The SigB Sigma Factor of the Cyanobacterium Synechocystis sp. PCC 6803 Is Necessary for Adaptation to High-Salt Stress

The sigma (σ) factors of RNA polymerase are required for transcription initiation. In addition to a primary σ factor, cyanobacteria have several primary-like σ factors that have important roles when bacteria adapt to a changing environment. Salt stress reduces cyanobacterial growth and photosynthesis and results in the expression of chaperones and the synthesis of compatible solutes as a means of defense. We studied salt stress responses in the glucose tolerant control strain of Synechocystis sp. PCC 6803 and in a σ facto inactivation strain, ΔsigB. At the beginning of salt stress the sigB gene is strongly expressed in the control strain. Under salt stress ΔsigB lost more of its PSII capaCity than the control strain. In prolonged salt stress the inactivation strain recovered its PSII capaCity less efficiently than the control strain and grew poorly. Based on these results we concluded that the SigB σ factor of Synechocystis sp. PCC 6803 is crucial for acclimation to salt stress.