PARENT SESSION
Posters P6C Photosynthesis, respiration and alternative electron sinks. Abstracts (660-680)

Cyanobacteria (blue-green algae) viewed as free-living chloromitochondria. Guenter PESCHEK^*,,

ABSTRACT- Even at a time when no less than 11 completely sequenced cyanobacterial genomes are available (www.kazusa.or.jp/cyano and www.jgi.doe.gov/tempweb/) the bioenergetic situation of this largest, most diversified, evolutionarily most significant, and ecologically most successful group of microorganisms on our earth cannot at all be regarded sufficiently clarified. As of a "free-living chloroplast" the photosynthetic system of a cyanobacterium in the thylakoid membranes (ICM) is extremely well investigated and understood (1). In marked contrast to photosynthesis, the second half of bioenergetic oxygen metabolism, respiration, for the total balance of our biosphere no less important than photosynthesis, still is a miserable black-box in cyanobacteria. The cyanobacterial respiratory chain sits in both ICM and (chlorophyll-free) plasma membranes (CM), in ICM sharing the plastoquinone-plastocyanin/cytochrome-c6 sequence with photosynthesis. In my Vienna research group CM and ICM from 33 different cyanobacteria have been isolated, purified and investigated. All of them contain a complete mitochondria-like respiratory chain, aa3-type cytochrome-c oxidase, and a complete chemiosmotic oxidative phosphorylation system (in the dark) with a (maximum) P/O value of 3 (2); nevertheless, most cyanobacteria are obligate photo(auto)trophs. Here I will briefly summerize our results on cyanobacterial respiration including salient evolutionary and ecological features. LITERATURE: (1) Renger, G., Apparatus and mechanism of photosynthetic oxygen evolution. Photosynth. Res. 76:269-288(2003) (2) Peschek, G.A., Obinger, C., and Paumann,M., The respiratory chain of blue-green algae (cyanobacteria). Physiol. Plant. 120:358-369(2004)

KEY WORDS: Respiration, Evolution, Photosynthesis, Cyanobacteria