Seasonal changes in microbial
diversity and processes in the
Southern Ocean
Alison E Murray
Bacterioplankton play critical roles in
C-N-S-P-Fe cycling
Carbon Cycle
Sulfur Cycle
Iron Cycle
Nitrogen Cycle
Phosphorus Cycle
Questions
• 1. Seasonal turnover of picoplankton
• 2. Winter picoplankton processes
• 3. Sea ice connections to upper
ocean 1° and 2° productivity
• 4. Changes in remineralization as a
result of climate change
Questions1
• Previous results from coastal Antarctic
Peninsula studies have indicated
substantial turnover of picoplankton
groups (species/ribotypes) over the
seasonal cycle – (i) Is this a pervasive
feature of the southern ocean? (ii)
What are the drivers of these shifts?
and (iii) Are they important to
understanding of Southern Ocean
biogeochemical function?
Seasonal variation: Picoplankton
composition varies significantly
2001-02
1996-97
Bacterial
community
structure:
DGGE
As FISH-stained
cells
Archaeal
abundance
As RNA
Murray et al. 1998, Appl. Environ. Microbiol.
Murray and Grzymski, 2007 Phil. Trans. Roy. Soc. Lond. B;
Church et al. Limnology and Oceanography, 2003
Winter-Archaea
a
Winter Summer
Bact.
Bact.
Seasonal differences in rRNA gene
sequences between summer and
winter (Coastal Antarctic Peninsula
28
clusters
Approx. 18-38% of the winter plankton are chemolithoautotrophs
Conserved gene comparisons (COGs)
Summer vs. Winter:
Summer: Feb
Archaeal
COGS
•Heme degredation/utilization
•Iron utilization protein
•Siderophore interacting protein
•Ferritin
•Fe Transport
•Polyphosphate kinase
360
•Phosphonate utilization
•ABC phosphate transport
•PTS System
•Pullulanase
•1,4 glycosidases
•Xylosidases
1680
•Glycogen utilization
•Trehalose utilization
Winter: Aug
•Siderophore transport
& biosynthesis
•Bacterioferritin
•High-affinity Fe 2+
permease
• Nitrate & nitrite
reductase
584 • Phosphate
transporter,
regulators, porins
•Nitrate/nitrite
transporters
•Nitric oxide
reductase
transporters
•RuBisCO ***
•Bifunctional
dissimilatory
sulfite reductase
Picoeukaryotes dominate late winter
chlorophyll signal
Chlorophyll a mg per L
Picoeukaryote cells per mL
AMLR Study Area
Questions 2
• Gaps in biological process data from
polar winter are pervasive; (i) are
“we” missing important
processes?[chemolithoautotrophy,
mixotrophy, low light adapted
phototrophy?] (ii) By understanding
winter processes (primary and
secondary production & mixotrophy)
can we improve the understanding
of winter biogeochemical cycling?
Further, how do these relate to
processes in the mesopelagic
Gaps in winter microbial studies
WAP: LTER Stn. B 2002-2009
Ducklow et al. 2011 AME
Ross Sea 1996-1997
mMol C m-2 d-1
Ducklow et al. 2001 DSRII
Dark carbon fixation
-1
-1
pMC day
Chlorophyll a μg L
4e+5
0.30
0.24
3e+5
0.18
2e+5
0.12
1e+5
0.06
0
0.00
40
DOC & NO2+3-2 μM
200
BP
DCF
160
120
30
20
80
10
40
0
0
50
2.6
-2
NO2+3
45
2.4
DOC
PO4-2
40
2.2
35
2.0
30
1.8
25
20
1.6
200 210 220 230 240 250 260
Julian Day
-2
Bacterial
cells
Chla
PO4 μM
5e+5
Biomass production
nMC day-1
Bacterial cells mL
-1
Coastal WAP Winter Time Series (IPY)
8e+5
6e+5
+
NH4 additions
4e+5
2e+5
16
12
8
4
0
500
300
400
300
200
200
100
100
0
32
30
PO4-2 μM
NO2+3 μM
Early August
rate
No additions
SO3-2 & S2O3-2 additions
μ13C POC (>0.22 μm) Biomass production
-1
μM C day
1e+6
Dark carbon fixation
pMC day-1
Bacterial cells mL-1
Inorganic additions to seawater incubations
(10 day): dark carbon fixation is stimulated by
N and S additions
28
26
24
22
244 246 248 250 252 254 256
Julian Day
0
2.1
2.0
1.9
1.8
1.7
1.6
1.5
244 246 248 250 252 254 256
Julian Day
Chemolithoautotrophic RuBisCO is abundant
and expressed in Antarctic winter samples – and
NOT in summer
12000
Copy Number
• Assay
environmental
samples collected
in the IPY
• 6 summer (1 site)
• 20 winter (3 sites)
Stn B DNA
10000
Stn B cDNA
8000
Stn SI cDNA
6000
Offshore Stations cDNA
Stn SI DNA
Offshore Stations DNA
4000
2000
0
Feb
Apr
Jun
Date (2008)
Aug
Oct
Metaproteome comparisons support
seasonal differences
Williams et al. 2012 ISMEJ 6:1883-1900
Conceptual model for ecosystem
differences between summer and winter
Dark CO2 fixation
estimated at 0.05
Gt Carbon in
upper 100 m of
the water carbon
(Grzymski et al.2012 ISMEJ
& Manganelli et al. 2009
PlosOne)
Grzymski et al. 2012 ISMEJ
Questions 3
• Sea ice is a key habitat for diatom
growth, and microbial cycling of
organic matter; (i) How do changes
in sea ice (timing of formation…
thickness etc.) influence
picoplankton-driven biogeochemical
cycling?
