biotic controls on microbial communities in estuarine and riverine habitats trisha pascal-lopez...
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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
•Nutrient Input (ex. farm runoff)
•Algal Bloom (consumed by bacteria)
•Bacteria (hypoxia)
•Marine creature die
•Trophic cascade
www.jerrygreerphotography.com/james_river_summer_reflection.htm
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
1) Two different initial environment samples:
• James River mile 21 (Estuarine)
• James River Rice Center (Riverine)
B. Setup
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
i) Environment Phytoplankton Bacteria Grazers
ii) Environment + cycloheximide
Phytoplankton Bacteria -------------
iii) Environment + dark ------------ Bacteria Grazers
iv) Environment + cylcoheximide + dark
------------ Bacteria ------------
2) Four treatments:
• Manipulated light and dark levels
• Eukaryotic growth inhibitor (cycloheximide)
• 3 replicate of each treatment per environment, 3 day incubation
B. Setup
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
Methods
www.compucyte.com/pubbacterialdetection.htm
C. ResultsInitial comparison
• Distinct communities at start of experiment
• Estuary had lower phytoplankton, grazer and bacteria abundance than riverine site (Rice).
EstuaryEstuarysitesite
RiceRiceCenterCenter
Were the treatments effective?
Estuary Rice Center
Ch
loro
ph
yll
(RF
U)
0
2
4
6
8
LightLight + cycloheximide DarkDark + cycloheximide
Estuary Rice Center
Gra
zer
cou
nts
(o
rgan
ism
s/m
l)
0
20
40
60
80
100
120
LightLight + cycloheximideDarkDark + cycloheximide
Estuary Rice Center
Gra
zer
div
ersi
ty (
nu
mb
er o
f ty
pes
)
0
1
2
3
4
5
LightLight + cycloheximideDarkDark + cycloheximide
• Changes to the phytoplankton population (greater for estuary)
• Affected estuary & riverine phytoplankton differently
• Reduced grazer abundance
• Grazers linked to phytoplankton?
• Decrease in grazer diversity
How did bacteria respond to the changes in the phytoplankton and grazer abundance/ diversity?
Estuary Rice Center
Bac
teri
al c
ou
nts
(ce
lls/
ml)
0
2e+6
4e+6
6e+6
8e+6
1e+7
LightLight + cycloheximideDarkDark + cycloheximide
Estuary Rice Center
Cu
ltu
rab
ilit
y o
n s
ite-
spec
ific
med
ia (
%)
0
2
4
6
50
75
100
125
150
LightLight + cycloheximideDarkDark + cycloheximide
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?
Estuary: Community composition similar in all treatments
LightDark
+ cyclohex.Dark
Light+ cyclohex.
River: Changes in bacterial community with each treatment.
LightDark
+ cyclohex.Dark
Light+ cyclohex.
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
Thank You
Questions?