[Construction and evaluation of efficient gene expression platforms in Synechocystis sp. strain PCC6803]

For metabolic engineering of cyanobacteria, there is an urgent need to construct a group of efficient heterologous gene expression platforms and to evaluate their expression efficiencies. Here we constructed three integrative vectors, the pKW1188-derived pFQ9F, pFQ9R and pFQ20, for integration of heterologous genes into the genome of the model cyanobacteria strain Synechocystis sp. strain PCC6803. The pFQ16, an RSF1010-derived broad host range shuttle vector, was constructed for conjugative transfer of genes to various cyanobacteria strains. All the four platforms constructed here applied the rbc (encodes Ribulose-1, 5-bisphosphate carboxylase/oxygenase) and the rbc terminator to promote and terminate the gene transcription. Besides, a "Shine-Dalgarno -AUG" fusion translation strategy was used to keep the high protein translation efficiency. Using lacZ as a reporter gene, the expression efficiency of pFQ20 was evaluated and showed a strong beta-galactosidase expression (109 Miller). Furthermore, the platform pFQ20 was used to express the E. coli tesA' gene and showed significant protein bands through the Western Blot test. The expression platforms constructed in this study offer useful molecular tools for metabolic engineering of cyanobacteria in the future.