1. This graph displays the average direction change response times for
Stauroneis phoenicenteron (circles) and Craticula cuspidata cells
(squares) irradiated at their leading end with high irradiance blue light (470
nm; ca. 105
µmol/m2
/s), as a function of the ratio of Stauroneis:Craticula
present in the sample assemblage in which the cells were incubated. The
responses show that the Stauroneis have a dose-dependent increase in
response times as the amount of Craticula in the sample was increased.
The Craticula cells showed no cell-dependent change in response times.
For comparison, un-irradiated Stauroneis and Craticula cells had
response times of 178 ± 10 s and 65 ± 4 s. Error bars represent ± 1 SE.
Analysis of Multiple Species Presence
on Diatom Motility
ABSTRACT #1375
Diatoms, like other algae, ordinarily live within complex multi-species algal communities. Diatoms are crucial
components in these aquatic communities, providing one of the most abundant primary food sources. In order
to help manage the development of healthy aquatic ecosystems it is important to understand the ecological
stimuli that regulate the ability of motile diatoms to successfully migrate through their local assemblages in
order to successfully exploit resources such as light and nutrients. Our lab has shown how several large
single-celled diatom species display characteristic responses to local conditions such as temperature and light.
We have also showed how several of these conditions such as adhesion and directional responses can often
be modified in the presence of other diatom species. We have investigated this further to show that this effect
can be dependent on the relative abundance of diatom species present. For example, when exposed to high
blue light irradiations at their leading tip, Stauroneis cells (S. phoenicenteron) will reverse direction in about
43±4 s. However, in the presence of Craticula cells (C. cuspidata) the direction change increases in a
concentration dependent manner, increasing to 172±39 s when the Craticula:Stauroneis ratio is 10:1 (same
approximate cell density for all experiments). This type of effect can be generated quickly, and appears to be
rapidly reversible. In a separate experiment, Stauroneis cells alone reversed direction upon blue light
irradiation in 34±3 s, but when these cells were exposed to a large number of Craticula cells this response time
increased to 42±2 sec within just a few minutes of exposure. Upon removal from the Craticula cells and rinsing
in fresh medium, the cells returned to their initial response time of 35±3 sec. In both cases the direction change
response of the Craticula cells seems unaffected by the presence of Stauroneis. We are investigating such
species-dependent modulations of motile characteristics to better understand the ways in which species can
affect each other's motility and might be able to undertake resource partitioning within a complex algal
assemblage to gain even more ecological advantage. This work was supported by grants through the DePaul
College of Science and Health, the DePaul University Research Council, and equipment purchased previously
through NSF Grant IBN-9982897.
S.A. Cohn, K. Patterson, A. Wolske
Department of Biological Sciences, DePaul University, Chicago, IL 60614
CONCLUSIONS
Our results show that the effect of irradiations at the ends
of diatoms can be modulated by the presence of other
species. Specifically, our data indicate:
 When Craticula and Stauroneis cells are placed
together in the same culture, the leading end response
time for Craticula cells is unchanged, while the response
time for Stauroneis is increased. (Figure 1)
 Cell-dependent modulation can also be demonstrated
by the addition (and removal) of Craticula cells to a slide
chamber containing Stauroneis. Addition of Craticula
causes an increase in Stauroneis response time, and
removal and rinsing of the Stauroneis restores the
response time. (Figure 2)
 This modulation is also generated by the presence of
Craticula-treated medium. Histogram analysis suggests
that some cells become selectively less responsive.
(Figure 3)
Neither a coverslip pre-treated with Craticula cells, nor
the addition of Craticula cell walls from dead cells causes
the observed increase in cellular response time of
Stauroneis. (Figure 4, 5)
Figure 1. The effect of high irradiance leading end blue
exposures on Craticula and Stauroneis cells as a
function of Stauroneis:Craticula Ratio.
