Elucidating the role of compatible solutes in growth protection and amelioration of oxidative stress in the thermophilic cyanobacterium Mastigocladus sp. TA-8 during temperature shifts.

This study explores the protective roles of three compatible solutes i.e. sucrose, trehalose, and proline, against temperature-induced cellular damages in the thermophilic cyanobacterium Mastigocladus sp. TA-8. The organism was exposed to sub-optimal (25 °C) and supra-optimal (50 °C) temperatures from its optimal 45 °C, with and without solute supplementation. Morphological, physiological, biochemical, and transcript-level alterations were analyzed. The maximum growth inhibition was occurred at 25 °C, accompanied by elevated reactive oxygen species, malondialdehyde content and redox imbalance. Nitrogen metabolism was also significantly impaired at 25 °C and evidenced by reduced total nitrogen, decreased glutamine synthetase activity, and altered α-ketoglutarate levels. At 50 °C, photosynthetic efficiency was predominantly reduced where sucrose was more effective in providing protection, likely due to enhanced ROS scavenging and increased antioxidant enzyme activities, improved redox potential and reduced MDA levels. Contrastingly, proline and trehalose conferred huge protection at 25 °C. Additionally, proline also fulfilled the nitrogen requirement at lower temperature, evidenced by higher glutamate and total nitrogen level, along with the upregulation of proline catabolism gene p5cdh. Conclusively, findings suggested that the compatible solutes played a major contribution in the protection against oxidative damage induced by thermal stress and maintaining cellular redox balance in Mastigocladus sp. TA-8.