Comparative proteomics of cell division mutants and wild-type of Synechococcus sp. strain PCC 7942.

Bacterial cell division is a highly co-ordinated and fine-tuned process. In the unicellular cyanobacterium Synechococcus sp. strain PCC 7942, inactivating mutations in the ftn2 and ftn6 genes block cell division and result in a phenotype with extensively elongated cells. In order to establish the pleiotropic responses induced and cellular processes affected by blocked cell division, the proteomes of wild-type and the cell division mutants Ftn2 and Ftn6 of Synechococcus sp. strain PCC 7942 were characterized and compared. By separating soluble extracted proteins on 2D gels, more than 800 protein spots were visualized on each SYPRO Ruby-stained gel. Quantitative differences in protein composition were detected by using the PDQuest software, and comparative analysis revealed that 76 protein spots changed significantly in the cell division mutants. These protein spots were selected for identification using peptide mass fingerprints generated by MALDI-TOF MS. Fifty-three protein spots were successfully identified, representing 44 different proteins. The upregulated proteins include proteins involved in cell division/cell morphogenesis, protein synthesis and processing, oxidative stress response, amino acid metabolism, nucleotide biosynthesis, and glycolysis, as well as unknown proteins. Among the downregulated proteins are those involved in chromosome segregation, protein processing, photosynthesis, redox regulation, carbon dioxide fixation, nucleotide biosynthesis, the biosynthetic pathway to fatty acids, and energy production. Besides eliciting common responses, inactivation of Ftn2 and Ftn6 in the mutants may result in different responses in protein levels between the mutants. Among 18 identified differentially affected protein spots, 75 % (9/12) of the protein spots affected in the Ftn2 mutant were upshifted, whereas in the Ftn6 mutant 70 % (7/10) of the affected protein spots were downshifted. Identification of such differentially expressed proteins provides new targets for future studies that will allow assessment of their physiological roles and significance in cyanobacterial cell division.