Untersuchungen zur Struktur und Regulation des Photosyntheseapparates in Cyanobakterien

Abstract

Gloeobacter violaceus (Gloeobacter) is a slow-growing unicellular cyanobacterium. A unique feature of Gloeobacter is the lack of thylakoid membranes. Gloeobacter has been refractory in terms of genetic manipulation. Chapter 1 describes a transformation system for Gloeobacter facilitating its genetic manipulation. The successful transformation system was then utilized in chapter 2. The aim was to study the effect of heterologous vipp1 expression on the membrane structure of Gloeobacter, which lacks Vipp1. Vipp1 appears to be essential in thylakoid formation and shares sequence homology with the bacterial phage shock protein A (PspA). Expression of vipp1 from Anabaena sp. PCC 7120 or an artificial vipphybrid gene led to improved vitality of Gloeobacter. Electron micrographs revealed that the presence of the Vipphybrid or the Vipp1 protein is not sufficient to induce changes in membrane structure. Chapter 3 deals with regulatory aspects of the photosynthetic apparatus of cyanobacteria. In plants and green algae PSII core proteins undergo light dependent phosphorylation. This reversible phosphorylation is absent in cyanobacteria, although the phosphorylation sites are conserved. The stn8 gene of Arabidopsis thaliana, encoding the kinase specifically phosphorylating PSII, was expressed in Synechococcus PCC 7942. STN8 catalyzes the phoshorylation of the D1 protein in Synechococcus as revealed by immunodecoration. The phosphorylation of the D1 protein in Synechococcus led to increased growth rates, higher chlorophyll contents and differences in fluorescence emission spectra at 77K when cells were grown under suboptimal temperature.