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Seasonality and environmental control of freshwater SAR11 (LD12) in a temperate lake (Lake Erken, Sweden)
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
2013 (English)In: Aquatic Microbial Ecology, ISSN 0948-3055, E-ISSN 1616-1564, Vol. 70, no 1, 33-44 p.Article in journal (Refereed) Published
Abstract [en]

THE SAR11 clade is ubiquitous and abundant in planktonic environments. In freshwater lakes, the clade is represented by tribe LD12 which is phylogenetically distinct from the marine SAR11. We studied the ecology of LD12 in a temperate dimictic lake (Lake Erken, Sweden), by analyzing its seasonal dynamics with quantitative PCR, CARD-FISH and 454 pyrosequencing of the 16S rRNA gene. Results showed that LD12 can be as numerous in freshwater bacterioplankton as their marine SAR11 siblings. They exhibited strong seasonality and made up from 1.8 to 40% of the total bacterial 16S rRNA pool (mean 14%) with pronounced peaks in summer and late fall. Except in spring, LD12 was the dominant Alphaproteobacteria, contributing on average 72% of the 16S rRNA within this class. The LD12 population was dominated by a single persistent ribotype, suggesting low local divergence, at least at the phylogenetic resolution accessed with rRNA genes. The relative abundance of LD12 was positively correlated to nutrient concentrations (phosphate, ammonia, nitrate, and silica) and water transparency whereas the relative abundance was lower during periods characterized by high phytoplankton biomass. Based on these observations we propose that LD12 are poor competitors during periods of high phytoplankton productivity and associated release of labile organic compounds, but thrive when availability of inorganic nutrients is high. Similar to the marine SAR11 sibling group, local LD12 populations appear to respond in contrasting ways to nutrient availability in different lakes, pointing to either ecological divergence within the tribe or variations in the interplay between environmental driver variables.

Place, publisher, year, edition, pages
2013. Vol. 70, no 1, 33-44 p.
Keyword [en]
LD12, Freshwater SAR11, Alphaproteobacteria, Seasonal dynamics, Quantitative PCR, 454 Pyrosequencing, CARD-FISH, 16S rRNA
National Category
Natural Sciences
URN: urn:nbn:se:uu:diva-207118DOI: 10.3354/ame01637ISI: 000322999500003OAI: oai:DiVA.org:uu-207118DiVA: diva2:647007
Available from: 2013-09-10 Created: 2013-09-09 Last updated: 2015-04-17Bibliographically approved
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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Heinrich, FriederikeEiler, AlexanderBertilsson, Stefan
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