ASGSB 2003 Annual Meeting Abstracts


EFFECTS OF VERY HIGH CO2 ATMOSPHERES ON PHOTOSYSTEMS I AND II OF COMMON CYANOBACTERIA.  Shawn M. Zimmerman, Shannon L. Sullivan and David J. Thomas.  Science Division, Lyon College, Batesville, AR.

   The oxygen in the present-day atmosphere was produced by cyanobacteria and similar organisms 2.5-3.5 billion years ago.  Early photosynthetic organisms evolved in an atmosphere rich in CO2 and poor in O2.  We are currently investigating the tolerance of several cyanobacterial species to very high (>20%) concentrations of atmospheric CO2.  Cultures of Synechococcus, Synechocystis, Plectonema boryanum and Anabaena were grown in liquid culture and bubbled with CO2-enriched air.  Culture growth was monitored by measuring optical density at 750 nm.  Damage to photosystems I and II was monitored by redox-dependent differential absorbance (DA830) and variable fluorescence (FV/FM), respectively.  Synechococcus, Plectonema, and Anabaena tolerated CO2 concentrations up to 100% when the CO2 content was gradually increased from ambient by 10-15% per day. However, Synechocystis did not tolerate high CO2.    Strains that were sensitive to high CO2 were also sensitive to low initial pH (pH 5-6), indicating that the formation of carbonic acid was partially responsible for the inhibited growth in high CO2 environments.  Research in progress indicates that cyanobacteria that are sensitive to high CO2 environments (e.g. Synechocystis) show rapid inhibition of photosystem II as indicated by decreased FV/FM.  The results of photosystem I experiments (in progress) will also be presented.  In addition to providing insight as to the adaptations necessary on the early Earth, this research has applications for Mars exploration (e.g. a martian exploratory base or greenhouse).  Also, this research provides insight into the possibilities, however remote, of forward-contamination of Mars by robotic and human exploration, and the survival of such contaminants. 

(Supported by grants from the Arkansas Space Grant Consortium.)


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