The true-branching heterocystous cyanobacterium Fischerella sp. FS 18 is widely distributed in paddy fields (North) and petroleum polluted soils (South) in Iran. This investigation tested the hypothesis that the cyanobacterium can acclimatize under the combined effect of extreme environmental conditions. Here, we analysed the physiological response of the cyanobacterium under extremely limited irradiance (2 μmol photon m⁻² s⁻¹); limited carbon dioxide concentration (no aeration) at alkaline pHs (9 and 11) for up to 96 h. When the cyanobacterium was exposed to these extreme conditions at pH 11, we observed a decline in growth, oxygen liberation, photosystems ratio, chlorophyll a, and phycobilisomes activity compared to pH 9 after 24 h. Besides, we registered a significant decrease in maximum photochemical efficiency and activity of photosystem II at pH 11. The comparative single-cell study revealed that pH 9 caused higher efficiency of photosystem II and I, while increasing alkalinity pH 11 led to disturbed phycobilisomes activity after 24 h. This strain was able to recover its structures after 96 h. In addition, spectroscopy analyses revealed the presence of the Mycosporine-like amino acid at pH 9.

真分支异囊藻蓝藻Fischerella sp。FS 18 广泛分布于伊朗的稻田（北部）和石油污染的土壤（南部）。这项调查检验了蓝藻可以在极端环境条件的综合影响下适应的假设。在这里，我们分析了蓝藻在极其有限的辐照度（2 μmol 光子 m ^-2  s ^-1); 在碱性 pH 值（9 和 11）下，二氧化碳浓度有限（无曝气）长达 96 小时。当蓝藻在 pH 11 的这些极端条件下暴露时，我们观察到 24 小时后与 pH 9 相比，生长、氧释放、光系统比率、叶绿素 a 和藻胆体活性下降。此外，我们发现 pH 11 时光系统 II 的最大光化学效率和活性显着降低。 比较单细胞研究表明，pH 9 导致光系统 II 和 I 的效率更高，而增加碱度 pH 11 导致藻胆体活性受到干扰。 24 小时。该菌株能够在 96 小时后恢复其结构。此外，光谱分析揭示了在 pH 9 时存在类菌孢素氨基酸。