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Adaptations of freshwater bacteria to a variable substrate field

English title Adaptations of freshwater bacteria to a variable substrate field
Applicant Pernthaler Jakob
Number 163217
Funding scheme Project funding
Research institution Limnologische Station Universität Zürich
Institution of higher education University of Zurich - ZH
Main discipline Ecology
Start/End 01.10.2015 - 30.09.2018
Approved amount 525'000.00
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All Disciplines (2)

Discipline
Ecology
Hydrology, Limnology, Glaciology

Keywords (7)

freshwater bacterioplankton; metatranscriptomics; single-cell activity; dissolved organic matter; substrate incorporation; habitat heterogeneity; metagenomics

Lay Summary (German)

Lead
Organisches Material in Seen löst sich aus zahllosen Punktquellen, wie z.B. absterbenden Algenzellen, und wird anschliessend durch Diffusion und Turbulenzen im Wasser verteilt. Daraus ergibt sich ein Gefüge an Konzentrationsgradienten, in denen Mikroorganismen sich orientieren müssen, um erfolgreich zu wachsen. Das Projekt untersucht mögliche mikrobielle Wachstums-Strategien, um in einer komplexes "Landschaft" aus unterschiedlich hohen Nährstoffkonzentrationen im Seewasser zu existieren.
Lay summary

Die Wassersäule von Seen erscheint auf den ersten Blick als ein weitgehend unstrukturierter Lebensraum, in dem das gelöste organische Material gleichförmig verteilt ist. In Wirklichkeit stammen jedoch viele der kleinen organischen Moleküle, welche die Nahrungsgrundlage vieler Bakterien bilden, aus punktförmigen Quellen wie absterbende Algenzellen oder anderem partikuläres Material, welches von Mikroorganismen besiedelt wird. Ein Teil der so gelösten organischen Verbindungen wird dabei freigesetzt und durch Turbulenzen in der Wassersäule verteilt. Planktische Bakterien existieren daher in einem Lebensraum von Konzentrationsgradienten. Manche Mikroorganismen können diese nützen, um sich zu orientieren, und durch aktive Beweglichkeit (Geissel) zur Quelle eines bestimmten Substrates zu gelangen. Für diese Bakterien sollte eine erhöhte Substratkonzentration also dazu dienen, Vorhersagen über zukünftige (bessere) Wachstumsbedingungen zu treffen. Erwartungsgemäss sollten sie mit einer umfassenden metabolischen Regulation auf solche Bedingungen reagieren. Andere Bakterien hingegen besitzen keinen Fortbewegungsapparat, und können daher auch keine Substratquellen ansteuern. Dennoch ist zu erwarten, dass sie Anpassungen haben, um die gegebenen Konzentrationsunterschiede optimal auszunützen. Beispielsweise könnten sie die nötige Kapazität für kurzfristig höheren Substrattransport in die Zelle permanent zur Verfügung zu stellen, sodass keine Genregulation erforderlich wäre.

Im ersten Schritt des geplanten Projekts wollen wir die -theoretisch plausible, empirisch weitgehend unbewiesene- räumliche Unterschiedlichkeit des Substratfeldes in einem See am Beispiel der Aminosäuren untersuchen, und zwar auf Skalen von Zentimeter bis Kilometern. Aufgrund dieser Information werden wir anschliessend Experimente mit Substratanreicherungen durchführen, um die Reaktion verschiedener mikrobieller Lebensformtypen mit der erwarteten Vorhersage unseres Modells zu vergleichen.

