DepletionofVipp1inSynechocystis sp.PCC6803a¡ects photosynthetic activitybefore the lossofthylakoidmembranes

A vipp1 mutant of Synechocystis sp. PCC 6803 could not be completely segregated under either mixotrophic or heterotrophic conditions. A vipp1 gene with a copperregulated promoter (PpetE-vipp1) was integrated into a neutral platform in the genome of the merodiploid mutant. The copper-induced expression of PpetE-vipp1 allowed a complete segregation of the vipp1 mutant and observation of the phenotype of Synechocystis 6803 with different levels of vesicle-inducing protein in plastids 1 (Vipp1). When PpetE-vipp1 was turned off by copper deprivation, Synechocystis lost Vipp1 and photosynthetic activity almost simultaneously, and at a later stage, thylakoid membranes and cell viability. The photosystem II (PSII)mediated electron transfer was much more rapidly reduced than the PSI-mediated electron transfer. By testing a series of concentrations, we found that PpetE-vipp1 cells grown in medium with 0.025 mM Cu showed no reduction of thylakoid membranes, but greatly reduced photosynthetic activity and viability. These results suggested that in contrast to a previous report, the loss of photosynthetic activity may not have been due to the loss of thylakoid membranes, but may have been caused more directly by the loss of Vipp1 in Synechocystis 6803.