Mechanisms of oxygen evolution in cyanobacteria and its acquisition process(es)

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In order to understand the molecular mechanism of oxygen evolution in cyanobacteria and its acquisition process(es) during the evolution from anoxygenic photosynthetic bacteria to cyanobacteria, we selected one unique species of cyanobacteria, i.e., Gloeobacter violaceus PCC 7421 that lacks thylakoid membranes, a representative example of its primitive characteristics.1.First of all, we determined the complete genome sequence of G.violcaeus by the co-operative research with the Kazusa DNA Research Institute (DNA Res. 10,137,2003). The genome information revealed that this species lacks many genes relating to photosynthesis and other metabolic pathways ; for example, kai A/B/C for circadian rhythm.2.We tried to construct the transformation system of this species, however at the moment, we have not yet succeeded the development of the system. A rigid cell wall may be the cause for incorporation of exogenous gene.3.We directly evaluated the oxygen evolution properties of this species. The steady-state oxygen evolution activity was approximately 250 μmoleO2/mg Chl/hr, a little lower than that estimated on Synechocystis sp.PCC 6803. A typical feature was a very high activity in respiration, approximately 10 times higher than that in Synechocystis sp.PCC 6803. This clearly indicates difference in the electron transfer system in G.violaceus where respiratory and photosynthetic flows are coupled to each other.4.Thermoluminescence, an index of oxygen evolution, was measured on G.violaceus. Its oscillation pattern showed the four-periodic change, as seen in other cyanobacteria, indicating the conserved reaction mechanism of water oxidation, four-step electron transfer.5.As revealed from genome sequence, G.vioalceus is unique in its properties of photosystem II, it seems convincing that transformation of this species will bring about many possible experiments for our understanding on the oxygen evolving system.