Download Bacterial production and the cycling of DOC

Bacterial production and the cycling of DOC
What is bacterial production and how is it measured?
How is bacterial production related to DOC cycling?
What fraction of DOC do bacteria degrade
and where does this DOC come from?
How is recalcitrant DOC degraded?
Reactivity and the cycling of DOC in seawater
Nonreactive DOC
Δ14C = very old
Semi-reactive DOC
Δ14C=modern
Very reactive DOC
Δ14C=DIC
Heterotrophic microbial production ??
0o and 140 oW
Carlson and Ducklow, DSR II v 42; 639-656
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Non-reactive DOM
Semi-reactive DOM
Very reactive DOM
-C-N-
HO
-C-NO
O
-C-NO
-C-NO
O
-C-NO
-C-N-
CH3
CH2 CH2
Humic substances
Non-reactive DOM
Humic substances
Concentration = 40 µM
Inventory = 650 GT C
Δ14C= -400 to -600‰
Annual flux = 0.1 GTC
O
Proteins
Polysaccharides
Biopolymers…
80-90% of cell C-N-P
Semi-reactive DOM
Proteins
Polysaccharides
Biopolymers…
80-90% of cell C-N-P
Free amino acids
Simple sugars
Urea…etc.
10-20% of cell C-N-P
Very reactive DOM
Free amino acids
Simple sugars
Urea…etc.
10-20% of cell C-N-P
25-40 µM
100 nm-1µM (?)
30-50 GT C
0.1- 1 GT C
Δ14C= +70-90‰ (?)
Moderate to large ?
Δ14C= +70-90‰
Large?
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The marine food chain circa 1960s
(when life was simple)
Carbon flow
Nutrient flow
CO2 + Nuts
(N, P, Si)
Phytoplankton
(PP)
grazers
(g)
Grazers
(G)
The marine food web circa 1980
Introduction of the “microbial loop” concept
Carbon flow
Nutrient flow
CO2 + Nuts
(N, P, Si)
Phytoplankton
(PP)
grazers
(g)
Grazers
(G)
DOC
Bacteria
grazers
(g)
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The marine food web circa >1990s
CO2 + Nuts
(N, P, Si)
Carbon flow
Nutrient flow
grazers
(g)
Viruses
Phytoplankton
(PP)
Grazers
(G)
grazers
(g)
DOC
Viruses
Bacteria
grazers
(g)
What is bacterial production?
gross production = total carbon taken up by bacteria, it is used in the
synthesis of new biomass, and includes both the new biomass and
carbon respired during biomass production.
net production = new bacterial biomass over a set period of time.
Bacterial production measurements almost always measure net production.
Gross production = net production + respiration
Gross production is also referred to as bacterial carbon demand (BCD)
and is related to net production through the growth efficiency or fractional
growth yield:
Gross production = (net production) x (growth yield)
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How is bacterial production measured?
1)
Increase in the number of cells over time
2)
3H-adenine
3)
3H-thymidine
4)
3H-leucine
incorporation (DNA synthesis)
incorporation (DNA synthesis)
incorporation (protein synthesis)
All methods measure net production only (!!!) and require empirically
derived conversion factors. Need bacterial growth
efficiencies to determine gross production (BCD)
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Comparison of bacterial and primary production in different ocean basins
BATS DOC (µM C)
Hansell and Carlson
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BATS DOC (µM C)
DO13C
Hansell and Carlson
Production of DOC by phytoplankton in
laboratory culture
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8
Production of DOC during
grazing by macrozooplankton
Viruses in seawater- can be host specific infecting both eukaryotes
and prokaryotes. They cause the cells to burst and release DOM
Large cells are procaryotes about 0.5 µm in diameter labeled with sybergreen.
Small cells are viruses. From Jed Furhman’s lab at USC (furhmanlab.usc.edu)
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DOC dynamics in a simulated algal bloom
Most DOC accumulation occurs after
nutrients are exhausted (bloom crashes)
During early log phase growth DOC is
being respired by bacteria
Two pools of DOC, reactive and nonreactive (timescale of exp!). Are they being
produced by two different classes of
microbes?
Norman et al. L&O
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Production of very reactive and reactive DOC by
phytoplankton and bacteria
CO2
DOCsr
DOCr
O2
Bacterial production is thought to be
fueled by very reactive DOC that has
a residence time in seawater of hour
to days.
DOCsr
Proximate analysis of algal cells
Chlorophyceae
(green algae)
Tetraselmis maculata
Dunaliela salina
Protein
Carbohydrate
Lipid
Ash
72
58
21
33
7
10
(24)
( 8)
Chrysophyceae
(golden brown algae)
Monochrysis lutheri
Syracosphaera carterae
53
70
34
23
13
7
(6)
(37)
Bacillariophyceae
(brown algae, diatoms)
Chaetoceros sp.
Skeletonema costatum
Coscinodiscus sp.
Phaeodactylum tricornutum
68
58
74
49
13
33
16
36
16
10
10
14
(28)
(39)
(57)
( 8)
Dynophyceae
(dinoflagellates)
Amphidinium carteri
Exuriella sp.
