This book contains the Proceedings of the Ninth International Symposium on Pho totrophic Prokaryotes (IXth ISPP) which was held in Vienna, Austria, from September 6-12,1997. In 1973, the far-sighted efforts of Gerhart Drews, Roger Y. Stanier, and Nor bert Pfennig launched the first ISPP as a joint forum for scientific discussion of all aspects of research on phototrophic prokaryotes, both anoxygenic and oxygenic (cyanobacteria or blue-green algae). The ISPP International Scientific Committee, a rather loose community of scientists (see page vii for a list of current members), has since been...