Experimental risk assessment for dispersal,
invasion, and impact on wild algae of
genetically-modified Scenedesmus dimorphus
UCSD
Shovon Mandal
Nathan Schoepp
Jonathan Shurin
Steven Mayfield
Michael Burkart
Ryan Stewart
Steven Villareal
Sapphire Energy
Shawn Szyjka
Yan Poon
Briana Niessen
Synthetic biology to improve algae biofuel feedstocks:
What are the risks to native ecosystems?
Three stages of invasion:
dispersal, establishment, impact
Three stages of invasion:
dispersal, establishment, impact
Three stages of invasion:
dispersal, establishment, impact
Measuring dispersal
Measuring dispersal
A- days to invasion
22%
20%
18%
16%
14%
12%
10%
8%
6%
4%
2%
E
B- percent invaded
20
10
34
0
21
>59 26
42
34
50
40
100
100
0 100
Distance: P=0.0003
100
Distance*direction:
P=0.004
75
75
-10
32
30
(m/s)
Frequency of counts by wind direction (%)
20
30
0 to 1 1 to 2 2 to 3
10
mean = 0.681
S calm = 15.8%
0
0
40
W
distance North (meters)
> 59
-10
distance North (meters)
50
N
-10
0
10
20
30
40
50
distance East (meters)
-10
0
10
20
30
40
50
distance East (meters)
Measuring dispersal
A- days to invasion
22%
20%
18%
16%
14%
12%
10%
8%
6%
4%
2%
E
B- percent invaded
20
10
34
0
21
>59 26
42
34
50
40
30
(m/s)
Frequency of counts by wind direction (%)
20
30
0 to 1 1 to 2 2 to 3
100
10
mean = 0.681
S calm = 15.8%
0
100
0
0
40
W
distance North (meters)
> 59
100
75
75
100
-10
32
-10
distance North (meters)
50
N
-10
0
10
20
30
40
50
distance East (meters)
-10
0
10
20
30
40
50
distance East (meters)
Measuring colonization in native plankton
Population grows in all lakes regardless
of starting density
0.8
0.8
0.6
0.2
10^6
10^5
10^4
10^3
10^6
10^5
10^4
10^3
10^6
10^5
10^4
10^3
Initial density (cells/ml)
0.0
0.2
0.4
0.6
GM
WT
0.0
0.2
0.0
10^6
10^5
10^4
10^3
Santee
0.4
0.6
0.8
Lindo
0.4
0.6
10^6
10^5
10^4
10^3
0.0
0.2
0.4
0.6
0.4
0.2
0.0
r (day-1)
Poway
0.8
Murray
0.8
Miramar
Lake: P<0.001
Density: P<0.001
Lake*density: P=0.01
Measuring impact
• Does invasion affect diversity, composition or
biomass of native algal species?
No effect of GMO on algal biomass
1
8 15
Day
24
1
8 15
Day
24
1
8 15
Day
24
6
Santee
0
1
2
3
4
5
6
5
3
2
1
0
0
1
2
3
4
5
6
Lindo
4
5
4
3
2
1
0
1
2
3
4
5
GM
WT
C
0
Chlorophyll-a (log ug/L)
Poway
6
Murray
6
Miramar
1
10
22
1 10
Day
Lake: P<0.0001
Treatment: P<0.0001
Date: P=0.0003
Lake*treatment: P=0.02
22
Day
Control
WT
GM
Santee
Lindo
Poway
Miramar
Lake: P<0.0001
Lake*treatment: P=0.06
Murray
number of algal species
0 5 10
No effects on native diversity
No effects on native species composition
RDA2
0.5
1.5
Santee
GM
Control WT
-0.5
Lindo
Scenedesmus addition
Miramar
Poway
Murray
-2.0
-1.5
-1.0
-0.5 0.0
RDA1
0.5
Unproductive
lakes
1.0
Conditions for spread of GMO algae
Dispersal
• GM Scenedesmus colonize tanks up to 50m from
raceway
• Dispersal rate declines with distance from source
Conditions for spread of GMO algae
Dispersal
Invasion
• GM and Wild-type Scenedesmus populations grow in
lake water with native plankton communities at any
starting density
Conditions for spread of GMO algae
Dispersal
Invasion
x Impact
• No apparent effects on biomass, diversity or
composition of native algae
What risks do GMO algae pose to native
ecosystems?
• Modified or unmodified algae are likely to
disperse from cultivation and colonize natural
water bodies
• GM Scenedesmus is ecologically
indistinguishable from WT in its impact on
native ecosystems