Transcript Trisha Pascall

Biotic controls on microbial
communities in estuarine and
riverine habitats
Trisha Pascal-Lopez
Microbial Ecology Lab,
Mentors: Rima Franklin, Ph.D,
and Amy Jenkins
•Nutrient Input (ex. farm runoff)
•Algal Bloom (consumed by bacteria)
•Bacteria (hypoxia)
•Marine creature die
•Trophic cascade
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_reflection.htm
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
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
------------
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)
www.compucyte.com/pubbacterialdetection.htm
3) Grazer community:
• Abundance and diversity (microscopic determination)
• Mainly protozoa, rotifers and larvae
C. Results
Estuary
site
Initial comparison
•
Distinct communities at start of experiment
•
Estuary had lower phytoplankton, grazer and
bacteria abundance than riverine site (Rice).
8
4
2
0
1e+7
bacterial abundance (cells/ml)
Grazers/protozoa (organisms/ml)
250
6
chlorophyll (RFU)
Rice
Center
200
150
100
50
0
initial
8e+6
6e+6
4e+6
2e+6
0
initial
initial
Were the treatments effective?
8
120
Grazer counts (organisms/ml)
Light
Light + cycloheximide
Dark
Dark + cycloheximide
Chlorophyll (RFU)
6
4
2
100
Light
Light + cycloheximide
Dark
Dark + cycloheximide
80
60
40
20
0
Estuary
Rice Center
Grazer diversity (number of types)
5
0
Estuary
Light
Light + cycloheximide
Dark
Dark + cycloheximide
4
3
Rice Center
• Changes to the phytoplankton
population (greater for estuary)
• Affected estuary & riverine
phytoplankton differently
2
• Reduced grazer abundance
• Grazers linked to phytoplankton?
1
• Decrease in grazer diversity
0
Estuary
Rice Center
How did bacteria respond to the changes
in the phytoplankton and grazer abundance/ diversity?
8e+6
150
Light
Light + cycloheximide
Dark
Dark + cycloheximide
Culturability on site-specific media (%)
Bacterial counts (cells/ml)
1e+7
6e+6
4e+6
2e+6
0
Light
Light + cycloheximide
Dark
Dark + cycloheximide
125
100
75
50
6
4
2
0
Estuary
Rice Center
Estuary
Rice Center
Estuary: Bacteria abundance not linked to phytoplankton or grazers
abundances (unaffected in all treatments).
Rice Center (Riverine): Treatments had an effect on bacterial community.
Changes in bacterial community composition?
Light
Light
+ cyclohex.
Dark
Dark
+ cyclohex.
Estuary: Community
composition similar in
all treatments
Light
Light
+ cyclohex.
Dark
Dark
+ cyclohex.
River: Changes in
bacterial community
with each treatment.
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.
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
Questions?
Thank You