Acute cadmium toxicity and post-stress recovery: Insights into coordinated and integrated response/recovery strategies of Anabaena sp. PCC 7120.

Cyanobacteria, the first photoautotrophs have remarkable adaptive capabilities against most abiotic stresses, including Cd. A model cyanobacterium, Anabaena sp. PCC 7120 has been commonly used to understand cyanobacterial plasticity under different environmental stresses. However, very few studies have focused on the acute Cd toxicity. In this context, Anabaena was subjected to 100 μM Cd for 48 h (acute Cd stress, ACdS) and then transferred into the fresh medium for post-stress recovery (PSR). We further investigated the dynamics of morpho-ultrastructure, physiology, cytosolic proteome, thylakoidal complexes, chelators, and transporters after ACdS, as well as during early (ER), mid (MR), and late (LR) phases of PSR. The findings revealed that ACdS induced intracellular Cd accumulation and ROS production, altered morpho-ultrastructure, reduced photosynthetic pigments, and affected the structural organization of PSII, which subsequently hindered photosynthetic efficiency. Anabaena responded to ACdS and recovered during PSR by reprogramming the expression pattern of proteins/genes involved in cellular defense and repair; CO access, Calvin-Benson cycle, glycolysis, and pentose phosphate pathway; protein biosynthesis, folding, and degradation; regulatory functions; PSI-based cyclic electron flow; Cd chelation; and efflux. These modulations occurred in an integrated and coordinated manner that facilitated Anabaena to detoxify Cd and repair ACdS-induced cellular damage.