Copper (Cu²⁺) is an essential micronutrient for cyanobacteria, but it has a toxic effect above a certain threshold. The presence of Cu²⁺ in water is usually related to human activity due to it being used in pesticides, fertilizer, and algaecides. Previous studies observed that high Cu²⁺ concentrations stimulated toxin synthesis in cyanobacteria and microalgae. Furthermore, saxitoxins (STXs) can bind to Cu²⁺ transporters in microorganisms, decreasing the Cu²⁺ uptake and consequently reducing Cu toxicity. Therefore, considering the invasive capacity of the cyanobacterium Raphidiopsis raciborskii and its potential for STXs production, this study aimed to evaluate the effects of different Cu²⁺ concentrations in the production of STXs and growth of R. raciborskii. In acclimatized growth conditions, cultures of R. raciborskii strain (ITUC01) were exposed to four different copper concentrations for 20 days (0.8, 8, 80, and 800 × 10⁻³ μmol L⁻¹ of CuCl₂). Raphidiopsis raciborskii growth and physiological responses were evaluated measuring the cell concentration, cell volume, biovolume, chlorophyll a levels, and STXs concentration. Comparing the lowest and highest Cu²⁺ concentration (0.8 and 800 × 10⁻³ μmol L⁻¹), it was observed that the increment of Cu²⁺ in the medium led to a reduced maximum growth rate (μ_max), cell concentration, biovolume, and chlorophyll a levels, while the cell volume increased. Despite the low cell concentration and biovolume in the highest Cu²⁺ condition, it was observed that the STXs volumetric concentration was significantly high on day 5, which is indicative of the fact that increased Cu²⁺ concentration might induce STXs production in early growth. In addition, our results revealed that STXs production was uncoupled with growth and a reduction of R. raciborskii toxicity from day 5 to 20 was observed. Therefore, the present study identified some of the survival responses of R. raciborskii in Cu-stressed condition and suggested that Cu²⁺ might be one of the factors that can affect R. raciborskii bloom toxicity.

铜（Cu ²⁺）是蓝细菌必需的微量营养元素，但在一定阈值以上具有毒性作用。水中的Cu ²⁺的存在通常与人类活动有关，因为它被用于农药，肥料和除藻剂中。先前的研究观察到高浓度的Cu ²⁺刺激了蓝藻和微藻中的毒素合成。此外，毒毒素（STXs）可以与微生物中的Cu ²⁺转运蛋白结合，从而降低Cu ^2+的吸收并因此降低Cu的毒性。因此，考虑到蓝藻Raphidiopsis raciborskii的侵袭能力及其产生STX的潜力，本研究旨在评估不同Cu ²⁺浓度对STX产生和R. raciborskii生长的影响。在驯化生长条件下，培养物R. raciborskii菌株（ITUC01）暴露于四种不同的铜的浓度20天（0.8，8，80，和800×10 ^-3 微摩尔大号^-1的CuCl ₂）。通过测量细胞浓度，细胞体积，生物体积，叶绿素a水平和STXs浓度，评估了Raphidiopsis raciborskii的生长和生理反应。比较最低和最高Cu ²⁺浓度（0.8和800×10^-3 微摩尔大号^-1），可以观察到Cu的增量²⁺中导致降低的最大生长速率（该介质μ_最大），细胞浓度，biovolume，和叶绿素一个水平，而细胞体积增加。尽管在最高的Cu ²⁺条件下细胞浓度较低且生物量较低，但观察到STXs的体积浓度在第5天显着较高，这表明Cu ²⁺浓度增加可能会在早期生长中诱导STXs产生。此外，我们的结果表明，STX的产生与生长和R. raciborskii的减少不相关从第5天到第20天观察到毒性。因此，本研究确定了在铜胁迫条件下R.borciborskii的一些存活反应，并暗示Cu ²⁺可能是影响R.borciborskii绽放毒性的因素之一。