Increase in atmospheric CO2 from 280 ppm in pre-industrial time to 386 ppm in present. Expected to rise to 700 ppm by end of century Drop of pH by 0.1, at the ocean surface. Predicted to drop 0.3-0.5 by end of century Current seawater pH 8.0-8.3, HCO3- predominant form of inorganic carbon at 2 mM. CO2 constitutes less than 1% (20 µM) of total DIC. Stichococcus cylindricus Butcher et Umbauk and S. minor Naegeli grown at 20oC in ASW buffered with 50 mM MES at pH 5 and 6; 50 mM HEPES at pH 7, 7.5 and 8.2. Continuous illumination 50 µmol photon m-2s-1 Aeration 28L/h (0.47 L/min) OD measured every 1-3 d at 730 nm Salinity study conducted by varying NaCl (25, 50, 100, 200, & 470mM) * Seawater salinity = 599 mM (35 g/L)

1. PAPER REVIEW
Changes in carbon uptake
mechanisms in two green microalgae
by reduced seawater pH.
NAME : VIJENDREN KRISHNAN
SUPERVISOR : PROF. DR. YOSHIMITSU UEMURA
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3. INTRODUCTION
• Increase in atmospheric CO2 from 280 ppm in pre-industrial
time to 386 ppm in present.
• Expected to rise to 700 ppm by end of century
• Drop of pH by 0.1, at the ocean surface. Predicted to
drop 0.3-0.5 by end of century
• Current seawater pH 8.0-8.3, HCO3
- predominant
form of inorganic carbon at 2 mM.
• CO2 constitutes less than 1% (20 μM) of total DIC.
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4. • Shift the proportion of DIC species to increase CO2
and HCO3
-, while decrease CO3
-2.
• Potentially affect the mode carbon assimilation by
microalgae resulting in changes in primary
productivity, species composition and community
structure.
• Microalgae and cyanobacteria employ a mechanism
that elevate intracellular Ci concentration in the
presence of carbonic anhydase. “CO2 concentrating
mechanism”
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5. Material and Methodology
• Stichococcus cylindricus Butcher et Umbauk and
S. minor Naegeli grown at 20oC in ASW buffered
with 50 mM MES at pH 5 and 6; 50 mM HEPES at
pH 7, 7.5 and 8.2.
• Continuous illumination 50 μmol photon m-2s-1
• Aeration 28L/h (0.47 L/min)
• OD measured every 1-3 d at 730 nm
• Salinity study conducted by varying NaCl (25, 50,
100, 200, & 470mM) * Seawater salinity = 599 mM
(35 g/L)
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6. Result : Growth curve at various pH
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7. Growth curve at various salinity
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8. Rate of O2 evolution and CO2 depletion
of S. cylindricus and S. minor
A
B
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9. Inorganic carbon uptake at
various pH for both microalgae
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10. Inorganic carbon species at
various pH
CO2 + H2O H2CO3 H+ + HCO3
- H+ + CO3
-2
pH 4 ≤ 6.5 pH 6.5 ≤ 10.5 pH 10.5 ≤ 12
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11. CONCLUSION
Decrease in the external pH from 8.2 to 7.5, affected
the mode of inorganic carbon uptake as well as the
growth of both of these Stichococcus species.
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