Double Rear
End Irradiation
0
25
50
75
100
125
150
175
200
225
1:0 9:1 4:1 1:1 1:4 1:9 0:1
ResponseTime(s)
Stauroneis:Cra cula Ra o
Stauroneis
Cra cula
Control
Un-Irradiated
0
5
10
15
20
25
30
35
40
45
Stauroneis
(ini al)
w/ Cra cula Add Stauroneis
(washed)
ResponseTime(sec)
Effect of Cra cula Addi on and
Removal
0
20
40
60
80
100
Control Cra cula Solu on
ResponseTime(s)
Effect of Cra cula Treated Medium
0
2
4
6
8
10
12
14
0-20
21-40
41-60
61-80
81-100
101-120
121-140
141-160
161-180
181-200
NumberofCells
Response Time Range
Distribu on of Cell Responses
Diatom Medium
Crat Treated Medium
Figure 2. The effect of the addition of Craticula on
the response time of Stauroneis.
A) Stauroneis phoenicenteron cells were cleaned 2 times
in distilled water, and then allowed to incubate in either
standard diatom medium, or diatom medium taken from
cultures in which Craticula cells have been growing.
Stauroneis cells were then sealed on a glass slide
chamber, and the tips of cells were illuminated on their
leading or trailing end with 1 sec of high energy light
irradiance (ca. 105
µmol/m2
/s) using epi-illumination and
narrow band filters for blue (470 nm) light. Cells were
allowed to change direction and the time between the
irradiation and the direction change was determined.
Error bars represent ± 1 SE.
B) Histogram analysis of the cell responses seen in A.
Response times o Stauroneis cells in normal medium
showed fewer cells at high response times than
Stauroneis cells incubated in Craticula-treated cultures.
Figure 3. The effect of Craticula-treated medium on Stauroneis
response times.
Stauroneis phoenicenteron cells were cleaned and sealed on a glass
slide chamber. The tips of cells were illuminated on their leading or
trailing end with 1 sec of high energy light irradiance (ca. 105
µmol/m2
/s) using epi-illumination and narrow band filters for blue (470
nm) light. Cells were allowed to change direction and the time between
the irradiation and the direction change was determined. Response
times of single species cultures were compared with that of the
samples after the addition of ca. 10:1 ratios of Craticula:Stauroneis
cells. After measuring response times of Stauroneis in the mixed cell
assemblages, the Stauroneis cells were removed from the mixed
culture, and rinsed, and then placed on a new slide chamber and the
sample tested for response time again. Error bars represent ± 1 SE.
A B
Figure 5. The effect of a Craticula
pre-treated coverslip on Stauroneis
response times.
Cleaned glass coverslips were allowed to incubate in
cultures containing actively moving Craticula cells on
them for 3-5 days. Stauroneis phoenicenteron cells
were cleaned and sealed on a glass slide chamber
containing either a cleaned glass coverslip, or the
Craticula pre-treated coverslip. The tips of cells were
illuminated on their leading or trailing end with 1 sec of
high energy light irradiance (ca. 105
µmol/m2
/s) using
epi-illumination and narrow band filters for blue (470
nm) light. Cells were allowed to change direction and
the time between the irradiation and the direction
change was determined. Error bars represent ± 1
SE.
Figure 4. The effect of a cell walls from dead Craticula
on Stauroneis response times.
Samples of Craticula cells were
killed by inoculating cells into
95% ethanol and allowing cells to
incubate for 10 min. Cell walls
from these cells were then
obtained by placing the cells into
a microcentrifuge, sedimenting
the cell walls, then rinsing them in
distilled water, repeating the
sedimentation/rinse three times.
0
10
20
30
40
50
Stauroneis Alone w/ Dead Cells
ResponseTime(s)
Effect of Dead Cra cula Addi on
Stauroneis phoenicenteron cells were cleaned and sealed on a glass slide chamber.
The tips of cells were illuminated on their leading or trailing end with 1 sec of high
energy irradiance (ca. 105
µmol/m2
/s) blue (470 nm) light, and the response time
measured. Stauroneis were then layered with Craticula cell walls from dead cells, and
response times measured again. Error bars represent ± 1 SE.