The impact of the cyanobacterial carbon‐regulator protein SbtB and of the second messengers cAMP and c‐di‐AMP on CO 2 ‐dependent gene expression

Summary The amount of inorganic carbon (C i ) fluctuates in aquatic environments. Cyanobacteria evolved a C i ‐concentrating mechanism (CCM) that is regulated at different levels. The regulator SbtB binds to the second messengers cAMP or c‐di‐AMP and is involved in acclimation to low C i (LC) in Synechocystis sp. PCC 6803. Here, we investigated the role of SbtB and of associated second messengers at different C i conditions. The transcriptome of wild‐type (WT) Synechocystis and the Δ sbtB mutant were compared with Δ cya1 , a mutant defective in cAMP production, and Δ dacA , a mutant defective in generating c‐di‐AMP. A defined subset of LC‐regulated genes in the WT was already changed in Δ sbtB under high C i (HC) conditions. This response of Δ sbtB correlated with a diminished induction of many CCM‐associated genes after LC shift in this mutant. The Δ cya1 mutant showed less deviation from WT, whereas Δ dacA induced CCM‐associated genes under HC. Metabolome analysis also revealed differences between the strains, whereby Δ sbtB showed slower accumulation of 2‐phosphoglycolate and Δ dacA differences among amino acids compared to WT. Collectively, these results indicate that SbtB regulates a subset of LC acclimation genes while c‐di‐AMP and especially cAMP appear to have a lesser impact on gene expression under different C i availabilities.