Light acclimation of triple inactivation strain of group 2 sigma factors in synechocystis sp. strain PCC 6803

Abstract

The cyanobacterium Synechocystis sp. PCC 6803 encodes nine σ factors, all belonging to the σ70 family. We inactivated three out of the four group 2 σ factors of Synechocystis simultaneously in all possible combinations and found that all triple inactivation strains grow well under standard conditions but show defects in light acclimation. In vivo absorption spectra measurements indicate similar relative absorption of chlorophyll a and phycobilisomes in all strains but high carotenoid content in the ΔsigCDE strain. All triple inactivation strains are characterized by high PSII fluorescence in 77 K emission spectra. The ΔsigBCD, ΔsigBDE, and ΔsigCDE strains showed state 1 transition upon illumination with blue light, but the ΔsigBCE strain was locked to state 1. The strains missing both SigB and SigD factors simultaneously (ΔsigBCD and ΔsigBDE) were not able to grow faster when light was doubled from the PPFD of 40 μmol m−2 s−1 to the PPFD of 80 μmol m−2 s−1. Furthermore, all triple inactivation strains grew slowly in dim light.