| (ZimmermanSM1.rtf)
EFFECTS OF VERY HIGH CO2
ATMOSPHERES ON PHOTOSYSTEMS I AND II OF COMMON CYANOBACTERIA
Shawn M. Zimmerman1,
Shannon L. Sullivan1, 2 and David J. Thomas1.
1Science Division, Lyon
College, Batesville, AR 72501, USA.
2Currently at Vanderbilt
University, Interdisciplinary Biomedical Research Program, Nashville, TN
37235, USA.
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 (delta A830 nm) 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. Cyanobacteria that were sensitive to high CO2
environments (e.g., Synechocystis) exhibited 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.) |