Exploring the comprehensive ROS defense toolbox of selected marine cyanobacteria under hydrogen peroxide stress

The present study elucidates the oxidative stress response mechanisms of two marine cyanobacterial species, Phormidium sp. JMC111 and Microcoleus acutissimus, when exposed to hydrogen peroxide (H₂O₂). Both species tolerated short-term H₂O₂ stress up to 60 min, exhibiting significant biochemical and enzymatic adaptations. Statistical analysis revealed a steady decline in chlorophyll content and degradation efficiency over time, with M. acutissimus maintaining higher resilience compared to Phormidium sp. JMC111. Non-enzymatic antioxidants such as carotenoids, β-carotene, tocopherol, and astaxanthin remained elevated, suggesting a strong photoprotective and radical-scavenging defense, while ascorbic acid and phycobiliproteins declined under prolonged stress. Two-way ANOVA confirmed significant time- and species-dependent variations (p < 0.05) in antioxidant responses. Enzymatic assays on native PAGE revealed distinct isoform patterns of SOD, CAT, POD, and GPx, with the appearance of novel peroxidase and catalase isoforms under oxidative stress-reported here for the first time in marine cyanobacteria. These findings demonstrate that both cyanobacteria possess a dynamic and coordinated ROS defense network, with M. acutissimus showing superior antioxidative stability. The study identifies POD and CAT as reliable biochemical indicators of oxidative stress, establishing Phormidium sp. JMC111 as a potential biomonitor species for environmental oxidative assessment.