Growth-phase dependent differential gene expression in Synechocystis sp. strain PCC 6803 and regulation by a group 2 sigma factor.

Cyanobacteria must continually alter their physiological growth state in response to changes in light intensity and their nutritional and physical environment. Under typical laboratory batch growth conditions, cyanobacteria grow exponentially, then transition to a light-limited stage of linear growth before finally reaching a non-growth stationary phase. In this study, we utilized DNA microarrays to profile the expression of genes in the cyanobacterium Synechocystis sp. PCC 6803 to compare exponential and linear growth. We also studied the importance of SigB, a group 2 sigma factor in this cyanobacterium, during the different growth phases. The transcription of approximately 10% of the genes in the wild type were different in the linear, compared to the exponential phase, and our results showed that: (1) many photosynthesis and regulatory genes had lowered transcript levels; (2) individual genes, such as sigH, phrA, and isiA, which encode a group 4 sigma factor, a DNA photolyase, and a Chl-binding protein, respectively, were strongly induced; and, (3) the loss of SigB significantly impacted the differential expression of genes and modulated the changes seen in the wild type in regard to photosynthesis, regulatory and the unknown genes.