Exploring transient phytoplankton spring blooms across lakes to understand the significance and control of

temporal patterns in freshwater bacteria

Bertilsson, S., Hornak, K., McMahon, K.D., Simek, K., Pernthaler, J.

Lake Erken Oct 2008International workshop of the dynamic properties of Aquatic Microbial Communities

Microbial Community/PopulationGain Loss

Cryptic ecological drivers-pH

-phototoxicity-temperature

-toxic compounds-particulate matter/surfaces

External inputs-Hydrological inflow -Precipitation-Mixing / Internal re-distribution

Growth & Competition-Electron donors -organic -inorganic-Electron acceptors-Solar radiation-Nutrients -phosphorus -nitrogen -trace elements

Mortality-Microzooplankton grazing-Protozoan grazing-Viral lysis

Export-Hydrological outflow-Sedimentation-Aerosolization

Modified from Shade et al., 2009, The ISME Journal

By concerted high-frequency sampling and analysis of microbial variables, functional traits and driver variables in multiple well-studied freshwater lakes, we will address a number of central questions in aquatic microbial ecology and aquatic ecosystem response to environmental change.

TIMING: What triggers and terminates (clonal) spring blooms of microorganisms across different lakes? When does it happen (relative and absolute timing)? DRIVERS: What is the role of vertical spatial structure (and associated chemistry), solar radiation and predation pressure? Will the trajectory and pace of community change vary among the studied lakes and how does this relate to climatic region and lake size (buffering capacity). INTERACTIONS: Is there synchrony in spring microbial community succession and can contrasting growth strategies be identified among populations (stable/dynamic)? Are there links between individual bacterial populations and phytoplankton

•Bacterial community composition using ARISA – McMahon•Bacterial community composition using barcoded 454 sequencing– Bertilsson•Bacterial community composition by FISH – Pernthaler•Viral counts – Simek•Quantitative assessment of specific group of bacteria:

-Beta-proteobacterial populations Simek-FISH, Reverse Line Blot-Jezbera-Actinobacterial populations McMahon-QPCR, Pernthaler-FISH-Alphaproteobacteria populations SAR11: Bertilsson-QPCR, Pernthaler-FISH-Flavobacteria populations Pernthaler-FISH; Bertilsson-QPCR/T-RFLP

•Bacterial numbers and biomass – All groups•Bacterial production (leucine incorporation)-All groups •Parameters that may vary among sites:

ZooplanktonPhytoplanktonHeterotrophic nanoflagellatesBrdU-FISH probing of replicating bacterial groups

An Array of Microbial Variables(using standardized methods)

temperature (vertically resolved), PAR and precipitation, chlorophyll-a, DOC, absorbance/water color, nutrients (TP, TRP, NH4, NO3, Si) and oxygen

The lakes

Lake Zürich

Ice Stratification

Lake Erken

Lake Mendota...

(the image has nothing to do with the actual UW-CL sampling vessels...)

Water column seasonality in Erken (2008/2009)

Chl a Chl a

AVERAGE LAKE SURFACE WATER BACTERIAL COMMUNITY COMPOSITION (390.000 rRNA sequences for 70 lakewater samples)

Abundance patterns of bacterial populations:-Epilinnetic water samples

Grouped by phylogeny Grouped by abudnace pattern

Correlating bacterial populations to environmental variables

Actino

Bacteroidetes

Cyano

AlphaBeta

GammaVerrucomicrobia

r-value