Inactivation by gene disruption of 2-cysteine-peroxiredoxin in Synechocystis sp. PCC 6803 leads to increased stress sensitivity

2-Cysteine-peroxiredoxins (2-CP) constitute a ubiquitous group of enzymes w hich reduce toxic alkyl hydroperoxides. In higher plants it was shown that the nuclear encoded 2-CPs are posttranslationally imported into the chlorop lasts; the site of most active oxidative metabolism in plants (Baier and Di etz 1997, Plant J. 12. 179-190). The genome of the bluegreen alga Synechocy stis (EMBL acc. # D64000) encodes a 2-CP which shares 60% homology to highe r plant 2-CPs on the gene level and about 70% on the level of the mature pr otein. In order to elucidate the physiological significance of 2-CPs for ph otosynthetic organisms, the 2-CP gene was mutated in Synechocystis sp. PCC 6803 by insertion of a kanamycin gene cartridge. Following complete segrega tion mutant lines were analyzed for growth and photosynthetic parameters. T he mutants revealed decreased growth rates as compared to the wild type. Gr owth inhibition was relieved after lowering the concentration of Fe or trac e elements in the growth medium. Chlorophyll a fluorescence transients as i nduced by saturating light pulses were used as indicator for the state of p hotosynthesis. The effective quantum yield decreased at lower light intensi ties in the mutants as compared to the wild type Synechocystis. Simultaneou sly, electron transport rates saturated at lower light intensities in the m utants. These data provide the first evidence that 2-CPs play a pivotal pro tective role in photosynthesis.