Integrative analysis of the salt stress response in cyanobacteria

In many habitats, microorganisms are exposed to high or fluctuating salinities and evolved specific acclimation strategies to thrive in those environments. Euryhaline microorganisms can grow in a broad range of salinities, from low ionic strength like freshwater up to twofold seawater salinities. Here, we analyzed the salt acclimation process of the euryhaline model cyanobacterium Synechocystis sp. PCC 6803 in a multi-omics approach by combining transcriptomic, proteomic and metabolomic analyses. The Overall, the comparison of salt-induced proteome and transcriptome changes revealed a good correleation between the proteome and transcriptome that as most the majority of stably up-regulated proteins also showed elevated mRNA transcript levels. However, a dynamic reorganization of the transcriptome occurred during the first hours after salt shock, which probably also involves the action of small regulatory RNAs acting at the post-transcriptional level. In addition to the rapid and stable steady upregulation of compatible solute biochemistry, a dynamic reorganization of the transcriptome occurred during the first hours after salt shock, which probably involves the action of small regulatory RNAs. Moreover, the coordinated induction of several stress proteins known to be involved in iron and oxidative stress responses as well as of mechano-sensitive channels was observed. Based on these data, an extended salt stimulon can be defined comprising many proteins directly or indirectly related to compatible solute metabolism, ion and water movements as well as a defined set of small regulatory RNAs. Moreover, the massive accumulation of the compatible solute glucosylglycerol had large impact on the overall carbon and nitrogen metabolism. Our comprehensive data set provides the basis for future attempts to engineer cyanobacterial salt tolerance and to search for processes regulating this important environmental acclimation process. We analyzed gene expression in Synechocystis sp. PCC 6803 WT 0.5, 2 and 24 hours after a shift from 0% NaCl to 4% NaCl. For each sampling point, 2 biological replicates were analyzed.