Changes in ice season annual duration
Sea ice cover derived from scanning multichannel microwave radiometer – Special Sensor
Microwave/Imager (SMMR/SSM/I); Ducklow et al. 2013 Oceanogr.
…changes in sea ice cascade through
the ecosystem – including the microbes.
14 yr. study at Ryder
Bay, Rothera:
Venables et al. 2013
Sea ice
Stratification Phytoplankton & PP
Bacterial production
Ducklow et al. 2012 J. Mar. Sys.
Sea ice roles in micronutrient, DOC and
microbial seeding??
• Strengthen research on establishing understand of trophic
connections between ice-associated and underlying algae
and bacteria (when and where does coupling occur?)
• How will changes in sea-ice associated DOC and POC
influence the microbial loop?
Sea ice
Stratification Phytoplankton & PP Bacterial production
Questions 4
• The mesopelagic and possibly
bathypelagic zones of the Southern
Ocean are major zones of carbon
remineralization;
• (i) how will shifts in stratification and
nutrient distributions with global
warming influence respiratory
processes?
• (ii) given the abundance of
chemolithoautotrophic plankton below
the oxycline, what is their influence on
carbon cycling?
• (iii) how will changes in POC (e.g.
diatoms to smaller cells) influence
remineralization processes?
Microbes and activities in the deep
• High bacterial biomass and
protein production rates were
observed at depth in iceberg alley
• Transmissivity increased at depth
Microbes and associated
detrital material in the
sediment trap
A. Bacterial cells are on average
much larger than those suspended
in the water column
B. Protein production rates are high in
LST samples
LST EEA
167.9
Seawater (average) 23.7±18.8
SEEx (average)
62.7±56.6
1003.4
226.3
18.7±12.5 25.2±12.6
28.7±14.7
Alkaline phosphatase
(raw fluorescence)
N-acetylglucoasmine
(raw fluorescence)
C. Particulate (LST) ectoenzyme
activities are 3-35X higher than
seawater and seawater culture rates
B-glucosidase
(raw fluorescence)
36.32
167.32
42.64
2.83
Aminopeptidase
(raw fluorescence)
IB03-071_LST_C-18-1
IB03-095_LST_C18-2
IB03-168_LST_REF
IB03-096_LST_10nm
pM leucine x hr-1
Sample origin
LST Deployment
4812
257.7±169.0
Recommended Field
Studies
• Incorporate microbial process studies
that look at light and dark carbon
fixation, in addition tor recycling of
carbon in the mesopelagic
• Expand genomic and proteomic
studies in ocean realms, and use this
information and develop sensitive
assays that can be used as indicators
of biogeochemical processes and to
augment models
• Advance the understanding of sea ice
and links between ice-associated
processes and underlying waters (micro
and macronutrients & and trophic
interactions)
• Quantify the relationships between
respiration and carbon export
(coastal/open ocean/sea ice/areas of
upwelling/mixing)
Acknowledgements
WAP Bacterioplankton IPY Team
• Hugh Ducklow, Matt Erickson, Kristen Myers – MBL,
Woods Hole
• Jeff Ghiglione, LOMIC, Banyuls-Sur-Mer
• Carol Arnosti and Sherrif Ghobrial, UNC
• Joe Grzymski, Christian Riesenfeld and Vivian Peng – DRI
Logistic and data support from:
Raytheon Polar Sciences Company, Palmer LTER