Hydroperoxidases in cyanobacteria.

Cyanobacteria are the most primitive, oxygenic photosynthetic organisms. The advent of primordial cyanobacteria marked the decisive point in evolution, because these organisms were (most probably) the first to liberate bulk amounts of oxygen gas into an anoxic biosphere. It seems likely that cyanobacteria were (among) the first to elaborate mechanisms for aerobic respiration, consequently being the only organisms which have accommodated both oxygenic photosynthesis and aerobic respiration within a single prokaryotic cell. It is known that reduced oxygen species (e.g. superoxide and hydrogen peroxide) are byproducts of these types of electron transport chains. So it is assumed that cyanobacteria have developed first strategies of adapting to oxidative stress by developing the corresponding scavenging enzymes (e.g. superoxide dismutases and hydroperoxidases). But hydrogen peroxide scavenging enzymes (hydroperoxidases, namely peroxidases and catalases) in cyanobacteria have not been investigated down to detail so far. It seems likely that one type of peroxidase in these organisms is the most likely ancestor of the hydrogen peroxide-scavenging peroxidases and that catalase activities are exhibited by typical prokaryotic catalase-peroxidases. It is the aim of this project to purify, characterize and finally localize hydrogen peroxide scavenging enzymes (hydroperoxidases) from two unicellular cyanobacterial species Anacystis nidulans (Synechococcus PCC 6301), Synechocystis PCC 6803 and one filamentous species, namely Anabaena variabilis PCC 7937. The present project should help to push forward efforts in establishing cyanobacteria as simple prokaryotic models for studying the interaction of photosynthetic and/or respiratory electron transport and the response hydrogen peroxide scavenging enzymes as a result of endogenously or exogenously induced oxidative stress situations.