Relationship between bacterial community composition and bottom-up versus top-down variables in four eutrophic...

Area of Science:

• Environmental microbiology
• Aquatic ecology
• Limnology

Background:

• Shallow eutrophic lakes exhibit distinct clearwater and turbid states.
• Bacterial community dynamics are influenced by nutrient availability and grazing pressure.
• Understanding these factors is crucial for lake ecosystem management.

Purpose of the Study:

• To investigate seasonal bacterial community composition in shallow eutrophic lakes.
• To determine the influence of bottom-up (resources) and top-down (grazers) factors on bacterial communities.
• To compare the effectiveness of relative band intensities versus presence/absence data in DGGE analysis.

Main Methods:

• Denaturing Gradient Gel Electrophoresis (DGGE) of PCR-amplified prokaryotic rDNA genes.
• Canonical Correspondence Analysis (CCA) to relate community composition to environmental variables.
• Variation partitioning to assess top-down regulation after accounting for bottom-up effects.
• Use of an artificial dataset to validate DGGE analysis methods.

Main Results:

• Bacterial community composition correlated better with environmental variables using relative band intensities than presence/absence data.
• In high-nutrient lakes, bacterial communities were linked to phytoplankton biomass; this link was absent in low-nutrient lakes.
• No top-down regulation of bacterial communities was observed in turbid lakes.
• Grazing by ciliates and daphnids significantly impacted bacterial communities in clearwater lakes.

Conclusions:

• Seasonal bacterial community structure in shallow eutrophic lakes depends on dominant organic matter sources and food web interactions.
• Top-down control is more prevalent in clearwater lakes, while bottom-up control is significant in turbid lakes.
• DGGE analysis using relative band intensities provides robust insights into bacterial community dynamics.