Analysis of stress responses in the cyanobacterial strains Synechococcus sp. PCC 7942, Synechocystis sp. PCC 6803, and Synechococcus sp. PCC 7418:: Osmolyte accumulation and stress protein synthesis

The influence of salt, hear and light shock treatments on physiological processes was compared in the cyanobacteria Synechococcus sp. PCC 7942, Synechocystis sp. PCC 6803, and Synechococcus sp. PCC 7418, which differ regarding their salt tolerance. The accumulation of the osmolytes sucrose and glucosylglycerol started after salt shocks without a lag in the strains 7942 and 6803. In strain 7418 the synthesis of glycine-betaine showed a lag phase of several hours. During this time glucosylglycerol and proline were accumulated. Light shocks led in all strains to the highest reduction of carbon fixation rate followed by salt shock, while heat shocks decreased it only slightly in the strains 6803 and 7418. Protein synthesis rates measured S-35-methionine incorporation were reduced after a salt shock, remained almost unchanged in light- as shocked cells and increased after heat shocks. Comparisons of protein synthesis patterns showed that most of the detected stress proteins seem to be strain-specific and belong to the group of general stress proteins, since they were induced under heat, salt and light stress treatments, respectively. Furthermore, some proteins specific for salt and heat stress were also found. Among the general stress proteins the chaperone DnaK was identified using cross reactions with a specific antibody.