Photosynthesis and hydrogen evolution under stress conditions in a CO2-tolerant marine green alga, Chlorococcum littorale

The influence of the stress factors pH and temperature on photosynthesis and photohydrogen evolution was investigated in a unicellular marine green alga, Chlorococcum litrorale. Maximum activities of photosynthetic oxygen evolution and photohydrogen evolution were determined at 5% CO2, pH 7.5 and 25 degrees C. Increases in pH or temperature caused damage of photosystem II, whereas the photohydrogen-producing system was much less affected. At pH 11, a decrease in photosynthetic oxygen evolution was observed, caused by partial inhibition of the water-splitting complex. This led to photohydrogen evolution lasting for more than 1 h. At high temperatures, both photosynthesis and H-2 evolution became unstable.