As aquatic ecosystems become increasingly affected by hydrologic alterations, drought and sea level rise a need exists to better understand the biological effects of elevated salinity on toxigenic cyanobacteria such as Microcystis aeruginosa. This study investigated the impacts of oligohaline/low mesohaline conditions and exposure time on selected physiological and biochemical responses in M. aeruginosa including cell viability, oxidative stress, antioxidant responses, in addition to microcystin synthesis and release into the surrounding environment. M. aeruginosa was able to grow in most test salinity treatments (1.4–10 ppt), as supported by cell abundance data and chlorophyll-a (chl-a) concentrations. Physiological data showed that after certain salinity thresholds (∼7ppt) were surpassed, salt stress had cascading effects, such as increased ROS production and lipid peroxidation, potentiating the decline in cellular viability. Furthermore, elevated salinity induced oxidative stress which was concomitant with a decrease in cell abundance, chl-a concentration and photochemical efficiency in the 7–10 ppt treatments. M. aeruginosa did not synthesize microcystins (MCs) in response to increased saline conditions, and mcy-D expression was not correlated with either salinity treatment or extracellular MC concentrations, indicating that salinity stress could inhibit toxin production and that released toxins were likely synthesized prior to exposure. Additionally, extracellular MC concentrations were not correlated with decreased cellular integrity, as evidenced by SYTOX analyses, suggesting that toxins may be released through mechanisms other than cellular lysis. Results from this study support that M. aeruginosa can survive with limited negative impacts to cellular structure and function up to a certain threshold between 7–10 ppt. However, after these thresholds are surpassed, there is radical decline in cell health and viability leading to toxin release. This work underscores the importance of understanding the balance between ROS production and antioxidant capacities when assessing the fate of M. aeruginosa under mesohaline conditions.

随着水生生态系统日益受到水文变化的影响，干旱和海平面上升，有必要更好地了解盐度升高对诸如铜绿微囊藻（Microcystis aeruginosa）等产毒蓝细菌的生物学影响。这项研究调查了低盐度/低中盐度条件和暴露时间对铜绿假单胞菌中选定的生理和生化反应的影响，包括细胞活力，氧化应激，抗氧化反应，以及微囊藻毒素的合成和释放到周围环境中。铜绿假单胞菌在细胞丰度数据和叶绿素a（chl-a）浓度的支持下，大多数测试盐度处理（1.4-10 ppt）都能生长。生理数据表明，超过一定的盐度阈值（约7ppt）后，盐胁迫具有连锁效应，例如ROS产量增加和脂质过氧化，从而增强了细胞活力的下降。此外，盐度升高会诱发氧化应激，这与7-10 ppt处理中细胞丰度，chl-a浓度和光化学效率的降低相伴。铜绿假单胞菌不能合成微囊藻毒素（MCs），以应对盐分增加的情况，而mcy-D的表达与盐度处理或细胞外MC浓度均不相关，表明盐度胁迫可以抑制毒素的产生，并且释放的毒素可能在暴露前合成。此外，如SYTOX分析所证明，细胞外MC浓度与降低的细胞完整性无关，这表明毒素可能通过细胞裂解以外的其他机制释放。这项研究的结果支持铜绿假单胞菌可以存活，对细胞结构的负面影响有限，并且可以在7–10 ppt之间的某个阈值下发挥作用。但是，超过这些阈值后，细胞健康和生存能力会急剧下降，从而导致毒素释放。这项工作强调了在评估中盐条件下铜绿假单胞菌的结局时，了解ROS产生和抗氧化能力之间平衡的重要性。