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
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
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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