Distributions of aerobic, anoxygenic
phototrophic (AAP) bacteria in the N. Atlantic
Ilana Gilg, Ed Thier, Nicole Poulton, Ralf Goericke
Sieracki et al. 2006. Limnol. Oceanogr. 51:38-46
What are AAP bacteria??
 discovered
to be widespread in ocean by
Kolber et al. 2000
 contain bacteriochlorophyll
 genes found across wide groups of bacteria
 expected to be found in anoxic environments
 photosynthesis does not produce oxygen, uses
alternative reductant source (organic matter?)
“New” ocean bacterial photo-metabolisms
Karl 2002 Nature 415:591
“New” ocean bacterial photo-metabolisms
AAPs
Karl 2002 Nature 415:591
Aerobic Anoxygenic Phototrophs
DAPI - UV
BacChl - IR
Georges
Bank
Sargasso
Sea
Sieracki ME, et al. (2006) Distribution of planktonic aerobic anoxygenic photoheterotrophic bacteria in the
northwest Atlantic. Limnol Oceanogr 51:38-46
Diverse AAP Morphologies
Rods and cocci
Vibrios
Spirilla
Size Spectra
Total bacteria
AAPs
AAPs are larger
than the
average marine
bacteria
Chlorophyll (µg L-1)
0 0.1 0.2 0.3 0.4 0.5
0
5
x 10e3 mL-1
10 15 100 300
500
0
Sargasso Sea
October
Vertical Profile
Microbial
Community
Depth (m)
50
Chl
T
100
Het.
AAPs
150
Bact.
200
250
300
18
20
22
24
Temperature (deg C)
x 10e3 mL-1
0 20 40 60 80 100 0
5
10 15
0
5 10 15 20 25
0
50
100
150
200
250
300
Prochlor.
Synecho.
P. Euks
AAPs are more abundant with higher
chlorophyll and temperatures
120,000
120,000
A
100,000
GB
October
80,000
GB
60,000
40,000
CC
20,000
CC
March
0
0.5
0.5
B
Coastal
80,000
60,000
Sargasso
40,000
20,000
GB
0.00
AAPs /ml
AAPs
AAPs /ml
/mL
100,000
1.0
1.5
1
1.5
22.0
Chl (ug/L)
Chlorophyll (µg/L)
CC
2.5 3 3.0
2.5
0
0 0
55
10
10
15
15
2020 2525 30 30
Temp (°C)(degC)
Temperature
Summary of our AAP results
• AAPs are larger (more biomass per cell) than the
average bacteria
• AAPs have diverse morphologies, especially in the
open ocean
• AAPs are more abundant in productive, coastal waters
than in the open ocean - they correlate with primary
producers
• AAPs are a higher percentage of the total bacterial
biomass in productive, coastal waters (2-12%) than in
the open ocean (2-5%)
AAP Ecology
… SO: AAP cell and biomass distributions do not support the
hypothesis that these cells are specifically adapted to the
low nutrient, open ocean environment
• Analogous to mixotrophic eukaryotes
• Larger AAP cells may be more active, and/or avoid grazing in
open ocean
AAP activity along the Atlantic meridional
transect (AMT16, May-Jun 2005
Koblizek M, Masin M, Ras J, Poulton AJ, Prasil O (2007) Rapid growth rates of aerobic
anoxygenic phototrophs in the ocean. Enviromental Microbiology 9:2401-2406
AAP growth vs. primary production
Koblizek M, Masin M, Ras J, Poulton AJ, Prasil O (2007) Rapid growth rates of aerobic
anoxygenic phototrophs in the ocean. Enviromental Microbiology 9:2401-2406
Photoheterotrophs: potential lightaccelerated carbon shunt in the microbial
food web