In regards to our discussion about the possibilities of autotrophic organisms on Mars being dangerous. There was an interesting new report about cyanobacteria, which are photosynthetic therefore autotrophic, being able to "follow the water":

Desert Bacteria Makes Case for Life on Mars
September 28, 2001 07:50 CDT
"Scientists at the Arizona State University have observed and postulated for the first time that bacteria may move with the advance and recession of water rather than sunlight as had been previously believed. "
http://www.cosmiverse.com/space09280101.html

It is interesting that such bacteria are found in duricrusts in the desert on Earth. Such crusts were observed by the Viking landers on Mars and have been found to be wide spread on Mars by the MGS camera:

Global Distribution of Dissected Duricrust on Mars
Mustard, J. F.; Cooper, C. D.
31st Annual Lunar and Planetary Science Conference, March 13-17, 2000, Houston, Texas, abstract no. 1168
http://adsabs.harvard.edu/cgi-bin/bib_query?2000LPI....31.1168M

The cyanobacteria were formerly known as "blue-green algae" and are still sometimes informally referred to that way. It is now known however that they are unrelated to algae.

It is known that there are some toxic forms of cyanobacteria:

The Toxic Cyanobacteria
http://lurac.latrobe.edu.au/~botbml/cyanos.html

Bob Clark