Novel adaptive responses revealed by transcription profiling of a Synechocystis sp. PCC 6803 delta-isiA mutant in the presence and absence of hydrogen peroxide.

The isiAB genes have proven to be highly stress-responsive under a variety of environmental conditions, including iron deficiency, high salt and oxidative stress. In order to understand the function of IsiA and its importance in oxidative stress, we constructed a knock out mutant of the isiA gene and compared differential gene expression of the DeltaisiA strain in the presence and absence of H2O2. We used the full genome microarray for the cyanobacterium Synechocystis sp. PCC 6803 as previously described [Postier BL, Wang HL, Singh A, Impson L, Andrews, HL, Klahn J, Li H, Risinger G, Pesta D, Deyholos M, Galbraith DW, Sherman LA and Burnap RL (2003) BMC Genenomics 4: 23-34]. We determined that one of the main differences in DeltaisiA compared to wild-type (in the absence of peroxide) was the induction of a gene cluster (sll1693-sll1696) that encoded genes resembling pilins or general secretory proteins (Gsp). These proteins are targeted to the cytoplasmic membrane and we suggest that they may be involved in the assembly of membrane complexes, including pigment-protein complexes. The DeltaisiA strain was more resistant to H2O2 compared to the wild-type. In the presence of 1.5 mM H2O2 for 30 min, a cluster of genes that includes a peroxiredoxin was induced 7- to 8-fold and we suggest that this peroxide scavenging enzyme is responsible for the increased peroxide resistance of the DeltaisiA strain.