Direct link to Lay Summary Last update: 07.10.2015

Responsible applicant and co-applicants

Employees

Publications

Publication
Spatiotemporal distribution and microbial assimilation of polyamines in a mesotrophic lakePolyamine variability and bacterial assimilation
Krempaska Natalia, Horňák Karel, Pernthaler Jakob (2018), Spatiotemporal distribution and microbial assimilation of polyamines in a mesotrophic lakePolyamine variability and bacterial assimilation, in Limnology and Oceanography, 63(2), 816-832.
Strain-specific consumption and transformation of alga-derived dissolved organic matter by members of the Limnohabitans -C and Polynucleobacter -B clusters of Betaproteobacteria
Horňák Karel, Kasalický Vojtěch, Šimek Karel, Grossart Hans-Peter (2017), Strain-specific consumption and transformation of alga-derived dissolved organic matter by members of the Limnohabitans -C and Polynucleobacter -B clusters of Betaproteobacteria, in Environmental Microbiology, 19(11), 4519-4535.
High-throughput determination of dissolved free amino acids in unconcentrated freshwater by ion-pairing liquid chromatography and mass spectrometry
Horňák Karel, Schmidheiny Helen, Pernthaler Jakob (2016), High-throughput determination of dissolved free amino acids in unconcentrated freshwater by ion-pairing liquid chromatography and mass spectrometry, in Journal of Chromatography A, 1440, 85-93.

Collaboration

Group / person Country
Types of collaboration
Bas Ibelings, University of Geneva Switzerland (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Research Infrastructure
H.-P. Grossart, Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Berlin, Germany (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
- Exchange of personnel

Scientific events

Active participation

Title Type of contribution Title of article or contribution Date Place Persons involved
ASLO Aquatic Sciences meeting Poster Synchronous changes contrast with different stability of dissolved free amino acid and glucose concentrations in a mesotrophic lake 26.02.2018 Hawaii, United States of America Hornák Karel;
Invited presentation, Université du Québec à Montréal (UQAM) Individual talk Dynamics and microbial turnover of labile organic carbon compounds in a prealpine lake 07.07.2016 Montreal, Canada Pernthaler Jakob;
Invited presentation, Institut of Marine Sciences ICM Individual talk Microbial turnover of labile organic carbon compounds in a prealpine lake 03.05.2016 Barcelona, Spain Pernthaler Jakob;


Associated projects

Number Title Start Funding scheme
141166 Niche partitioning and ecophysiology of lacustrine bacteria that resist protistan grazing 01.08.2012 Project funding
182336 Community assembly processes of ‘opportunistic’ freshwater bacteria 01.10.2018 Project funding

Abstract

Free-living freshwater microbes appear to thrive in an unstructured environment that is largely homogeneous with respect to substrate distribution. However, physical, biogeochemical and biological factors superimpose structure onto pelagic habitats at various spatial and temporal scales. This heterogeneity may be relevant for bacterial assemblages in the productive surface water layers, as it mediates the co-existence of genotypes with contrasting growth strategies. For example, motile and non-motile bacterioplankton populations could have different ecophysiological adaptations to locally variable substrate levels. Motile cells track gradients of organic compounds; they are thus expected to interpret a rise of substrate concentrations as a signal for increasingly favourable growth conditions, and to rapidly undergo general metabolic up-regulation. By contrast, non-motile bacteria are passively exposed to stochastic change of the substrate field from which they cannot predict future growth conditions. They should thus exhibit a much more limited physiological response to substrate heterogeneity. However, also non-motile bacteria should be well-adapted to thrive in a variable substrate field, e.g., by a permanent ‘preparedness’ to rapidly incorporate substrates across concentrations ranges that match environmental fluctuations.Dissolved free amino acids (DFAA) are highly favourable for the growth of many microbial taxa in aquatic systems; thus they are only available at low nanomolar concentrations. Due to the tight coupling between DFAA consumption and release, they qualify as sensitive tracers for exploring the heterogeneous substrate field experienced by free-living aquatic bacteria. DFAA patterns can be determined in less than a millilitre of lake water, allowing for high spatial resolution by appropriate sampling approaches. The proposed project will investigate the extent of substrate variability at the meso- (cm) to macroscale (m, km), and its consequences on the growth patterns of sympatric free-living bacterioplankton populations. We shall chart the heterogeneity of DFAA in Lake Zurich at different spatiotemporal scales and analyse its relatedness to biotic and abiotic factors. This will provide an ecologically meaningful framework for performing pulse addition experiments with DFAA, to test the hypothesis that motile and non-motile bacterial taxa differ in their respective metabolic responses. We shall obtain metagenomic information from these experiments to distinguish between populations with and without genes for motility, and subsequently map metatranscriptomic data onto these populations. In parallel, we will assess motility, compare the substrate uptake velocity of different bacterioplankton taxa, and determine to which extent the transport of DFAA into cells is upregulated by prior exposure.
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