Biotic controls on microbial communities in estuarine and riverine habitats

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Biotic controls on microbial communities in
estuarine and riverine habitats
Trisha Pascal-Lopez Microbial Ecology
Lab, Mentors Rima Franklin, Ph.D, and Amy
Jenkins
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• Nutrient Input (ex. farm runoff)
• Algal Bloom (consumed by bacteria)
• Bacteria (hypoxia)
• Marine creature die
• Trophic cascade

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A. Purpose

• Study the ecological relationships that occur in
  an aquatic microbial food web
• To understand the interdependence of three levels
  of the food web (phytoplankton, bacteria, and
  grazers)
• Focus on response of bacteria to other community
  members

www.jerrygreerphotography.com/james_river_summer_r
eflection.htm
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B. Setup

• 1) Two different initial environment samples
• James River mile 21 (Estuarine)
• James River Rice Center (Riverine)

Temp (C) Salinity (ppt) Turbidity (NTU) pH DO (mg/L)
Estuarine site (RM 21) 26.6 16.5 10.5 8.1 8.1
Rice Center (RM 75) 27.2 0.2 15.2 7.9 8.9
Courtesy of Paul Bukaveckas River Ecology lab
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B. Setup

• 2) Four treatments
• Manipulated light and dark levels
• Eukaryotic growth inhibitor (cycloheximide)
• 3 replicate of each treatment per environment, 3
  day incubation

i) Environment Phytoplankton Bacteria Grazers
ii) Environment cycloheximide Phytoplankton Bacteria -------------
iii) Environment dark ------------ Bacteria Grazers
iv) Environment cylcoheximide dark ------------ Bacteria ------------
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Methods

• 1) Phytoplankton community
• Fluorescence detection of chlorophyll levels
• 2) Bacterial community
• Abundance (microscopic direct counts)
• Culturability (counts of solid media/agar)
• Genetic profiling (RAPD DNA fingerprints)
• 3) Grazer community
• Abundance and diversity (microscopic
  determination)
• Mainly protozoa, rotifers and larvae

www.compucyte.com/pubbacterialdetection.htm
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C. Results
Estuary site

• Initial comparison
• Distinct communities at start of experiment
• Estuary had lower phytoplankton, grazer and
  bacteria abundance than riverine site (Rice).

Rice Center
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Were the treatments effective?

• Changes to the phytoplankton population (greater
  for estuary)
• Affected estuary riverine phytoplankton
  differently
• Reduced grazer abundance
• Grazers linked to phytoplankton?
• Decrease in grazer diversity

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How did bacteria respond to the changes in the
phytoplankton and grazer abundance/ diversity?
Estuary Bacteria abundance not linked to
phytoplankton or grazers abundances (unaffected
in all treatments). Rice Center (Riverine)
Treatments had an effect on bacterial community.
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Changes in bacterial community composition?
Estuary Community composition similar in all
treatments
River Changes in bacterial community with each
treatment.
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Implications

• Microbial communities in the Estuarine and
  Riverine environments are different.
• Estuarine environment bacterial communities are
  not linked to grazer or phytoplankton abundance
• Riverine environment shows bacterial interactions
  with phytoplankton and grazer communities
• Microbial community interactions vary depending
  on the environment which controls their response
  to environmental stress.

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D. Future Goals

• Statistical analysis of data
• Chemistry (Nitrogen and DOC)
• Run the experiment again with changes
• Add another mile marker
• Collect water sample at different seasons or
  times of day
• Manipulate nutrient concentration

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Questions?
Thank You