35
37
38
44
23
20
(14)
(8)
Average
57
29
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Most POM is protein, and this is probably a large fraction of reactive DOM
Dissolved “free” amino acids have been measured in seawater at 10’s nM
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Measuring the uptake of DFAA using tritiated AA
Seawater
(DFAA)
Measure total DFAA (typically 30-50 nM)
1)
2)
Add 0.1-1 nM tritiated (*) AA
Incubate 1-4 hr
Particulate *AA
count filter count filtrate
count residue
(respired AA)
Ferguson and Sunda; L&O 29(2) 258-274 (1984)
Ferguson and Sunda; L&O 29(2) 258-274 (1984)
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Ferguson and Sunda; L&O 29(2) 258-274 (1984)
Microbiologists view…..
If DFAA are about 20-40 nM (80-160 nM C)in the euphotic zone of the open ocean,
and turnover times are about 0.5-1 per day; then this will support a bacterial carbon
demand of 80-320 nM carbon.
We assume that there are other substrates (glucose, acetic acid, etc.) that are also
metabolized very quickly and contribute to the “very reactive” fraction of DOM.
Very reactive DOC supports most bacterial production in the ocean
But……..
Geochemists view….
Semi-reactive DOC is 25-40 µM carbon, about 100x higher than DFAA. Does semilabile
DOC contribute to bacterial carbon demand? If semi-reactive DOC turns over seasonally
(every few months) this is 100x or so > than measured AA turnover times and it will
support an equal amount of BCD. How do we measure this??
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…the SAR11 clade represents as much as 50% of the total surface community
and 25% of the subeuphotic microbial community…The biogeochemical role
of SAR 11 clade remains uncertain……”
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Selective uptake and utilization of DOM by different groups of bacteria
Determined using tritiated compounds and MICRO-FISH
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Sampling off the
Oregon coast
•
•
•
Shelf
– depths < 60 m
Slope
– depths < 445 m
Offshore
– depths < 2900 m
Krista Longnecker et al, AEM; 2005, 2006; DSR 2006
Krista Longnecker et al, AEM; 2005, 2006; DSR 2006
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Abundance of leucine assimilating
Prokaryotes in the upper 50m of the water
column using MICRO-FISH
Shelf Slope
Basin
Krista Longnecker et al, AEM; 2005, 2006; DSR 2006
Who are the Bacteria?
K. Longnecker, B. F. Sherr and E. B. Sherr (2005). Activity
and phylogenetic diversity of bacterial cells with high and
low nucleic acid content and electron transport system
activity in an upwelling ecosystem. Applied and
Environmental Microbiology. 71(12):7737-7749.
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Production of “semi”-reactive DOC by phytoplankton in culture
Is the composition of accumulating DOC similar to DOC in seawater?
Do phytoplankton produce semi-reactive DOC?
1HNMR
of seawater
After filtration
In culture, phytoplankton release a
large amount of DOC. The composition
of this DOC does not look like DOC in
seawater however (left). After bacterial
degradation, labile DOC is removed leaving
the semi-labile material behind.
After 37 day of degradation
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The effect of bacterial community structure on DOM degradation
Each year DOC is produced in the surface water during the spring/summer
and exported into the mesopelagic ocean, where it is degraded. Why is it
Degraded in the mesopelagic ocean?
Surface seawater
Deep seawater
Surface bacteria
Deep bacteria
Measure DOC degradation and bacterial growth
The effect of bacterial community structure on DOM degradation
0.3
70
70
65
65
60
60
55
55
Cell C (µmol/L)
0.25
0.2
Surface water/surface inoculum
0.15
0.1
0.05
Deep water/deep inoculum
0
50
1
2
3
4
5
6
7
8
9 10 11 12
0.3
1
Surface/surface
50
1
Deep/deep
70
Cell C (µmol/L)
0.25
In situ
65
0.2
0 days
0.15
60
7 days
0.1
55
0.05
37 days
Surface water/deep inoculum
50
0
1 2 3 4 5 6 7 8 9 10 11 12
Day
1
Surface/deep
Carlson et al. L&O 2004
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DOC (µM)
What is the degradation stoichiometry of recalcitrant DOC ?
180
150
120
90
60
30
0
C/N = 10
0
2
4
6
8
10
12
DON (µM)
Hopkinson and Vallino 2005 (Nature)
13CNMR
spectra of HMWDOM
15N-
and 13CNMR analyses of HMWDOM suggests it is a mixture of amino (C:N=6:1)
and neutral (C:N = 6:0) sugars. If these are degraded in a 1:1 ratio, then C:N of
degraded carbon is 12:1, near the observed value.
Sargasso Sea
3m
NPSG
3m
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Summary
DOC serves as the substrate for heterotrophic bacterial production in the ocean.
Bacterial (net) production (BP) is measured through the uptake of tritiated substrates
or from changes in bacterial cell numbers- large uncertainties (10x) in BP, BCD, GE.
On average BP = 15-20% of PP, or about 10-15 GT C yr-1. At least this amount
of carbon must be processed through the microbial loop.
BP measurements are intimately coupled to protein synthesis, and it is believed that
BP production is fueled through the uptake of very reactive DOM (free amino acids,
peptides, small sugars, urea, etc.).
Very reactive DOM is introduced into the water column via direct release,grazing,
viral lysis, etc.
The role of semi-reactive DOM in BP production is not clear. We still don’t know
How quickly it is cycled, how it impacts bacterial diversity, or how it is degraded.
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