PARENT SESSION
Posters P4C Controling CO₂: Stomates and carbon concentrating mechanisms. Abstracts (631-642)

Inorganic carbon acquisition in Chlamydomonas sp. under acidic conditions (pH 2.7). Elly Spijkerman^*,,

ABSTRACT- After the reunification of Germany, abandoned mine pits from open-cast brown coal mining often became large, deep, lignite mining lakes, acidified as a result of pyrite-oxidation. In one such lake (111) the pH is extremely low (2.6 - 2.8). As a result of the low pH concentrations of dissolved inorganic carbon are low, and only CO₂ is available. Previous experiments conducted with Chlamydomonas sp., an algal species isolated from Lake 111 show that growth rates at CO₂ concentrations typical in surface strata are approximately 50% of the potential growth rates at CO₂ saturation, under light saturated conditions. Experiments showed that Chlamydomonas sp. can only use CO₂ as an inorganic carbon source and has a very high affinity for the uptake of CO₂ that enables maximal photosynthesis at natural air equilibrium conditions. Furthermore, this affinity was largely unaffected by the availability of glucose or aeration with 5% CO₂ in the growth medium. Such behaviour is likely correlated with the constant stress upon the algal cell caused by the low CO₂ environment, selecting out adaptive strategies for living under increased carbon availability. Storage capacity of inorganic carbon after uptake of CO₂ was often low, but could reach high values in cultures that were severely CO₂ limited. These results indicate that Chlamydomonas sp. has a carbon concentrating mechanism (CCM) and is well-adapted to the low CO₂ environment of Lake 111. From the results it seems likely that the enhancement of growth by CO₂ aeration is also caused by some other factor which is presently unknown and it remains unclear if the species is carbon limited in its growth under in situ conditions. Other factors like cell density, light intensity and temperature are currently under investigation.

KEY WORDS: CCM, ecophysiology, Chlamydomonas, acid lake