbn:se:uu:diva-245068OAI: oai:DiVA.org:uu-245068DiVA: diva2:790351
Available from: 2015-02-24 Created: 2015-02-24 Last updated: 2015-04-17
In thesis
1. Drivers of Population Dynamics in Bacterioplankton: Spotlight on Alphaproteobacteria and its dominant SAR11 Lineage
Open this publication in new window or tab >>Drivers of Population Dynamics in Bacterioplankton: Spotlight on Alphaproteobacteria and its dominant SAR11 Lineage
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Bacteria are mediators of biogeochemical cycles and are in this way vital for maintaining life on earth. Their distribution, abundance and functioning are driven by environmental heterogeneity and dynamic change in abiotic and biotic factors. Both, freshwater lakes and oceans play central roles in the global carbon cycle and bacteria in these systems perform many services for the ecosystems, such as the transfer of organic carbon from primary producers to higher trophic levels. With estimated relative abundances up to 50% of the total bacterioplankton, the Alphaproteobacteria lineage SAR11 is the most abundant group of aquatic bacteria. It is globally distributed and can be partitioned into multiple sub-clades, one of which is exclusive to freshwaters. Until recently, the distribution, abundance and ecological role of this freshwater SAR11 named LD12 was unknown. The aim of the thesis was to study the drivers and mechanisms that influence the dynamics of aquatic bacterial communities in general and the SAR11 and LD12 groups in particular. The thesis consists of environmental surveys of a mesotrophic Lake Erken and the western Southern Ocean, an experiment and a data-mining exercise to reveal the phylogenetic structure of the SAR11 lineage on various temporal and spatial scales. The analysis of a long-term bacterioplankton community survey in lake Erken provided insights about the dynamics of the entire bacterial community and the LD12 population over an annual cycle. The results demonstrate that LD12 can be an equally abundant member of freshwater communities as marine SAR11 in oceans. LD12 featured strong seasonality and was positively coupled to environmental conditions indicative for an oligotrophic lifestyle. LD12 as well as other dominant lake bacterioplankton also maintained stable populations throughout spatial and temporal varying environments, but at high phylogenetic resolution, habitat preferences were revealed, particularly in response to oxygen concentrations. The later was not the case in LD12 as a single ribotype dominated. This is in stark contrast to the habitat partitioning with light availability, depth and water masses observed for marine SAR11 subclades in the Southern Ocean. The global data-mining corroborated that LD12 as a group was much less diverse than SAR11 furthermore, suggesting that the marine-freshwater barrier acted as a population bottleneck. My work shows that bacterial populations can respond in very different ways to environmental drivers, highlight the importance of highly resolved temporal and spatial scales as well as the need for high phylogenetic resolutions to target ecologically coherent populations.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2015. 54 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1230
bacterial community dynamics, Alphaproteobacteria, SAR11, LD12, Southern Ocean, lakes
National Category
Research subject
Biology with specialization in Limnology
urn:nbn:se:uu:diva-245072 (URN)978-91-554-9172-7 (ISBN)
Public defence
2015-04-10, Fries-salen, Evolutionsbiologiskt Centrum (EBC), Norbyvägen 14, Uppsala, 10:00 (English)
Available from: 2015-03-19 Created: 2015-02-24 Last updated: 2015-04-17

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