School of Forestry & Environmental Studies, Yale University, New Haven, 06511, CT, United States; College of Resources and Environmental Science, South-Central University for Nationalities, Wuhan, 430074, China.
School of Forestry & Environmental Studies, Yale University, New Haven, 06511, CT, United States.
Aquat Toxicol. 2019 Oct;215:105271. doi: 10.1016/j.aquatox.2019.105271. Epub 2019 Aug 7.
Microcystis blooms and their associated microcystins pose a significant health risk to humans. Microcystis normally occurs as colonies in eutrophic water bodies, and its physiological tolerance to algaecides is dissimilar to that of unicellular forms. However, the differences of physiological response to algaecides between unicellular and colonial Microcystis have been poorly explored. The current study investigated the effects of hexane extract of Acorus calamus rhizome (HEACR) on the physiological and photosynthetic mechanisms of unicellular and colonial M. aeruginosa in the laboratory. We analyzed the cell density, reactive oxygen species (ROS) level, malonaldehyde (MDA) content, photosynthetic pigments, capsular polysaccharide (CPS), and photosystem (PS II) parameters of the two morphological forms of Microcystis. Our results show that HEACR suppresses the growth of both unicellular and colonial M. aeruginosa, increases the intracellular ROS level and cause lipid peroxidation, as well as exerting a detrimental effect on chlorophyll a (chl a) content and photosynthetic efficiency. Almost 100% inhibition was observed for unicellular and colonial M. aeruginosa after 3 d exposure to 50 and 100 mg L HEACR, respectively. The ROS level increase, MDA accumulation, the chl a decrease and carotenoid increase in unicellular M. aeruginosa were all more obvious than that in colonial cells. The fall in photosynthetic efficiency of unicellular M. aeruginosa were also more significant than that of colonial cells. After 3d exposure, the maximum quantum yield of PS II photochemistry (Fv/Fm), effective quantum yield of PS II photochemistry (Fv'/Fm') and effective quantum yield of photochemical energy conversion in PS II (YII) of unicellular M. aeruginosa was almost totally inhibited by 20 mg L HEACR, while the F/F, F'/F' and YII of colonial M. aeruginosa decreased by 43%, 26% and 66% for 100 mg L of HEACR, respectively. Comparing the two morphological forms of Microcystis, colonies show a greater increase in CPS level to more effectively resist the stress of HEACR and to mitigate ROS generation thereby better defending against oxidative damage. Furthermore, colonial M. aeruginosa shows better photoprotection ability than the unicellular form when exposed to HEACR. The colonies also sustain their maximum electron transport rate, increase their tolerance to strong light, and maintain a higher ability to disperse excess energy. These results demonstrated that HEACR can significantly interfere with the growth and physiological processes of both unicellular and colonial M. aeruginosa, but that colonial M. aeruginosa has a greater ability to adjust physiological tolerance to resist the stresses of HEACR.
微囊藻水华及其相关的微囊藻毒素对人类健康构成重大威胁。微囊藻通常以群体形式存在于富营养水体中，其对杀藻剂的生理耐受性与单细胞形式不同。然而，单细胞和群体微囊藻对杀藻剂的生理响应差异尚未得到充分研究。本研究在实验室条件下，研究了菖蒲根茎正己烷提取物（HEACR）对单细胞和群体铜绿微囊藻生理和光合作用机制的影响。我们分析了两种形态的微囊藻的细胞密度、活性氧（ROS）水平、丙二醛（MDA）含量、光合色素、荚膜多糖（CPS）和光系统（PS II）参数。结果表明，HEACR 抑制了单细胞和群体铜绿微囊藻的生长，增加了细胞内 ROS 水平并导致脂质过氧化，对叶绿素 a（chl a）含量和光合作用效率产生有害影响。暴露于 50 和 100 mg/L HEACR 3 天后，单细胞和群体铜绿微囊藻的抑制率分别达到近 100%。单细胞微囊藻的 ROS 水平升高、MDA 积累、chl a 下降和类胡萝卜素增加均比群体细胞更为明显。单细胞铜绿微囊藻的光合效率下降也比群体细胞更为显著。暴露 3d 后，20 mg/L HEACR 几乎完全抑制了单细胞铜绿微囊藻 PS II 光化学的最大量子产量（Fv/Fm）、PS II 光化学的有效量子产量（Fv'/Fm'）和 PS II 光化学能量转换的有效量子产量（YII），而 100 mg/L HEACR 对群体铜绿微囊藻的 F/F、F'/F'和 YII 分别降低了 43%、26%和 66%。与两种形态的微囊藻相比，群体显示出更高的 CPS 水平增加，以更有效地抵抗 HEACR 的胁迫并减轻 ROS 的产生，从而更好地抵御氧化损伤。此外，暴露于 HEACR 时，群体铜绿微囊藻比单细胞形式具有更好的光保护能力。群体还维持其最大电子传递速率，增加对强光的耐受性，并保持更高的分散多余能量的能力。这些结果表明，HEACR 可显著干扰单细胞和群体铜绿微囊藻的生长和生理过程，但群体铜绿微囊藻具有更大的生理耐受调节能力，以抵抗 HEACR 的胁迫。
